A Concise History of the World (Part 1)
Created | Updated Aug 31, 2008
The goal of this entry is to provide a complete summary of the events of the history of the world, as we know it in the beginning of the 21st century.
The first part deal with “Natural History”, the second with “Political History” Natural history is defined as the scientific research about plants or animals and other objects, as the planets and stars, leaning more towards the observational than experimental methods of study, and encompasses more research that is published in magazines than in academic journals. The name derives from Naturalis Historia (Latin for "Natural History") is an encyclopedia written circa AD 77 by Pliny the Elder. DISCLAIMER: the entry is a COMPILATION of what I think is notably between the things I red so a lot of this you can find around I do not quote the sources only because they would be longer tan the text himself! This phrase is intended as acknowledgments to the entire world of science. For simplicity I use plain text instead of a formatted text.
The term "universe" may be used in slightly different contextual senses, denoting such concepts as the cosmos, the world or Nature. Lucretius the first known author that used the word did it in the sense "everything rolled into one, everything combined into one".
Universe (or the World) is here defined and used as "everything that physically exists": the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them. However, the Astronomical observations indicate that the universe is 11 to 20 billion (the best bet is 13.73 ± 0.12 billion) years old and at least 93 billion light years across, while 3×10^52 kg is the Mass of the observable universe. It may seem paradoxical that two point can be separated by a distance that is more tan seven times the years of the universe; however, this - we are granted - is a simple consequence of general relativity.
There are three elements constituting the universe (space-time, matter-energy, and physical law) that correspond roughly to the ideas of Aristotle. In his book The Physics (Greek word for Nature from which we derive the word "physics"), Aristotle divided everything into three roughly analogous elements: matter (the stuff of which the universe is made), form (the arrangement of that matter in space) and change (how matter is created, destroyed or altered in its properties, and similarly, how form is altered). Other idea that discern natura naturans (the active principles governing the universe) from natura naturata, the passive elements upon which the former act, as in Averroes and Spinoza do not interest us.
The universe is believed to be mostly composed of dark energy and dark matter, both of which are poorly understood at present. Only about 4% of mass of the universe is ordinary matter. A relatively small perturbation, so to speak.
The early universe is supposed to be knowable (also theoretically) only from a certain point of tome forward, called the Plank Time, the preceding period being called "The Age of St. Augustine".
The phrase "Augustinian Era" proposed in 1952, by George Gamow, is meant to convey the idea that the known laws of physics break down in a gravitational singularity of infinite density at the time zero of the Big Bang, so that according to Albert Einstein's general theory of relativity there were no times prior to that point. However, physicists believe that general relativity becomes incompatible with quantum mechanics at the Planck scale, so that the predictions of general relativity cannot be trusted before the Planck era when energies and temperatures reached the Planck scale, and that we need a theory of quantum gravitation before we can say anything about times before the Planck era.
The Planck epoch followed The Age of St. Augustine, up to 10^-43 seconds after the Big Bang: during this time, if supersymmetry theory is correct, the four fundamental forces - electromagnetism, weak nuclear force, strong nuclear force and gravitation - all had the same strength, so they are possibly unified into one fundamental force. Little is known about this epoch, and different theories propose different scenarios. The size of universe is less than the size of an atom, at this point.
Then follows the Grand Unification Epoch, lasting between 10^-43 seconds and 10^-36 seconds after the Big Bang, when as the universe expands and cools from the Planck epoch, gravitation begins to separate from the fundamental gauge interactions: electromagnetism and the strong and weak nuclear forces. Physics at this scale may be described by a grand unified theory in which the gauge group of the Standard Model is embedded in a much larger group, which is broken to produce the observed forces of nature. Eventually, the grand unification is broken as the strong nuclear force separates from the electroweak force. This occurs as soon as inflation does. According to some theories, this should produce magnetic monopoles. Unification of the strong and electroweak forces means that the only particle expected at this time is the Higgs boson.
Between 10^-36 seconds and 10^-12 seconds after the Big Bang is the Electroweak Epoch. Now the temperature of the universe is low enough (10^28K) to separate the strong force from the electroweak force (the name for the unified forces of electromagnetism and the weak interaction). This phase transition triggers a period of exponential expansion known as cosmic inflation. After inflation ends, particle interactions are still energetic enough to create large numbers of exotic particles, including W and Z bosons and Higgs bosons.
Between 10^-36 seconds and 10^-32 seconds after the Big Bang the temperature, and therefore the time, at which cosmic inflation occurs is not known for certain. And this period is termed The Inflationary Epoch: during inflation, the universe is flattened (its spatial curvature is critical) and the universe enters a homogeneous and isotropic rapidly expanding phase in which the seeds of structure formation are laid down in the form of a primordial spectrum of nearly-scale-invariant fluctuations. Some energy from photons becomes virtual quarks and hyperons, but these particles decay quickly. One scenario suggests that prior to cosmic inflation, the universe was cold and empty, and the immense heat and energy associated with the early stages of the big bang was created through the phase change associated with the end of inflation.
A Reheating phase seems to be associate at the inflationary period. During reheating, the exponential expansion that occurred during inflation ceases and the potential energy of the inflation field decays into a hot, relativistic plasma of particles. If grand unification is a feature of our universe, then cosmic inflation must occur during or after the grand unification symmetry is broken, otherwise magnetic monopoles would be seen in the visible universe. At this point, the universe is dominated by radiation; quarks, electrons and neutrinos form. Someone think the size of the universe as big as a toy ball, now.
No known physics can explain the fact that there are in the universe so many more particles called baryons than antibaryons.
Supersymmetry breaking (if supersymmetry is a property of our universe) was followed by The Quark epoch (between 10^-12 seconds and 10-6 seconds) and by (between 10^-6 seconds and 1 second after the Big Bang the Hadron epoch and Lepton epoch between 1 second and 3 minutes after the Big Bang.
The majority of hadrons and anti-hadrons annihilate each other at the end of the hadron epoch, leaving leptons and anti-leptons dominating the mass of the universe. Approximately 3 seconds after the Big Bang the temperature of the universe falls to the point where new lepton/anti-lepton pairs are no longer created and most leptons and anti-leptons are eliminated in annihilation reactions, leaving a small residue of leptons.
More or less at this point the whole globe himself was almost behaving as an avalanche rolling down the slope of a mountain, at least as the laws of physics are concerned. And now the whole that exist is approximately the size of our Solar System!
After most leptons and anti-leptons are annihilated at the end of the lepton epoch the energy of the universe is dominated by photons. These photons are still interacting frequently with charged protons, electrons and (eventually) nuclei, and continue to do so for the next 300,000 years. Now between 3 minutes and 380,000 years after the Big Bang the Universe is living the Photon epoch
The next quarter of an hour meaning from 3 minutes to 20 minutes after the Big Bang the Nucleosynthesis occours. Now the temperature of the universe had fallen to the point where atomic nuclei can begin to form. Protons (hydrogen ions) and neutrons begin to combine into atomic nuclei in the process of nuclear fusion. However, nucleosynthesis only lasts for about seventeen minutes, after which time the temperature and density of the universe has fallen to the point where nuclear fusion cannot continue. At this time, there is about three times more hydrogen than helium-4 (by mass) and only trace quantities of other nuclei.
At this time, the densities of non-relativistic matter (atomic nuclei) and relativistic radiation (photons) are equal. The Jeans length, which determines the smallest structures that can form (due to competition between gravitational attraction and pressure effects), begins to fall and perturbations, instead of being wiped out by radiation free-streaming, can begin to grow in amplitude.
Obviously one can be very surprised of the speeding of the phenomenon, but could be that in this form of universe our time does not make sense
The Age of Recombination. Hydrogen and helium atoms begin to form and the density of the universe falls. This is thought to have occurred somewhere between 240,000 and 310,000 years after the Big Bang. Hydrogen and helium are at the beginning ionized, i.e. no electrons are bounded to the nuclei, which are therefore electrically charged (+1 and +2 respectively). As the universe cools down, the electrons get captured by the ions making them neutral. This process is relatively fast (actually faster for the helium than for the hydrogen) and is known as recombination. At the end of recombination, most of the atoms in the universe are neutral, therefore the photons can now travel freely: the universe has become transparent. The photons emitted right after the recombination, that can therefore travel undisturbed, are those that we see in the cosmic microwave background (CMB) radiation. Therefore the CMB is a picture of the universe at the end of this epoch.
Structure formation in the big bang model proceeds hierarchically, with smaller structures forming before larger ones. The first structures to form are quasars, which are thought to be bright, early active galaxies, and population III stars.
The first stars, most likely Population III stars, form and start the process of turning the light elements that were formed in the Big Bang (hydrogen, helium and lithium) into heavier elements. However, as of yet there have been no observed Population III stars, which leaves their formation a mystery.
Large volumes of matter collapse to form a galaxy. Population II stars are formed early on in this process, with Population I stars formed later.
Based upon the emerging branch of astronomy, nucleocosmochronology, the Galactic thin disk of the Milky Way is estimated to have been formed 8.3 ± 1.8 billion years ago.
Gravitational attraction pulls galaxies towards each other to form groups, clusters and superclusters. The Virgo Supercluster (or Local Supercluster) is the galactic supercluster that contains the Local Group, the latter containing, in its turn, the Milky Way and Andromeda galaxies. As the best current data estimate the age of the universe today as 13.7 billion years since the big bang the matter in our supercluster was a sample of the 5 billion years old universe. Since the expansion of the universe appears to be accelerating (due more than other to dark energy), superclusters are likely to be the largest structures that will ever form in the universe. As he present accelerated expansion prevents any more inflationary structures entering the horizon and prevents new gravitationally bound structures from forming.
Finally, objects on the scale of our solar system form. Our sun (The Sun) formed roughly 5 billion years ago, or roughly 8 to 9 billion years after the big bang, about 3 billions after the local cluster is a late-generation star, incorporating the debris from many generations of earlier stars.
The Solar System in broad terms, consist of the Sun, four inner planets, in order of their distances from the Sun, the "terrestrial" planets are: Mercury, Venus, the Earth and Mars. An asteroid belt composed of small rocky bodies, Ceres the largest object in the asteroid belt separate this four from the four gas giant outer planets (or Jovians): Jupiter, Saturn, Uranus and Neptune and a second belt, the Kuiper belt, composed of icy objects. Pluto, Makemake are the largest Kuiper belt objects. Eris is the largest known object in the scattered disc, beyond the Kuiper belt. Outward are: the scattered disc, the heliopause, and ultimately the hypothetical Oort cloud.
Six of the eight planets and two of the dwarf planets are in turn orbited by natural satellites, usually termed "moons" after Earth's Moon, and each of the outer planets is encircled by planetary rings of dust and other particles, Saturn’s rings the most famous. All the "true" planets except Earth, and a lot of the other objects, are named after deities from Greco-Roman mythology.
The principal component of the Solar System is the Sun, a main sequence G2 star that contains 99.86 percent of the system's known mass and dominates it gravitationally. Jupiter and Saturn, the Sun's two largest orbiting bodies, account for more than 90 percent of the system's remaining mass.
Jupiter is just about as large in diameter as a gas planet can be. If more material were to be added, it would be compressed by gravity such that the overall radius would increase only slightly. A star can be larger only because of its internal (nuclear) heat source, but Jupiter would have to be at least 80 times more massive to become a star. Also if not a star Jupiter radiates more energy into space than it receives from the Sun, in this respect is the only other source of energy in the system: the interior of Jupiter is hot: the core is probably about 20,000 K, the heat being generated by the Kelvin-Helmholtz mechanism, the slow gravitational compression of the planet. (Jupiter does NOT produce energy by nuclear fusion as in the Sun; it is much too small and hence its interior is too cool to ignite nuclear reactions.)
The form of the system is ruled and determined by the energy of the Sun and the gravity law (the attractive force of Jupiter seems to be responsible for the asteroid belt not forming a planet.
The most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic while comets and Kuiper belt objects are usually at significantly greater angles to it.
The Solar System is believed to have formed according to the nebular hypothesis, which holds that it emerged from the gravitational collapse of a giant molecular cloud 4-6 billions years ago. This initial cloud was likely several light-years across and probably birthed several stars. Studies of ancient meteorites reveal traces of elements only formed in the hearts of very large exploding stars, indicating that, with the most probability, the Sun formed within a star cluster, and in range of a number of nearby supernovae explosions. The shock wave from these supernovae may have triggered the formation of the Sun by creating regions of overdensity in the surrounding nebula, allowing gravitational forces to overcome internal gas pressures and cause the collapse.
The region that would become the Solar System, known as the pre-solar nebula, had a diameter of between 7000 and 20,000 Astronomical Units (AU, an AU equals the mean distance between the Earth and the Sun - approximately 150 million km or 93 million miles) and a mass just over that of the Sun. As the nebula collapsed, conservation of angular momentum made it rotate faster. As the material within the nebula condensed, the atoms within it began to collide with increasing frequency. The centre, where most of the mass collected, became increasingly hotter than the surrounding disc. As gravity, gas pressure, magnetic fields, and rotation acted on the contracting nebula, it began to flatten into a spinning protoplanetary disc with a diameter of roughly 200 AU and a hot, dense protostar at the centre.
Studies of T Tauri stars, young, pre-fusing solar mass stars believed to be similar to the Sun at this point in its evolution, show that discs of pre-planetary matter often accompany them. These discs extend to several hundred AU and reach only a thousand Kelvin at their hottest.
Within 50 million years, the pressure and density of hydrogen in the centre of the collapsing nebula became great enough for the proto-sun to begin thermonuclear fusion. The temperature, reaction rate, pressure, and density increased until hydrostatic equilibrium was achieved, with the thermal energy countering the force of gravitational contraction. At this point the Sun became a full-fledged main sequence star.
From the remaining cloud of gas and dust (the "solar nebula"), the various planets formed. They are believed to have formed by accretion: the planets began as dust grains in orbit around the central protostar; then gathered by direct contact into clumps between one and ten meters in diameter; then collided to form larger bodies (planetesimals) of roughly 5 km in size; then gradually increased by further collisions at roughly 15 cm per year over the course of the next few million years.
The inner Solar System was too warm for volatile molecules like water and methane to condense, and so the planetesimals which formed there were relatively small (comprising only 0.6% the mass of the disc) and composed largely of compounds with high melting points, such as silicates and metals. These rocky bodies eventually became the terrestrial planets. Farther out, the gravitational effects of Jupiter made it impossible for the protoplanetary objects present to come together, leaving behind the asteroid belt.
Farther out still, beyond the frost line, where more volatile icy compounds could remain solid, Jupiter and Saturn became the gas giants. Uranus and Neptune captured much less material and are known as ice giants because their cores are believed to be made mostly of ices (hydrogen compounds).
Once the young Sun began producing energy, the solar wind blew the gas and dust in the protoplanetary disk into interstellar space and ended the growth of the planets. T Tauri stars have far stronger stellar winds than more stable, older stars.
Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the Earth, Planet Earth, the World, and Terra, home to millions of species, including humans; Earth is the only place in the universe where life is known to exist.
Scientific evidence indicates that the planet formed 4.54 billion years ago, and life appeared on its surface within a billion years. Since then, Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful radiation, permitting life on land.
Earth's outer surface is divided into several rigid segments, or tectonic plates, that gradually migrate across the surface over periods of many millions of years. About 71% of the surface is covered with salt-water oceans, the remainder consisting of continents and islands; liquid water, necessary for all known life, is not known to exist on any other planet's surface. Earth's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core.
Earth interacts with other objects in outer space, including the Sun and the Moon. At present, Earth orbits the Sun once for every roughly 366.26 times it rotates about its axis. This length of time is a sidereal year, which is equal to 365.26 solar days. The Earth's axis of rotation is tilted 23.4° away from the perpendicular to its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). Earth's only known natural satellite, the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides, stabilizes the axial tilt and gradually slows the planet's rotation. A cometary’s bombardment during the early history of the planet played a role in the formation of the oceans. Later, asteroid impacts caused significant changes to the surface environment. Earth and the other planets in the Solar System formed 4.54 billion years ago, as previously told, the Moon formed soon afterwards, possibly as the result of a Mars-sized object (sometimes called Theia) with about 10% of the Earth's mass impacting the Earth in a glancing blow: some of this object's mass would have merged with the Earth and a portion would have been ejected into space, but enough material would have been sent into orbit to form the Moon.
Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice and liquid water delivered by asteroids and the larger proto-planets, comets, and trans-Neptunian objects produced the oceans. The highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago, and half a billion years later, the last common ancestor of all life existed. The details of the origin of life are unknown, though the broad principles have been established. Two schools of thought regarding the origin of life have been proposed. The first suggests that organic components may have arrived on Earth from space (see "Panspermia"), while the other argues for terrestrial origins. In the long run the mechanisms by which life would initially arise are nevertheless held to be similar, so the first hypothesis is just a complication more. If life arose on Earth, the timing of this event is highly speculative-perhaps it arose around 4 billion years ago. In the energetic chemistry of early Earth, a molecule (or even something else) gained the ability to make copies of itself-the replicator. The nature of this molecule is unknown, its function having long since been superseded by life's current replicator, DNA. In making copies of itself, the replicator did not always perform accurately: some copies contained an "error." If the change destroyed the copying ability of the molecule, there could be no more copies, and the line would "die out." On the other hand, a few rare changes might make the molecule replicate faster or better: those "strains" would become more numerous and "successful" hence evolution arose. As choice raw materials ("food") became depleted, strains, which could exploit different materials, or perhaps halt the progress of other strains and steal their resources, became more numerous.
Several different models have been proposed explaining how a replicator might have developed. Different replicators have been posited, including organic chemicals such as modern proteins, nucleic acids, phospholipids, and crystals. There is currently no method of determining which of these models, if any, closely fits the origin of life on Earth. One of the older theories, and one which has been worked out in some detail, will serve as an example of how this might occur. The high energy from volcanoes, lightning, and ultraviolet radiation could help drive chemical reactions producing more complex molecules from simple compounds such as methane and ammonia, among these were many of the relatively simple organic compounds that are the building blocks of life. As the amount of this "organic soup" increased, different molecules reacted with one another. Sometimes more complex molecules would result (perhaps clay provided a framework to collect and concentrate organic material). All this continued for a very long time, with reactions occurring more or less at random, until by chance there arose a new molecule: the replicate. This had the bizarre property of promoting the chemical reactions that produced a copy of itself, and evolution began properly. Biologists have tentatively traced the most recent common ancestor of all life to an aquatic microorganism that lived in extremely high temperatures many biologists hypothesize that this step led to an "RNA world" in which RNA did many jobs, storing genetic information, copying itself, and performing basic metabolic functions. Eventually DNA took over the function of the replicator at some point so that now (with the exception of some viruses and prions) all known life use DNA as replicator, in an almost identical manner.
It was bacteria that gave life its initial foothold, and it was bacteria by the trillions that engineered the planet for our use, taking in carbon dioxide and giving off oxygen, day in and day out for billions of years until there was enough oxygen in the atmosphere to support larger life.
The oldest known fossilized prokaryotes were laid down approximately 3.5 billion years ago, only about 1 billion years after the formation of the earth's crust. Even today, prokaryotes are perhaps the most successful and abundant life forms. Eukaryotes only formed later, from endosymbiosis of multiple prokaryote ancestors. The prokaryotes are divided into two domains: the bacteria and the archaea. Archaea are a newly appointed domain of life. These organisms were originally thought to live only in inhospitable conditions such as extremes of temperature, pH, and radiation but have since been found in all types of habitats. The oldest known fossil eukaryotes are about 1.7 billion years old. However, some genetic evidence suggests eukaryotes appeared as early as 3 billion years ago.
The biochemical capacity to use water as the source for electrons in photosynthesis evolved once, in a common ancestor of extant cyanobacteria. The geological record indicates that this transforming event took place early in Earth's history, at least 2450-2320 million years ago, and possibly much earlier. The development of photosynthesis allowed the Sun's energy to be harvested directly by life forms; the resultant oxygen accumulated in the atmosphere and resulted in a layer of ozone (a form of molecular oxygen [O3]) in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes. True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, life colonized the surface of Earth.
Beginning with almost no dry land, the total amount of surface lying above the oceans has steadily increased. During the past two billion years, for example, the total size of the continents has doubled. As the surface continually reshaped itself, over hundreds of millions of years, continents formed and broke up. The continental plaques migrate across the surface of the globe, occasionally combining to form a super continent. Roughly 750 million years ago, the earliest known supercontinent, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600-540 millions years ago, then finally Pangaea, which broke apart 180 millions years ago.
Since the 1960s, it has been hypothesized that severe glacial action between 750 and 580 millions years ago, during the Neoproterozoic, covered much of the planet in a sheet of ice. This hypothesis has been termed "Snowball Earth", and is of particular interest because it preceded the Cambrian explosion, when multicellular life forms began to proliferate.
For most of the nearly 4 billion years that life has existed on Earth, evolution produced little beyond bacteria, plankton, and multi-celled algae. But beginning about 600 million years ago in the Precambrian, the fossil record speaks of more rapid change. First, there was the rise and fall of mysterious creatures of the Ediacaran fauna, named for the fossil site in Australia where they were first discovered. Some of these animals may have belonged to groups that survive today, but others don't seem at all related to animals we know. Then, between about 570 and 530 million years ago, another burst of diversification occurred, with the eventual appearance of the lineages of almost all animals living today. This stunning and unique evolutionary flowering is termed the "Cambrian explosion," taking the name of the geological age in whose early part it occurred. But it was not as rapid as an explosion: the change seems to have happened in a range of about 30 million years, and some stages took 5 to 10 million years.
It's important to remember that what we call "the fossil record" is only the available fossil record. In order to be available to us, the remains of ancient plants and animals have to be preserved first, and this means that they need to have fossilizable parts and to be buried in an environment that will not destroy them. It has long been suspected that the sparseness of the pre-Cambrian fossil record reflects these two problems. First, organisms may not have sequestered and secreted much in the way of fossilizable hard parts; and second, the environments in which they lived may have characteristically dissolved those hard parts after death and recycled them. An exception was the mysterious "small shelly fauna" -- minute shelled animals that are hard to categorize -- that left abundant fossils in the early Cambrian. Recently, minute fossil embryos dating to 570 million years ago have also been discovered. Even organisms that hadn't evolved hard parts, and thus didn't leave fossils of their bodies, left fossils of the trails they made as they moved through the Precambrian mud. Life was flourishing long before the Cambrian "explosion".
The best record of the Cambrian diversification is the Burgess Shale in British Columbia. Laid down in the middle-Cambrian, when the "explosion" had already been underway for several million years, this formation contains the first appearance in the fossil record of brachiopods, with clamlike shells, as well as trilobites, mollusks, echinoderms, and many odd animals that probably belong to extinct lineages. They include Opabinia, with five eyes and a nose like a fire hose, and Wiwaxia, an armored slug with two rows of upright scales. The question of how so many immense changes occurred in such a short time is one that stirs scientists. Why did many fundamentally different body plans evolve so early and in such profusion? Some point to the increase in oxygen that began around 700 million years ago, providing fuel for movement and the evolution of more complex body structures. Others propose that an extinction of life just before the Cambrian opened up ecological roles, or "adaptive space," that the new forms exploited. External, ecological factors like these were undoubtedly important in creating the opportunity for the Cambrian explosion to occur, but internal, genetic factors were also crucial. Recent research suggests that the period prior to the Cambrian explosion saw the gradual evolution of a "genetic tool kit" of genes that govern developmental processes. Once assembled, this genetic tool kit enabled an unprecedented period of evolutionary experimentation, and competition. Many forms seen in the fossil record of the Cambrian disappeared without trace. Once the body plans that proved most successful came to dominate the biosphere, evolution never had such a free hand again, and evolutionary change was limited to relatively minor tinkering with the body plans that already existed.
Interpretations of this critical period are subject of lively debate among scientists like Stephen Jay Gould of Harvard University and Simon Conway Morris of Cambridge University. Gould emphasizes the role of chance. He argues that if one could "rerun the tape" of that evolutionary event, a completely different path might have developed and would likely not have included a humanlike creature. Morris, on the other hand, contends that the environment of our planet would have created selection pressures that would likely have produced similar forms of life to those around us, including humans.
At this point the classifications of times became impressive and complicated
There are Eras, Periods, Subperiods and Epochs now will follows a series of epoch and periods an their main fact.
505 millions years ago is the Ordovician period. Invertebrates are dominant, but the first fishes appear.
Mesozoic (from 251.0 to 65.5 million years ago, meaning from Greek and means "middle life", as it is an era of geologic time between the Paleozoic and the Cenozoic.
251.0 to 199.6 million years ago Triassic sees the emerging of dinosaurs and also egg-laying mammals. From about 280-230 million years ago, (Late Paleozoic Era until the Late Triassic) the continent we now know as North America was continuous with Africa, South America, and Europe, archosaurs (forbearers of crocodiles dinosaurs and birds first appeared in the late Permian more or less at this point. Pangea first began to be torn apart when a three-pronged fissure grew between Africa, South America, and North America. There were three major phases in the break-up of Pangaea. The first phase began in the Early-Middle Jurassic, when Pangaea created a rift from the Tethys Ocean in the east and the Pacific in the west. The rifting took place between North America and Africa, and produced multiple failed rifts. The rift resulted in a new ocean, the Atlantic Ocean. This first division was important because about at this time in the southern continent 213 millions years ago developed the Marsupial mammals. This is the Jurassic 199.6 to 145.5 million years ago, in which the dinosaurs outpaced mammal in evolution becoming the most visible form of life on Earth
In the Mesozoic (145.5 to 65.5 million years ago) Cretaceous Dinosaurs reach their peak, while primitive placental mammals appeared. This group appears to be original of the north hemisphere, where they outpaced the marsupials. Mammals and near-mammals expanded out of the nocturnal insectivore niche from the mid Juraassic onwards. The traditional view is that: mammals only took over the medium- to large-sized ecological niches in the Cenozoic, after the extinction of the dinosaurs; but then they diversified very quickly, for example the earliest known bat dates from about 50 million years ago, only 15 million years after the extinction of the dinosaurs.
Following the Cambrian explosion, about 535 millions years ago, there have been five mass extinctions. The last extinction event occurred 65 millions years ago, when a meteorite collision probably triggered the extinction of the (non-avian) dinosaurs and other large reptiles, but spared small animals such as mammals, that profited of the disappearance of the big reptiles.
Over the past 65 million years, mammalian life has diversified, conquering every corner of the planet an in many cases topping the food ladder.
Several millions years ago, an African ape-like animal gained the ability to stand upright. This enabled tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain and a very different rate of reproduction from the other apelike species. The development of agriculture, and then civilization, allowed humans to influence the Earth in a short time span as no other life form had, affecting both the nature and quantity of other life forms. And will be summarized below.
The present pattern of ice ages began about 40 millions years ago, then intensified during the Pleistocene about 3 millions years ago. The Polar Regions have since undergone repeated cycles of glaciation and thaw, repeating every 40-100,000 years. The last ice age ended 10,000 years ago. 2000 years later civilization began.
We are now at just a little over the half of the proposed length of this writing. History of life on Earth account more or less for one fourth of the time but the history of men just 0.0036496%. Of course it's only our pride that account for its, importance.
We must not forget that although what we usually see are the big animals, T-Rex, elephants and whales, lions, cows and man the big Phylun is the one called Arthropoda the major group arthropods are the Insects (Class Insecta) that are a major group of and the most diverse group of animals on the Earth, with over a million described species-more than half of all known living organisms with estimates of undescribed species as high as 30 million, thus potentially representing over 90% of the differing life forms on the planet. Insects may be found in nearly all environments on the planet, although only a small number of species occur in the oceans, a habitat dominated by another arthropod group, the crustaceans.
There are approximately 5,000 dragonfly species, 2,000 praying mantises, 20,000 grasshoppers, 170,000 butterflies and moth, 120,000 fly, 82,000 true bug, 360,000 beetle, and 110,000 bees, wasp and ant species described to date. Estimates of the total number of current species, including those not yet known to science, range from two million to fifty million, with newer studies favouring a lower figure of about six to ten million. Adult modern insects range in size from a 0.139 mm (0.00547 in) firefly (Dicopomorpha echmepterygis) to a 55.5 cm (21.9 in) long stick insect (Phobaeticus serratipes). The heaviest documented insect was a Giant Weta of 70 g (21/2 oz), but other possible candidates include the Goliath beetles Goliathus goliatus, Goliathus regius and Cerambycid beetles such as Titanus giganteus, though no one is certain which is truly the heaviest.
And also in the mammalian group we tend to underestimate the little one, as mice, until they became the essential cause of the black death of a famine. Dealing with the adoption of agriculture we will return to this topic.
Now we simply introduce the R-K concept.
Reproductive strategies can be classified into two major types: r and k strategies. Species, which practice r-strategies usually, emphasize gamete production, mating behavior, low parental care, and high reproductive rates. Species, which practice k-strategies, conversely emphasize high parental care; lower reproductive rates, resource acquisition and a higher degree of social complexity. The k-strategy requires a more complex nervous system as well as larger brains than the primarily r-strategist species do.
In nature, we can see the difference between extreme cases of r and k strategist species. For example, an oyster can produce 500 million eggs a year, while the great apes can reproduce only one infant every 5 or 6 years. Thus, the oyster will have reproduced itself 2500 million times, by the time a great ape will have reproduced itself once. The oyster will not spend any time "parenting" over its offspring, while the great ape will put much time and energy into nurturing their offspring. And also little mammalian are on the r side.
While primates in general are the most k-strategist of all of the species, there still remain differences between them. For example, a lemur is more r-strategist than a gorilla. In fact, going across the primate spectrum, research has shown that primates become more k-strategist with increasing size, and so they born less babies. An exception seems to be the human ape, that as a faster reproductive rate, the fact will be discussed below.
As for today there are SEVEN extant apes: Gibbon, Siamang, Orangutan, Gorilla, Chimpanzee, Bonobo, ...and... Human (aka Homo sapiens sapiens).
But it was not always so. Apes are the members of the Hominoidea superfamily of primates, which includes humans. Under the current classification system there are two families of hominoids: the family Hylobatidae consists of 4 genera and 13 species of gibbons, including the Lar Gibbon and the Siamang, collectively known as the lesser apes. The family Hominidae consisting of orangutans, gorillas, chimpanzees, and humans, collectively known as the great apes.
A few other primates, such as the Barbary Ape, have the word "ape" in their common names (usually to indicate lack of a tail), but they are not regarded as true apes. All the Apes belong to the Primates order. The Primates order is divided informally into three main groupings: prosimians, monkeys of the New World, and monkeys and apes of the Old World. Primates appeared about 63 million years ago, as soon there were no more dinosaurs around, it seems. The time of the split between humans and living apes used to be thought to have occurred 15 to 20 million years ago, or even up to 30 or 40 million years ago. Some apes occurring within that time period, such as Ramapithecus, used to be considered as hominids, and possible ancestors of humans. Later fossil finds indicated that Ramapithecus was more closely related to the orang-utan, and new biochemical evidence indicated that the last common ancestor of hominids and apes occurred between 5 and 10 million years ago, and probably in the lower end of that range. Ramapithecus therefore is no longer considered a hominid.
Hominid Species
The species here are listed roughly in order of appearance in the fossil record (note that this ordering is not meant to represent an evolutionary sequence), except that the robust australopithecines are kept together. Each name consists of a genus name (e.g. Australopithecus, Homo), which is always capitalized, and a specific name (e.g. africanus, erectus), which is always in lower case. Within the text, genus names are often omitted for brevity. Each species has a type specimen that was used to define it.
Sahelanthropus tchadensis, fossils discovered in Chad in Central Africa. It is the oldest known hominid or near-hominid species, dated at between 6 and 7 million years old. The skull has a very small brain size of approximately 350 cc. It is not known whether it was bipedal. So it is close to the common ancestor of humans and chimpanzees.
Orrorin tugenensis. In western Kenya. The fossils include fragmentary arm and thighbones, lower jaws, and teeth and were discovered in deposits that are about 6 million years old. Its finders have claimed that Orrorin was a human ancestor adapted to both bipedality and tree climbing, and that the australopithecines are an extinct offshoot.
Ardipithecus ramidus: it was originally dated at 4.4 million years, but has since been discovered to far back as 5.8 million years. Most remains are skull fragments. Indirect evidence suggests that it was possibly bipedal, and that some individuals were about 122 cm (4'0") tall.
Australopithecus anamensis
From Kanapoi in Kenya, and 12 fossils, mostly teeth found in 1988, from Allia Bay in Kenya (Leakey et al. 1995). Anamensis existed between 4.2 and 3.9 million years ago, and has a mixture of primitive features in the skull, and advanced features in the body. There is strong evidence of bipedality, and a lower humerus (the upper arm bone) is extremely humanlike.
Australopithecus afarensis
A. afarensis existed between 3.9 and 3.0 million years ago. Afarensis had an apelike face with a low forehead, a bony ridge over the eyes, a flat nose, and no chin. They had protruding jaws with large back teeth. Cranial capacity varied from about 375 to 550 cc. The skull is similar to that of a chimpanzee, except for the more humanlike teeth. The canine teeth are much smaller than those of modern apes, but larger and more pointed than those of humans, and shape of the jaw is between the rectangular shape of apes and the parabolic shape of humans. However and that is the interesting feature) their pelvis and leg bones far more closely resemble those of modern man, and leave no doubt that they were bipedal (although adapted to walking rather than running). Their bones show that they were physically very strong. Females were substantially smaller than males, a condition known as sexual dimorphism. Height varied between about 107 cm (3'6") and 152 cm (5'0"). The finger and toe bones are curved and proportionally longer than in humans, but the hands are similar to humans in most other details. Most scientists consider this evidence that afarensis was still partially adapted to climbing in trees, others consider it evolutionary baggage.
Kenyanthropus platyops
Found in Kenya with an unusual mixture of features (Leakey et al. 2001). It is aged about 3.5 million years old. The size of the skull is similar to A. afarensis and A. africanus, and has a large, flat face and small teeth.
Australopithecus africanus
A. africanus existed between 3 and 2 million years ago. It is similar to afarensis, and was also bipedal, but body size was slightly greater. Brain size may also have been slightly larger, ranging between 420 and 500 cc. This is a little larger than chimp brains (despite a similar body size), but still not advanced in the areas necessary for speech. The back teeth were a little bigger than in afarensis. Although the teeth and jaws of africanus are much larger than those of humans, they are far more similar to human teeth than to those of apes. The shape of the jaw is now fully parabolic, like that of humans, and the size of the canine teeth is further reduced compared to afarensis.
Australopithecus garhi, is known from a partial skull.
Australopithecus afarensis and africanus, and the other species above, are known as gracile australopithecines, because of their relatively lighter build, especially in the skull and teeth. (Gracile means "slender", and in paleoanthropology is used as an antonym to "robust".) Despite this, they were still more robust than modern humans.
Australopithecus aethiopicus
A. aethiopicus existed between 2.6 and 2.3 million years ago.
Australopithecus robustus
A. robustus had a body similar to that of africanus, but a larger and more robust skull and teeth. It existed between 2 and 1.5 million years ago. The massive face is flat or dished, with no forehead and large brow ridges. The average brain size is about 530 cc. Bones excavated with robustus skeletons indicate that they may have been used as digging tools.
Australopithecus boisei (was called Zinjanthropus boisei)
A. boisei existed between 2.1 and 1.1 million years ago. It was similar to robustus, but the face and cheek teeth were even more massive, some molars being up to 2 cm across. The brain size is very similar to robustus, about 530 cc. A few experts consider boisei and robustus to be variants of the same species.
Australopithecus aethiopicus, robustus and boisei are known as robust australopithecines, because their skulls in particular are more heavily built. They have never been serious candidates for being direct human ancestors. Many authorities now classify them in the genus Paranthropus.
H. habilis, "handy man", was so called because of evidence of tools found with its remains. Habilis existed between 2.4 and 1.5 million years ago. It is very similar to australopithecines in many ways. The face is still primitive, but it projects less than in A. africanus. The back teeth are smaller, but still considerably larger than in modern humans. The average brain size, at 650 cc, is considerably larger than in australopithecines. Brain size varies between 500 and 800 cc, overlapping the australopithecines at the low end and H. erectus at the high end. The brain shape is also more humanlike. The bulge of Broca's area, essential for speech, is visible in one habilis brain cast, and indicates it was possibly capable of rudimentary speech. Habilis is thought to have been about 127 cm (5'0") tall, and about 45 kg (100 lb) in weight, although females may have been smaller.
Habilis has been a controversial species. Originally, some scientists did not accept its validity, believing that all habilis specimens should be assigned to either the australopithecines or Homo erectus. H. habilis is now fully accepted as a species, but it is widely thought that the 'habilis' specimens have too wide a range of variation for a single species, and that some of the specimens should be placed in one or more other species. One suggested species that is accepted by many scientists is Homo rudolfensis, which would contain fossils such as ER 1470.
Homo georgicus: in 2002 a fossils found in Dmanisi, Georgia, seemed intermediate between H. habilis and H. erectus. The fossils are about 1.8 million years old, consisting of three partial skulls and three lower jaws. The brain sizes of the skulls vary from 600 to 780 cc. The height, as estimated from a foot bone, would have been about 1.5 m (4'11"). A partial skeleton was also discovered in 2001 but no details are available on it yet. It is the first trace out of Africa.
H. erectus existed between 1.8 million and 300,000 years ago. Like habilis, the face has protruding jaws with large molars, no chin, thick brow ridges, and a long low skull, with a brain size varying between 750 and 1225 cc. Early erectus specimens average about 900 cc, while late ones have an average of about 1100 cc. The skeleton is more robust than those of modern humans, implying greater strength. Body proportions vary; the Turkana Boy is tall and slender (though still extraordinarily strong), like modern humans from the same area, while the few limb bones found of Peking Man indicate a shorter, sturdier build. Study of the Turkana Boy skeleton indicates that erectus may have been more efficient at walking than modern humans, whose skeletons have had to adapt to allow for the birth of larger-brained infants. Homo habilis and all the australopithecines are found only in Africa, but erectus was wide-ranging, and has been found in Africa, Asia, and Europe. There is evidence that erectus probably used fire, and their stone tools are more sophisticated than those of habilis.
Homo ergaster, some scientists classify some African erectus specimens as belonging to a separate species, Homo ergaster, which differs from the Asian H. erectus fossils in some details of the skull (e.g. the brow ridges differ in shape, and erectus would have a larger brain size). Under this scheme, H. ergaster would include fossils such as the Turkana boy and ER 3733.
Homo antecessor was named in 1977 from fossils found at the Spanish cave site of Atapuerca, dated to at least 780,000 years ago, making them the oldest confirmed European hominids. The mid-facial area of antecessor seems very modern, but other parts of the skull such as the teeth, forehead and browridges are much more primitive. Many scientists are doubtful about the validity of antecessor, partly because its definition is based on a juvenile specimen, and feel it may belong to another species
Homo sapiens (archaic) (also Homo heidelbergensis)
Archaic forms of Homo sapiens first appear about 500,000 years ago. The term covers a diverse group of skulls which have features of both Homo erectus and modern humans. The brain size is larger than erectus and smaller than most modern humans, averaging about 1200 cc, and the skull is more rounded than in erectus. The skeleton and teeth are usually less robust than erectus, but more robust than modern humans. Many still have large brow ridges and receding foreheads and chins. There is no clear dividing line between late erectus and archaic sapiens, and many fossils between 500,000 and 200,000 years ago are difficult to classify as one or the other.
Homo sapiens neanderthalensis (also Homo neanderthalensis)
Neandertal (or as I prefer Neanderthal) man existed between 230,000 and 30,000 years ago. The average brain size is slightly larger than that of modern humans, about 1450 cc, but this is probably correlated with their greater bulk. The brain case however is longer and lower than that of modern humans, with a marked bulge at the back of the skull. Like erectus, they had a protruding jaw and receding forehead. The chin was usually weak. The midfacial area also protrudes, a feature that is not found in erectus or sapiens and may be an adaptation to cold. There are other minor anatomical differences from modern humans, the most unusual being some peculiarities of the shoulder blade, and of the pubic bone in the pelvis. Neandertals mostly lived in cold climates, and their body proportions are similar to those of modern cold-adapted peoples: short and solid, with short limbs. Men averaged about 168 cm (5'6") in height. Their bones are thick and heavy, and show signs of powerful muscle attachments. Neanderthals would have been extraordinarily strong by modern standards, and their skeletons show that they endured brutally hard lives. A large number of tools and weapons have been found, more advanced than those of Homo erectus. Neanderthals were formidable hunters, and are the first people known to have buried their dead, with the oldest known burial site being about 100,000 years old. They are found throughout Europe and the Middle East. Western European Neanderthals usually have a more robust form, and are sometimes called "classic Neanderthals". Neanderthals found elsewhere tend to be less excessively robust.
Homo floresiensis was discovered on the Indonesian island of Flores in 2003 but doesn’t' fit in the evolutionary ladder. Fossils have been discovered from a number of individuals. The most complete fossil is of an adult female about 1 meter tall with a brain size of 417cc. Other fossils indicate that this was a normal size for floresiensis. It is thought that floresiensis is a dwarf form of Homo erectus - it is not uncommon for dwarf forms of large mammals to evolve on islands. H. floresiensis was fully bipedal, used stone tools and fire, and hunted dwarf elephants also found on the island. It could be that this group had a sort of Laron syndrome.
Homo sapiens sapiens (modern)
Modern forms of Homo sapiens first appear in the Pleistocene between 195,000 and 125,000 years ago. Modern humans have an average brain size of about 1350 cc. The forehead rises sharply, eyebrow ridges are very small or more usually absent, the chin is prominent, and the skeleton is very gracile. About 40,000 years ago, with the appearance of the Cro-Magnon culture, tool kits started becoming markedly more sophisticated, using a wider variety of raw materials such as bone and antler, and containing new implements for making clothing, engraving and sculpting. Fine artwork, in the form of decorated tools, beads, ivory carvings of humans and animals, clay figurines, musical instruments, and spectacular cave paintings appeared over the next 20,000 years.
Even within the last 100,000 years, the long-term trends towards smaller molars and decreased robustness can be discerned. The face, jaw and teeth of Mesolithic humans (about 10,000 years ago) are about 10% more robust than ours. Upper Paleolithic humans (about 30,000 years ago) are about 20 to 30% more robust than the modern condition in Europe and Asia. These are considered modern humans, although they are sometimes termed "primitive". Interestingly, some modern humans (aboriginal Australians) have tooth sizes more typical of archaic sapiens. The smallest tooth sizes are found in those areas where food-processing techniques have been used for the longest time. This is a probable example of natural selection which has occurred within the last 10,000 years.
It seems that the appearance and success of man gave a setback to the other type of apes: the various species of ape existing to day are, counted all together adding up to less than 200,000 individuals. It seems also that another big problem is not only the diminishing environment, as humans grew more and more but also a not too much efficient strategy in reproduction.
Independently from how much well Homo Sapiens Sapiens thrived in his origins the human population was reduced to a small number of breeding pairs - no more than 10,000, and possibly as few as 1,000 - resulting in a very small residual gene pool, according to the "Toba catastrophe theory", that assumes that of a massive volcanic eruption severely reduced the human population: this may have occurred around 70,000-75,000 years ago when the Toba caldera in Indonesia underwent an eruption of category 8 (or "mega-colossal") on the Volcanic Explosivity Index. This released energy equivalent to about 1 gigaton of TNT (4.2 EJ), fifty times greater than the 1980 eruption of Mount St. Helens, and twenty times greater than the largest man-made explosion, the October 30, 1961 detonation of the Soviet Union's "Tsar Bomb" a thermonuclear device. When Toba volcano in western Sumatra erupted 73,000 +/- 4000 years ago it was (and still is) the largest volcanic cataclysm to have taken place on planet earth for the last 28 million years.
According to this theory, the Toba explosion reduced the average global temperature by 5 degrees Celsius (9 degrees Fahrenheit) for several years and may have triggered an ice age. It's proposed that this massive environmental change created population bottlenecks in the species that existed at the time; this in turn accelerated differentiation of the isolated human populations, eventually leading to the extinction of all the other human species except for the two branches Neanderthals (H. neanderthalensis) already adapted to cold climates, in Eurasia and modern humans (H. sapiens) in Africa, where the impact of cooling was less hard. Eventually humans once again fanned out from Africa when the climate and other factors permitted.
They migrated first to Arabia and India and onwards to Indochina and Australia, and later to the Middle East and what would become the Fertile Crescent following the end of the Würm glaciation period (110,000-10,000 years ago).
The diffusion of man on the surface of the planet was a very long walk. Apart Antarctica and some little island all Earth was in the end populated, but it took a lot of time. The last group of hunter gathers arrived in the last place of human expansion when in other pat of the world empires had been established and had fallen. For clarity we give an account of the diffusion prior of relating about "civilization".
We made here a distinction between culture and civilization. Culture (from the Latin cultura stemming from colere, meaning "to cultivate") generally refers to patterns of human activity and the symbolic structures that give such activities significance and importance. Cultures can be "understood as systems of symbols and meanings that even their creators contest, that lack fixed boundaries, that are constantly in flux, and that interact and compete with one another". Culture can be defined as all the ways of life including arts, beliefs and institutions of a population that are passed down from generation to generation. Culture has been called "the way of life for an entire society." As such, it includes codes of manners, dress, language, religion, rituals, norms of behavior such as law and morality, and systems of belief as well as the art. In the opinion of the writer of this note every species that has a passing of behavior from a generations to another (also the mother cat teaching to catch mice at the kittens has a culture). All ancient species of humanoids an all the ancient groups of man had a culture.
A civilization or civilisation is a society or culture group normally defined as a complex society characterized by the practice of agriculture and settlement in cities. Compared with other cultures, members of a civilization are organized into a diverse division of labour and an intricate social hierarchy.
About 1,000,000 years ago walking a little space every generation humans arrived from Africa to China. Half million years after crossing the Caucasus they arrived in Europe. Other parts of the world required longer time: Australia was reached 40,000 ago, Papua 5,000 years after, during a glacial period that lowered the level of the sea. An area like Siberia required that mankind reached a cultural level enabling it to cope with cold climate 20 thousand years ago, from Siberia to North America took 8,000 years, and the crossing of the continent from Alaska to Terra del Fuego only a couple of millennia. The last areas to be occupied by primitive population were the Polynesian islands, Hawaii in the year 500 C.E. New Zealand 1000 C.E. and the last Chatham Island about
1350 C.E. Other places as the Mauritius Island was colonized later but civilized people did this and so is not to be thought as diffusion on man, but as colonization.
All in all about 10,000 years ago all the major part of the word had seen humans, Greenland included. It was a very diffuse but disperse presence. An informed guess sets the number of people that could live as hunter gatherers at about 5, 10 millions of individuals (to day Mumbay alone has 13,662,885 inhabitants). But about at that time something happened and the human story stopped to be natural history and became something different.
The first part deal with “Natural History”, the second with “Political History” Natural history is defined as the scientific research about plants or animals and other objects, as the planets and stars, leaning more towards the observational than experimental methods of study, and encompasses more research that is published in magazines than in academic journals. The name derives from Naturalis Historia (Latin for "Natural History") is an encyclopedia written circa AD 77 by Pliny the Elder. DISCLAIMER: the entry is a COMPILATION of what I think is notably between the things I red so a lot of this you can find around I do not quote the sources only because they would be longer tan the text himself! This phrase is intended as acknowledgments to the entire world of science. For simplicity I use plain text instead of a formatted text.
The term "universe" may be used in slightly different contextual senses, denoting such concepts as the cosmos, the world or Nature. Lucretius the first known author that used the word did it in the sense "everything rolled into one, everything combined into one".
Universe (or the World) is here defined and used as "everything that physically exists": the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them. However, the Astronomical observations indicate that the universe is 11 to 20 billion (the best bet is 13.73 ± 0.12 billion) years old and at least 93 billion light years across, while 3×10^52 kg is the Mass of the observable universe. It may seem paradoxical that two point can be separated by a distance that is more tan seven times the years of the universe; however, this - we are granted - is a simple consequence of general relativity.
There are three elements constituting the universe (space-time, matter-energy, and physical law) that correspond roughly to the ideas of Aristotle. In his book The Physics (Greek word for Nature from which we derive the word "physics"), Aristotle divided everything into three roughly analogous elements: matter (the stuff of which the universe is made), form (the arrangement of that matter in space) and change (how matter is created, destroyed or altered in its properties, and similarly, how form is altered). Other idea that discern natura naturans (the active principles governing the universe) from natura naturata, the passive elements upon which the former act, as in Averroes and Spinoza do not interest us.
The universe is believed to be mostly composed of dark energy and dark matter, both of which are poorly understood at present. Only about 4% of mass of the universe is ordinary matter. A relatively small perturbation, so to speak.
The early universe is supposed to be knowable (also theoretically) only from a certain point of tome forward, called the Plank Time, the preceding period being called "The Age of St. Augustine".
The phrase "Augustinian Era" proposed in 1952, by George Gamow, is meant to convey the idea that the known laws of physics break down in a gravitational singularity of infinite density at the time zero of the Big Bang, so that according to Albert Einstein's general theory of relativity there were no times prior to that point. However, physicists believe that general relativity becomes incompatible with quantum mechanics at the Planck scale, so that the predictions of general relativity cannot be trusted before the Planck era when energies and temperatures reached the Planck scale, and that we need a theory of quantum gravitation before we can say anything about times before the Planck era.
The Planck epoch followed The Age of St. Augustine, up to 10^-43 seconds after the Big Bang: during this time, if supersymmetry theory is correct, the four fundamental forces - electromagnetism, weak nuclear force, strong nuclear force and gravitation - all had the same strength, so they are possibly unified into one fundamental force. Little is known about this epoch, and different theories propose different scenarios. The size of universe is less than the size of an atom, at this point.
Then follows the Grand Unification Epoch, lasting between 10^-43 seconds and 10^-36 seconds after the Big Bang, when as the universe expands and cools from the Planck epoch, gravitation begins to separate from the fundamental gauge interactions: electromagnetism and the strong and weak nuclear forces. Physics at this scale may be described by a grand unified theory in which the gauge group of the Standard Model is embedded in a much larger group, which is broken to produce the observed forces of nature. Eventually, the grand unification is broken as the strong nuclear force separates from the electroweak force. This occurs as soon as inflation does. According to some theories, this should produce magnetic monopoles. Unification of the strong and electroweak forces means that the only particle expected at this time is the Higgs boson.
Between 10^-36 seconds and 10^-12 seconds after the Big Bang is the Electroweak Epoch. Now the temperature of the universe is low enough (10^28K) to separate the strong force from the electroweak force (the name for the unified forces of electromagnetism and the weak interaction). This phase transition triggers a period of exponential expansion known as cosmic inflation. After inflation ends, particle interactions are still energetic enough to create large numbers of exotic particles, including W and Z bosons and Higgs bosons.
Between 10^-36 seconds and 10^-32 seconds after the Big Bang the temperature, and therefore the time, at which cosmic inflation occurs is not known for certain. And this period is termed The Inflationary Epoch: during inflation, the universe is flattened (its spatial curvature is critical) and the universe enters a homogeneous and isotropic rapidly expanding phase in which the seeds of structure formation are laid down in the form of a primordial spectrum of nearly-scale-invariant fluctuations. Some energy from photons becomes virtual quarks and hyperons, but these particles decay quickly. One scenario suggests that prior to cosmic inflation, the universe was cold and empty, and the immense heat and energy associated with the early stages of the big bang was created through the phase change associated with the end of inflation.
A Reheating phase seems to be associate at the inflationary period. During reheating, the exponential expansion that occurred during inflation ceases and the potential energy of the inflation field decays into a hot, relativistic plasma of particles. If grand unification is a feature of our universe, then cosmic inflation must occur during or after the grand unification symmetry is broken, otherwise magnetic monopoles would be seen in the visible universe. At this point, the universe is dominated by radiation; quarks, electrons and neutrinos form. Someone think the size of the universe as big as a toy ball, now.
No known physics can explain the fact that there are in the universe so many more particles called baryons than antibaryons.
Supersymmetry breaking (if supersymmetry is a property of our universe) was followed by The Quark epoch (between 10^-12 seconds and 10-6 seconds) and by (between 10^-6 seconds and 1 second after the Big Bang the Hadron epoch and Lepton epoch between 1 second and 3 minutes after the Big Bang.
The majority of hadrons and anti-hadrons annihilate each other at the end of the hadron epoch, leaving leptons and anti-leptons dominating the mass of the universe. Approximately 3 seconds after the Big Bang the temperature of the universe falls to the point where new lepton/anti-lepton pairs are no longer created and most leptons and anti-leptons are eliminated in annihilation reactions, leaving a small residue of leptons.
More or less at this point the whole globe himself was almost behaving as an avalanche rolling down the slope of a mountain, at least as the laws of physics are concerned. And now the whole that exist is approximately the size of our Solar System!
After most leptons and anti-leptons are annihilated at the end of the lepton epoch the energy of the universe is dominated by photons. These photons are still interacting frequently with charged protons, electrons and (eventually) nuclei, and continue to do so for the next 300,000 years. Now between 3 minutes and 380,000 years after the Big Bang the Universe is living the Photon epoch
The next quarter of an hour meaning from 3 minutes to 20 minutes after the Big Bang the Nucleosynthesis occours. Now the temperature of the universe had fallen to the point where atomic nuclei can begin to form. Protons (hydrogen ions) and neutrons begin to combine into atomic nuclei in the process of nuclear fusion. However, nucleosynthesis only lasts for about seventeen minutes, after which time the temperature and density of the universe has fallen to the point where nuclear fusion cannot continue. At this time, there is about three times more hydrogen than helium-4 (by mass) and only trace quantities of other nuclei.
At this time, the densities of non-relativistic matter (atomic nuclei) and relativistic radiation (photons) are equal. The Jeans length, which determines the smallest structures that can form (due to competition between gravitational attraction and pressure effects), begins to fall and perturbations, instead of being wiped out by radiation free-streaming, can begin to grow in amplitude.
Obviously one can be very surprised of the speeding of the phenomenon, but could be that in this form of universe our time does not make sense
The Age of Recombination. Hydrogen and helium atoms begin to form and the density of the universe falls. This is thought to have occurred somewhere between 240,000 and 310,000 years after the Big Bang. Hydrogen and helium are at the beginning ionized, i.e. no electrons are bounded to the nuclei, which are therefore electrically charged (+1 and +2 respectively). As the universe cools down, the electrons get captured by the ions making them neutral. This process is relatively fast (actually faster for the helium than for the hydrogen) and is known as recombination. At the end of recombination, most of the atoms in the universe are neutral, therefore the photons can now travel freely: the universe has become transparent. The photons emitted right after the recombination, that can therefore travel undisturbed, are those that we see in the cosmic microwave background (CMB) radiation. Therefore the CMB is a picture of the universe at the end of this epoch.
Structure formation in the big bang model proceeds hierarchically, with smaller structures forming before larger ones. The first structures to form are quasars, which are thought to be bright, early active galaxies, and population III stars.
The first stars, most likely Population III stars, form and start the process of turning the light elements that were formed in the Big Bang (hydrogen, helium and lithium) into heavier elements. However, as of yet there have been no observed Population III stars, which leaves their formation a mystery.
Large volumes of matter collapse to form a galaxy. Population II stars are formed early on in this process, with Population I stars formed later.
Based upon the emerging branch of astronomy, nucleocosmochronology, the Galactic thin disk of the Milky Way is estimated to have been formed 8.3 ± 1.8 billion years ago.
Gravitational attraction pulls galaxies towards each other to form groups, clusters and superclusters. The Virgo Supercluster (or Local Supercluster) is the galactic supercluster that contains the Local Group, the latter containing, in its turn, the Milky Way and Andromeda galaxies. As the best current data estimate the age of the universe today as 13.7 billion years since the big bang the matter in our supercluster was a sample of the 5 billion years old universe. Since the expansion of the universe appears to be accelerating (due more than other to dark energy), superclusters are likely to be the largest structures that will ever form in the universe. As he present accelerated expansion prevents any more inflationary structures entering the horizon and prevents new gravitationally bound structures from forming.
Finally, objects on the scale of our solar system form. Our sun (The Sun) formed roughly 5 billion years ago, or roughly 8 to 9 billion years after the big bang, about 3 billions after the local cluster is a late-generation star, incorporating the debris from many generations of earlier stars.
The Solar System in broad terms, consist of the Sun, four inner planets, in order of their distances from the Sun, the "terrestrial" planets are: Mercury, Venus, the Earth and Mars. An asteroid belt composed of small rocky bodies, Ceres the largest object in the asteroid belt separate this four from the four gas giant outer planets (or Jovians): Jupiter, Saturn, Uranus and Neptune and a second belt, the Kuiper belt, composed of icy objects. Pluto, Makemake are the largest Kuiper belt objects. Eris is the largest known object in the scattered disc, beyond the Kuiper belt. Outward are: the scattered disc, the heliopause, and ultimately the hypothetical Oort cloud.
Six of the eight planets and two of the dwarf planets are in turn orbited by natural satellites, usually termed "moons" after Earth's Moon, and each of the outer planets is encircled by planetary rings of dust and other particles, Saturn’s rings the most famous. All the "true" planets except Earth, and a lot of the other objects, are named after deities from Greco-Roman mythology.
The principal component of the Solar System is the Sun, a main sequence G2 star that contains 99.86 percent of the system's known mass and dominates it gravitationally. Jupiter and Saturn, the Sun's two largest orbiting bodies, account for more than 90 percent of the system's remaining mass.
Jupiter is just about as large in diameter as a gas planet can be. If more material were to be added, it would be compressed by gravity such that the overall radius would increase only slightly. A star can be larger only because of its internal (nuclear) heat source, but Jupiter would have to be at least 80 times more massive to become a star. Also if not a star Jupiter radiates more energy into space than it receives from the Sun, in this respect is the only other source of energy in the system: the interior of Jupiter is hot: the core is probably about 20,000 K, the heat being generated by the Kelvin-Helmholtz mechanism, the slow gravitational compression of the planet. (Jupiter does NOT produce energy by nuclear fusion as in the Sun; it is much too small and hence its interior is too cool to ignite nuclear reactions.)
The form of the system is ruled and determined by the energy of the Sun and the gravity law (the attractive force of Jupiter seems to be responsible for the asteroid belt not forming a planet.
The most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic while comets and Kuiper belt objects are usually at significantly greater angles to it.
The Solar System is believed to have formed according to the nebular hypothesis, which holds that it emerged from the gravitational collapse of a giant molecular cloud 4-6 billions years ago. This initial cloud was likely several light-years across and probably birthed several stars. Studies of ancient meteorites reveal traces of elements only formed in the hearts of very large exploding stars, indicating that, with the most probability, the Sun formed within a star cluster, and in range of a number of nearby supernovae explosions. The shock wave from these supernovae may have triggered the formation of the Sun by creating regions of overdensity in the surrounding nebula, allowing gravitational forces to overcome internal gas pressures and cause the collapse.
The region that would become the Solar System, known as the pre-solar nebula, had a diameter of between 7000 and 20,000 Astronomical Units (AU, an AU equals the mean distance between the Earth and the Sun - approximately 150 million km or 93 million miles) and a mass just over that of the Sun. As the nebula collapsed, conservation of angular momentum made it rotate faster. As the material within the nebula condensed, the atoms within it began to collide with increasing frequency. The centre, where most of the mass collected, became increasingly hotter than the surrounding disc. As gravity, gas pressure, magnetic fields, and rotation acted on the contracting nebula, it began to flatten into a spinning protoplanetary disc with a diameter of roughly 200 AU and a hot, dense protostar at the centre.
Studies of T Tauri stars, young, pre-fusing solar mass stars believed to be similar to the Sun at this point in its evolution, show that discs of pre-planetary matter often accompany them. These discs extend to several hundred AU and reach only a thousand Kelvin at their hottest.
Within 50 million years, the pressure and density of hydrogen in the centre of the collapsing nebula became great enough for the proto-sun to begin thermonuclear fusion. The temperature, reaction rate, pressure, and density increased until hydrostatic equilibrium was achieved, with the thermal energy countering the force of gravitational contraction. At this point the Sun became a full-fledged main sequence star.
From the remaining cloud of gas and dust (the "solar nebula"), the various planets formed. They are believed to have formed by accretion: the planets began as dust grains in orbit around the central protostar; then gathered by direct contact into clumps between one and ten meters in diameter; then collided to form larger bodies (planetesimals) of roughly 5 km in size; then gradually increased by further collisions at roughly 15 cm per year over the course of the next few million years.
The inner Solar System was too warm for volatile molecules like water and methane to condense, and so the planetesimals which formed there were relatively small (comprising only 0.6% the mass of the disc) and composed largely of compounds with high melting points, such as silicates and metals. These rocky bodies eventually became the terrestrial planets. Farther out, the gravitational effects of Jupiter made it impossible for the protoplanetary objects present to come together, leaving behind the asteroid belt.
Farther out still, beyond the frost line, where more volatile icy compounds could remain solid, Jupiter and Saturn became the gas giants. Uranus and Neptune captured much less material and are known as ice giants because their cores are believed to be made mostly of ices (hydrogen compounds).
Once the young Sun began producing energy, the solar wind blew the gas and dust in the protoplanetary disk into interstellar space and ended the growth of the planets. T Tauri stars have far stronger stellar winds than more stable, older stars.
Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the Earth, Planet Earth, the World, and Terra, home to millions of species, including humans; Earth is the only place in the universe where life is known to exist.
Scientific evidence indicates that the planet formed 4.54 billion years ago, and life appeared on its surface within a billion years. Since then, Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet, enabling the proliferation of aerobic organisms as well as the formation of the ozone layer which, together with Earth's magnetic field, blocks harmful radiation, permitting life on land.
Earth's outer surface is divided into several rigid segments, or tectonic plates, that gradually migrate across the surface over periods of many millions of years. About 71% of the surface is covered with salt-water oceans, the remainder consisting of continents and islands; liquid water, necessary for all known life, is not known to exist on any other planet's surface. Earth's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid iron inner core.
Earth interacts with other objects in outer space, including the Sun and the Moon. At present, Earth orbits the Sun once for every roughly 366.26 times it rotates about its axis. This length of time is a sidereal year, which is equal to 365.26 solar days. The Earth's axis of rotation is tilted 23.4° away from the perpendicular to its orbital plane, producing seasonal variations on the planet's surface with a period of one tropical year (365.24 solar days). Earth's only known natural satellite, the Moon, which began orbiting it about 4.53 billion years ago, provides ocean tides, stabilizes the axial tilt and gradually slows the planet's rotation. A cometary’s bombardment during the early history of the planet played a role in the formation of the oceans. Later, asteroid impacts caused significant changes to the surface environment. Earth and the other planets in the Solar System formed 4.54 billion years ago, as previously told, the Moon formed soon afterwards, possibly as the result of a Mars-sized object (sometimes called Theia) with about 10% of the Earth's mass impacting the Earth in a glancing blow: some of this object's mass would have merged with the Earth and a portion would have been ejected into space, but enough material would have been sent into orbit to form the Moon.
Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice and liquid water delivered by asteroids and the larger proto-planets, comets, and trans-Neptunian objects produced the oceans. The highly energetic chemistry is believed to have produced a self-replicating molecule around 4 billion years ago, and half a billion years later, the last common ancestor of all life existed. The details of the origin of life are unknown, though the broad principles have been established. Two schools of thought regarding the origin of life have been proposed. The first suggests that organic components may have arrived on Earth from space (see "Panspermia"), while the other argues for terrestrial origins. In the long run the mechanisms by which life would initially arise are nevertheless held to be similar, so the first hypothesis is just a complication more. If life arose on Earth, the timing of this event is highly speculative-perhaps it arose around 4 billion years ago. In the energetic chemistry of early Earth, a molecule (or even something else) gained the ability to make copies of itself-the replicator. The nature of this molecule is unknown, its function having long since been superseded by life's current replicator, DNA. In making copies of itself, the replicator did not always perform accurately: some copies contained an "error." If the change destroyed the copying ability of the molecule, there could be no more copies, and the line would "die out." On the other hand, a few rare changes might make the molecule replicate faster or better: those "strains" would become more numerous and "successful" hence evolution arose. As choice raw materials ("food") became depleted, strains, which could exploit different materials, or perhaps halt the progress of other strains and steal their resources, became more numerous.
Several different models have been proposed explaining how a replicator might have developed. Different replicators have been posited, including organic chemicals such as modern proteins, nucleic acids, phospholipids, and crystals. There is currently no method of determining which of these models, if any, closely fits the origin of life on Earth. One of the older theories, and one which has been worked out in some detail, will serve as an example of how this might occur. The high energy from volcanoes, lightning, and ultraviolet radiation could help drive chemical reactions producing more complex molecules from simple compounds such as methane and ammonia, among these were many of the relatively simple organic compounds that are the building blocks of life. As the amount of this "organic soup" increased, different molecules reacted with one another. Sometimes more complex molecules would result (perhaps clay provided a framework to collect and concentrate organic material). All this continued for a very long time, with reactions occurring more or less at random, until by chance there arose a new molecule: the replicate. This had the bizarre property of promoting the chemical reactions that produced a copy of itself, and evolution began properly. Biologists have tentatively traced the most recent common ancestor of all life to an aquatic microorganism that lived in extremely high temperatures many biologists hypothesize that this step led to an "RNA world" in which RNA did many jobs, storing genetic information, copying itself, and performing basic metabolic functions. Eventually DNA took over the function of the replicator at some point so that now (with the exception of some viruses and prions) all known life use DNA as replicator, in an almost identical manner.
It was bacteria that gave life its initial foothold, and it was bacteria by the trillions that engineered the planet for our use, taking in carbon dioxide and giving off oxygen, day in and day out for billions of years until there was enough oxygen in the atmosphere to support larger life.
The oldest known fossilized prokaryotes were laid down approximately 3.5 billion years ago, only about 1 billion years after the formation of the earth's crust. Even today, prokaryotes are perhaps the most successful and abundant life forms. Eukaryotes only formed later, from endosymbiosis of multiple prokaryote ancestors. The prokaryotes are divided into two domains: the bacteria and the archaea. Archaea are a newly appointed domain of life. These organisms were originally thought to live only in inhospitable conditions such as extremes of temperature, pH, and radiation but have since been found in all types of habitats. The oldest known fossil eukaryotes are about 1.7 billion years old. However, some genetic evidence suggests eukaryotes appeared as early as 3 billion years ago.
The biochemical capacity to use water as the source for electrons in photosynthesis evolved once, in a common ancestor of extant cyanobacteria. The geological record indicates that this transforming event took place early in Earth's history, at least 2450-2320 million years ago, and possibly much earlier. The development of photosynthesis allowed the Sun's energy to be harvested directly by life forms; the resultant oxygen accumulated in the atmosphere and resulted in a layer of ozone (a form of molecular oxygen [O3]) in the upper atmosphere. The incorporation of smaller cells within larger ones resulted in the development of complex cells called eukaryotes. True multicellular organisms formed as cells within colonies became increasingly specialized. Aided by the absorption of harmful ultraviolet radiation by the ozone layer, life colonized the surface of Earth.
Beginning with almost no dry land, the total amount of surface lying above the oceans has steadily increased. During the past two billion years, for example, the total size of the continents has doubled. As the surface continually reshaped itself, over hundreds of millions of years, continents formed and broke up. The continental plaques migrate across the surface of the globe, occasionally combining to form a super continent. Roughly 750 million years ago, the earliest known supercontinent, Rodinia, began to break apart. The continents later recombined to form Pannotia, 600-540 millions years ago, then finally Pangaea, which broke apart 180 millions years ago.
Since the 1960s, it has been hypothesized that severe glacial action between 750 and 580 millions years ago, during the Neoproterozoic, covered much of the planet in a sheet of ice. This hypothesis has been termed "Snowball Earth", and is of particular interest because it preceded the Cambrian explosion, when multicellular life forms began to proliferate.
For most of the nearly 4 billion years that life has existed on Earth, evolution produced little beyond bacteria, plankton, and multi-celled algae. But beginning about 600 million years ago in the Precambrian, the fossil record speaks of more rapid change. First, there was the rise and fall of mysterious creatures of the Ediacaran fauna, named for the fossil site in Australia where they were first discovered. Some of these animals may have belonged to groups that survive today, but others don't seem at all related to animals we know. Then, between about 570 and 530 million years ago, another burst of diversification occurred, with the eventual appearance of the lineages of almost all animals living today. This stunning and unique evolutionary flowering is termed the "Cambrian explosion," taking the name of the geological age in whose early part it occurred. But it was not as rapid as an explosion: the change seems to have happened in a range of about 30 million years, and some stages took 5 to 10 million years.
It's important to remember that what we call "the fossil record" is only the available fossil record. In order to be available to us, the remains of ancient plants and animals have to be preserved first, and this means that they need to have fossilizable parts and to be buried in an environment that will not destroy them. It has long been suspected that the sparseness of the pre-Cambrian fossil record reflects these two problems. First, organisms may not have sequestered and secreted much in the way of fossilizable hard parts; and second, the environments in which they lived may have characteristically dissolved those hard parts after death and recycled them. An exception was the mysterious "small shelly fauna" -- minute shelled animals that are hard to categorize -- that left abundant fossils in the early Cambrian. Recently, minute fossil embryos dating to 570 million years ago have also been discovered. Even organisms that hadn't evolved hard parts, and thus didn't leave fossils of their bodies, left fossils of the trails they made as they moved through the Precambrian mud. Life was flourishing long before the Cambrian "explosion".
The best record of the Cambrian diversification is the Burgess Shale in British Columbia. Laid down in the middle-Cambrian, when the "explosion" had already been underway for several million years, this formation contains the first appearance in the fossil record of brachiopods, with clamlike shells, as well as trilobites, mollusks, echinoderms, and many odd animals that probably belong to extinct lineages. They include Opabinia, with five eyes and a nose like a fire hose, and Wiwaxia, an armored slug with two rows of upright scales. The question of how so many immense changes occurred in such a short time is one that stirs scientists. Why did many fundamentally different body plans evolve so early and in such profusion? Some point to the increase in oxygen that began around 700 million years ago, providing fuel for movement and the evolution of more complex body structures. Others propose that an extinction of life just before the Cambrian opened up ecological roles, or "adaptive space," that the new forms exploited. External, ecological factors like these were undoubtedly important in creating the opportunity for the Cambrian explosion to occur, but internal, genetic factors were also crucial. Recent research suggests that the period prior to the Cambrian explosion saw the gradual evolution of a "genetic tool kit" of genes that govern developmental processes. Once assembled, this genetic tool kit enabled an unprecedented period of evolutionary experimentation, and competition. Many forms seen in the fossil record of the Cambrian disappeared without trace. Once the body plans that proved most successful came to dominate the biosphere, evolution never had such a free hand again, and evolutionary change was limited to relatively minor tinkering with the body plans that already existed.
Interpretations of this critical period are subject of lively debate among scientists like Stephen Jay Gould of Harvard University and Simon Conway Morris of Cambridge University. Gould emphasizes the role of chance. He argues that if one could "rerun the tape" of that evolutionary event, a completely different path might have developed and would likely not have included a humanlike creature. Morris, on the other hand, contends that the environment of our planet would have created selection pressures that would likely have produced similar forms of life to those around us, including humans.
At this point the classifications of times became impressive and complicated
There are Eras, Periods, Subperiods and Epochs now will follows a series of epoch and periods an their main fact.
505 millions years ago is the Ordovician period. Invertebrates are dominant, but the first fishes appear.
Mesozoic (from 251.0 to 65.5 million years ago, meaning from Greek and means "middle life", as it is an era of geologic time between the Paleozoic and the Cenozoic.
251.0 to 199.6 million years ago Triassic sees the emerging of dinosaurs and also egg-laying mammals. From about 280-230 million years ago, (Late Paleozoic Era until the Late Triassic) the continent we now know as North America was continuous with Africa, South America, and Europe, archosaurs (forbearers of crocodiles dinosaurs and birds first appeared in the late Permian more or less at this point. Pangea first began to be torn apart when a three-pronged fissure grew between Africa, South America, and North America. There were three major phases in the break-up of Pangaea. The first phase began in the Early-Middle Jurassic, when Pangaea created a rift from the Tethys Ocean in the east and the Pacific in the west. The rifting took place between North America and Africa, and produced multiple failed rifts. The rift resulted in a new ocean, the Atlantic Ocean. This first division was important because about at this time in the southern continent 213 millions years ago developed the Marsupial mammals. This is the Jurassic 199.6 to 145.5 million years ago, in which the dinosaurs outpaced mammal in evolution becoming the most visible form of life on Earth
In the Mesozoic (145.5 to 65.5 million years ago) Cretaceous Dinosaurs reach their peak, while primitive placental mammals appeared. This group appears to be original of the north hemisphere, where they outpaced the marsupials. Mammals and near-mammals expanded out of the nocturnal insectivore niche from the mid Juraassic onwards. The traditional view is that: mammals only took over the medium- to large-sized ecological niches in the Cenozoic, after the extinction of the dinosaurs; but then they diversified very quickly, for example the earliest known bat dates from about 50 million years ago, only 15 million years after the extinction of the dinosaurs.
Following the Cambrian explosion, about 535 millions years ago, there have been five mass extinctions. The last extinction event occurred 65 millions years ago, when a meteorite collision probably triggered the extinction of the (non-avian) dinosaurs and other large reptiles, but spared small animals such as mammals, that profited of the disappearance of the big reptiles.
Over the past 65 million years, mammalian life has diversified, conquering every corner of the planet an in many cases topping the food ladder.
Several millions years ago, an African ape-like animal gained the ability to stand upright. This enabled tool use and encouraged communication that provided the nutrition and stimulation needed for a larger brain and a very different rate of reproduction from the other apelike species. The development of agriculture, and then civilization, allowed humans to influence the Earth in a short time span as no other life form had, affecting both the nature and quantity of other life forms. And will be summarized below.
The present pattern of ice ages began about 40 millions years ago, then intensified during the Pleistocene about 3 millions years ago. The Polar Regions have since undergone repeated cycles of glaciation and thaw, repeating every 40-100,000 years. The last ice age ended 10,000 years ago. 2000 years later civilization began.
We are now at just a little over the half of the proposed length of this writing. History of life on Earth account more or less for one fourth of the time but the history of men just 0.0036496%. Of course it's only our pride that account for its, importance.
We must not forget that although what we usually see are the big animals, T-Rex, elephants and whales, lions, cows and man the big Phylun is the one called Arthropoda the major group arthropods are the Insects (Class Insecta) that are a major group of and the most diverse group of animals on the Earth, with over a million described species-more than half of all known living organisms with estimates of undescribed species as high as 30 million, thus potentially representing over 90% of the differing life forms on the planet. Insects may be found in nearly all environments on the planet, although only a small number of species occur in the oceans, a habitat dominated by another arthropod group, the crustaceans.
There are approximately 5,000 dragonfly species, 2,000 praying mantises, 20,000 grasshoppers, 170,000 butterflies and moth, 120,000 fly, 82,000 true bug, 360,000 beetle, and 110,000 bees, wasp and ant species described to date. Estimates of the total number of current species, including those not yet known to science, range from two million to fifty million, with newer studies favouring a lower figure of about six to ten million. Adult modern insects range in size from a 0.139 mm (0.00547 in) firefly (Dicopomorpha echmepterygis) to a 55.5 cm (21.9 in) long stick insect (Phobaeticus serratipes). The heaviest documented insect was a Giant Weta of 70 g (21/2 oz), but other possible candidates include the Goliath beetles Goliathus goliatus, Goliathus regius and Cerambycid beetles such as Titanus giganteus, though no one is certain which is truly the heaviest.
And also in the mammalian group we tend to underestimate the little one, as mice, until they became the essential cause of the black death of a famine. Dealing with the adoption of agriculture we will return to this topic.
Now we simply introduce the R-K concept.
Reproductive strategies can be classified into two major types: r and k strategies. Species, which practice r-strategies usually, emphasize gamete production, mating behavior, low parental care, and high reproductive rates. Species, which practice k-strategies, conversely emphasize high parental care; lower reproductive rates, resource acquisition and a higher degree of social complexity. The k-strategy requires a more complex nervous system as well as larger brains than the primarily r-strategist species do.
In nature, we can see the difference between extreme cases of r and k strategist species. For example, an oyster can produce 500 million eggs a year, while the great apes can reproduce only one infant every 5 or 6 years. Thus, the oyster will have reproduced itself 2500 million times, by the time a great ape will have reproduced itself once. The oyster will not spend any time "parenting" over its offspring, while the great ape will put much time and energy into nurturing their offspring. And also little mammalian are on the r side.
While primates in general are the most k-strategist of all of the species, there still remain differences between them. For example, a lemur is more r-strategist than a gorilla. In fact, going across the primate spectrum, research has shown that primates become more k-strategist with increasing size, and so they born less babies. An exception seems to be the human ape, that as a faster reproductive rate, the fact will be discussed below.
As for today there are SEVEN extant apes: Gibbon, Siamang, Orangutan, Gorilla, Chimpanzee, Bonobo, ...and... Human (aka Homo sapiens sapiens).
But it was not always so. Apes are the members of the Hominoidea superfamily of primates, which includes humans. Under the current classification system there are two families of hominoids: the family Hylobatidae consists of 4 genera and 13 species of gibbons, including the Lar Gibbon and the Siamang, collectively known as the lesser apes. The family Hominidae consisting of orangutans, gorillas, chimpanzees, and humans, collectively known as the great apes.
A few other primates, such as the Barbary Ape, have the word "ape" in their common names (usually to indicate lack of a tail), but they are not regarded as true apes. All the Apes belong to the Primates order. The Primates order is divided informally into three main groupings: prosimians, monkeys of the New World, and monkeys and apes of the Old World. Primates appeared about 63 million years ago, as soon there were no more dinosaurs around, it seems. The time of the split between humans and living apes used to be thought to have occurred 15 to 20 million years ago, or even up to 30 or 40 million years ago. Some apes occurring within that time period, such as Ramapithecus, used to be considered as hominids, and possible ancestors of humans. Later fossil finds indicated that Ramapithecus was more closely related to the orang-utan, and new biochemical evidence indicated that the last common ancestor of hominids and apes occurred between 5 and 10 million years ago, and probably in the lower end of that range. Ramapithecus therefore is no longer considered a hominid.
Hominid Species
The species here are listed roughly in order of appearance in the fossil record (note that this ordering is not meant to represent an evolutionary sequence), except that the robust australopithecines are kept together. Each name consists of a genus name (e.g. Australopithecus, Homo), which is always capitalized, and a specific name (e.g. africanus, erectus), which is always in lower case. Within the text, genus names are often omitted for brevity. Each species has a type specimen that was used to define it.
Sahelanthropus tchadensis, fossils discovered in Chad in Central Africa. It is the oldest known hominid or near-hominid species, dated at between 6 and 7 million years old. The skull has a very small brain size of approximately 350 cc. It is not known whether it was bipedal. So it is close to the common ancestor of humans and chimpanzees.
Orrorin tugenensis. In western Kenya. The fossils include fragmentary arm and thighbones, lower jaws, and teeth and were discovered in deposits that are about 6 million years old. Its finders have claimed that Orrorin was a human ancestor adapted to both bipedality and tree climbing, and that the australopithecines are an extinct offshoot.
Ardipithecus ramidus: it was originally dated at 4.4 million years, but has since been discovered to far back as 5.8 million years. Most remains are skull fragments. Indirect evidence suggests that it was possibly bipedal, and that some individuals were about 122 cm (4'0") tall.
Australopithecus anamensis
From Kanapoi in Kenya, and 12 fossils, mostly teeth found in 1988, from Allia Bay in Kenya (Leakey et al. 1995). Anamensis existed between 4.2 and 3.9 million years ago, and has a mixture of primitive features in the skull, and advanced features in the body. There is strong evidence of bipedality, and a lower humerus (the upper arm bone) is extremely humanlike.
Australopithecus afarensis
A. afarensis existed between 3.9 and 3.0 million years ago. Afarensis had an apelike face with a low forehead, a bony ridge over the eyes, a flat nose, and no chin. They had protruding jaws with large back teeth. Cranial capacity varied from about 375 to 550 cc. The skull is similar to that of a chimpanzee, except for the more humanlike teeth. The canine teeth are much smaller than those of modern apes, but larger and more pointed than those of humans, and shape of the jaw is between the rectangular shape of apes and the parabolic shape of humans. However and that is the interesting feature) their pelvis and leg bones far more closely resemble those of modern man, and leave no doubt that they were bipedal (although adapted to walking rather than running). Their bones show that they were physically very strong. Females were substantially smaller than males, a condition known as sexual dimorphism. Height varied between about 107 cm (3'6") and 152 cm (5'0"). The finger and toe bones are curved and proportionally longer than in humans, but the hands are similar to humans in most other details. Most scientists consider this evidence that afarensis was still partially adapted to climbing in trees, others consider it evolutionary baggage.
Kenyanthropus platyops
Found in Kenya with an unusual mixture of features (Leakey et al. 2001). It is aged about 3.5 million years old. The size of the skull is similar to A. afarensis and A. africanus, and has a large, flat face and small teeth.
Australopithecus africanus
A. africanus existed between 3 and 2 million years ago. It is similar to afarensis, and was also bipedal, but body size was slightly greater. Brain size may also have been slightly larger, ranging between 420 and 500 cc. This is a little larger than chimp brains (despite a similar body size), but still not advanced in the areas necessary for speech. The back teeth were a little bigger than in afarensis. Although the teeth and jaws of africanus are much larger than those of humans, they are far more similar to human teeth than to those of apes. The shape of the jaw is now fully parabolic, like that of humans, and the size of the canine teeth is further reduced compared to afarensis.
Australopithecus garhi, is known from a partial skull.
Australopithecus afarensis and africanus, and the other species above, are known as gracile australopithecines, because of their relatively lighter build, especially in the skull and teeth. (Gracile means "slender", and in paleoanthropology is used as an antonym to "robust".) Despite this, they were still more robust than modern humans.
Australopithecus aethiopicus
A. aethiopicus existed between 2.6 and 2.3 million years ago.
Australopithecus robustus
A. robustus had a body similar to that of africanus, but a larger and more robust skull and teeth. It existed between 2 and 1.5 million years ago. The massive face is flat or dished, with no forehead and large brow ridges. The average brain size is about 530 cc. Bones excavated with robustus skeletons indicate that they may have been used as digging tools.
Australopithecus boisei (was called Zinjanthropus boisei)
A. boisei existed between 2.1 and 1.1 million years ago. It was similar to robustus, but the face and cheek teeth were even more massive, some molars being up to 2 cm across. The brain size is very similar to robustus, about 530 cc. A few experts consider boisei and robustus to be variants of the same species.
Australopithecus aethiopicus, robustus and boisei are known as robust australopithecines, because their skulls in particular are more heavily built. They have never been serious candidates for being direct human ancestors. Many authorities now classify them in the genus Paranthropus.
H. habilis, "handy man", was so called because of evidence of tools found with its remains. Habilis existed between 2.4 and 1.5 million years ago. It is very similar to australopithecines in many ways. The face is still primitive, but it projects less than in A. africanus. The back teeth are smaller, but still considerably larger than in modern humans. The average brain size, at 650 cc, is considerably larger than in australopithecines. Brain size varies between 500 and 800 cc, overlapping the australopithecines at the low end and H. erectus at the high end. The brain shape is also more humanlike. The bulge of Broca's area, essential for speech, is visible in one habilis brain cast, and indicates it was possibly capable of rudimentary speech. Habilis is thought to have been about 127 cm (5'0") tall, and about 45 kg (100 lb) in weight, although females may have been smaller.
Habilis has been a controversial species. Originally, some scientists did not accept its validity, believing that all habilis specimens should be assigned to either the australopithecines or Homo erectus. H. habilis is now fully accepted as a species, but it is widely thought that the 'habilis' specimens have too wide a range of variation for a single species, and that some of the specimens should be placed in one or more other species. One suggested species that is accepted by many scientists is Homo rudolfensis, which would contain fossils such as ER 1470.
Homo georgicus: in 2002 a fossils found in Dmanisi, Georgia, seemed intermediate between H. habilis and H. erectus. The fossils are about 1.8 million years old, consisting of three partial skulls and three lower jaws. The brain sizes of the skulls vary from 600 to 780 cc. The height, as estimated from a foot bone, would have been about 1.5 m (4'11"). A partial skeleton was also discovered in 2001 but no details are available on it yet. It is the first trace out of Africa.
H. erectus existed between 1.8 million and 300,000 years ago. Like habilis, the face has protruding jaws with large molars, no chin, thick brow ridges, and a long low skull, with a brain size varying between 750 and 1225 cc. Early erectus specimens average about 900 cc, while late ones have an average of about 1100 cc. The skeleton is more robust than those of modern humans, implying greater strength. Body proportions vary; the Turkana Boy is tall and slender (though still extraordinarily strong), like modern humans from the same area, while the few limb bones found of Peking Man indicate a shorter, sturdier build. Study of the Turkana Boy skeleton indicates that erectus may have been more efficient at walking than modern humans, whose skeletons have had to adapt to allow for the birth of larger-brained infants. Homo habilis and all the australopithecines are found only in Africa, but erectus was wide-ranging, and has been found in Africa, Asia, and Europe. There is evidence that erectus probably used fire, and their stone tools are more sophisticated than those of habilis.
Homo ergaster, some scientists classify some African erectus specimens as belonging to a separate species, Homo ergaster, which differs from the Asian H. erectus fossils in some details of the skull (e.g. the brow ridges differ in shape, and erectus would have a larger brain size). Under this scheme, H. ergaster would include fossils such as the Turkana boy and ER 3733.
Homo antecessor was named in 1977 from fossils found at the Spanish cave site of Atapuerca, dated to at least 780,000 years ago, making them the oldest confirmed European hominids. The mid-facial area of antecessor seems very modern, but other parts of the skull such as the teeth, forehead and browridges are much more primitive. Many scientists are doubtful about the validity of antecessor, partly because its definition is based on a juvenile specimen, and feel it may belong to another species
Homo sapiens (archaic) (also Homo heidelbergensis)
Archaic forms of Homo sapiens first appear about 500,000 years ago. The term covers a diverse group of skulls which have features of both Homo erectus and modern humans. The brain size is larger than erectus and smaller than most modern humans, averaging about 1200 cc, and the skull is more rounded than in erectus. The skeleton and teeth are usually less robust than erectus, but more robust than modern humans. Many still have large brow ridges and receding foreheads and chins. There is no clear dividing line between late erectus and archaic sapiens, and many fossils between 500,000 and 200,000 years ago are difficult to classify as one or the other.
Homo sapiens neanderthalensis (also Homo neanderthalensis)
Neandertal (or as I prefer Neanderthal) man existed between 230,000 and 30,000 years ago. The average brain size is slightly larger than that of modern humans, about 1450 cc, but this is probably correlated with their greater bulk. The brain case however is longer and lower than that of modern humans, with a marked bulge at the back of the skull. Like erectus, they had a protruding jaw and receding forehead. The chin was usually weak. The midfacial area also protrudes, a feature that is not found in erectus or sapiens and may be an adaptation to cold. There are other minor anatomical differences from modern humans, the most unusual being some peculiarities of the shoulder blade, and of the pubic bone in the pelvis. Neandertals mostly lived in cold climates, and their body proportions are similar to those of modern cold-adapted peoples: short and solid, with short limbs. Men averaged about 168 cm (5'6") in height. Their bones are thick and heavy, and show signs of powerful muscle attachments. Neanderthals would have been extraordinarily strong by modern standards, and their skeletons show that they endured brutally hard lives. A large number of tools and weapons have been found, more advanced than those of Homo erectus. Neanderthals were formidable hunters, and are the first people known to have buried their dead, with the oldest known burial site being about 100,000 years old. They are found throughout Europe and the Middle East. Western European Neanderthals usually have a more robust form, and are sometimes called "classic Neanderthals". Neanderthals found elsewhere tend to be less excessively robust.
Homo floresiensis was discovered on the Indonesian island of Flores in 2003 but doesn’t' fit in the evolutionary ladder. Fossils have been discovered from a number of individuals. The most complete fossil is of an adult female about 1 meter tall with a brain size of 417cc. Other fossils indicate that this was a normal size for floresiensis. It is thought that floresiensis is a dwarf form of Homo erectus - it is not uncommon for dwarf forms of large mammals to evolve on islands. H. floresiensis was fully bipedal, used stone tools and fire, and hunted dwarf elephants also found on the island. It could be that this group had a sort of Laron syndrome.
Homo sapiens sapiens (modern)
Modern forms of Homo sapiens first appear in the Pleistocene between 195,000 and 125,000 years ago. Modern humans have an average brain size of about 1350 cc. The forehead rises sharply, eyebrow ridges are very small or more usually absent, the chin is prominent, and the skeleton is very gracile. About 40,000 years ago, with the appearance of the Cro-Magnon culture, tool kits started becoming markedly more sophisticated, using a wider variety of raw materials such as bone and antler, and containing new implements for making clothing, engraving and sculpting. Fine artwork, in the form of decorated tools, beads, ivory carvings of humans and animals, clay figurines, musical instruments, and spectacular cave paintings appeared over the next 20,000 years.
Even within the last 100,000 years, the long-term trends towards smaller molars and decreased robustness can be discerned. The face, jaw and teeth of Mesolithic humans (about 10,000 years ago) are about 10% more robust than ours. Upper Paleolithic humans (about 30,000 years ago) are about 20 to 30% more robust than the modern condition in Europe and Asia. These are considered modern humans, although they are sometimes termed "primitive". Interestingly, some modern humans (aboriginal Australians) have tooth sizes more typical of archaic sapiens. The smallest tooth sizes are found in those areas where food-processing techniques have been used for the longest time. This is a probable example of natural selection which has occurred within the last 10,000 years.
It seems that the appearance and success of man gave a setback to the other type of apes: the various species of ape existing to day are, counted all together adding up to less than 200,000 individuals. It seems also that another big problem is not only the diminishing environment, as humans grew more and more but also a not too much efficient strategy in reproduction.
Independently from how much well Homo Sapiens Sapiens thrived in his origins the human population was reduced to a small number of breeding pairs - no more than 10,000, and possibly as few as 1,000 - resulting in a very small residual gene pool, according to the "Toba catastrophe theory", that assumes that of a massive volcanic eruption severely reduced the human population: this may have occurred around 70,000-75,000 years ago when the Toba caldera in Indonesia underwent an eruption of category 8 (or "mega-colossal") on the Volcanic Explosivity Index. This released energy equivalent to about 1 gigaton of TNT (4.2 EJ), fifty times greater than the 1980 eruption of Mount St. Helens, and twenty times greater than the largest man-made explosion, the October 30, 1961 detonation of the Soviet Union's "Tsar Bomb" a thermonuclear device. When Toba volcano in western Sumatra erupted 73,000 +/- 4000 years ago it was (and still is) the largest volcanic cataclysm to have taken place on planet earth for the last 28 million years.
According to this theory, the Toba explosion reduced the average global temperature by 5 degrees Celsius (9 degrees Fahrenheit) for several years and may have triggered an ice age. It's proposed that this massive environmental change created population bottlenecks in the species that existed at the time; this in turn accelerated differentiation of the isolated human populations, eventually leading to the extinction of all the other human species except for the two branches Neanderthals (H. neanderthalensis) already adapted to cold climates, in Eurasia and modern humans (H. sapiens) in Africa, where the impact of cooling was less hard. Eventually humans once again fanned out from Africa when the climate and other factors permitted.
They migrated first to Arabia and India and onwards to Indochina and Australia, and later to the Middle East and what would become the Fertile Crescent following the end of the Würm glaciation period (110,000-10,000 years ago).
The diffusion of man on the surface of the planet was a very long walk. Apart Antarctica and some little island all Earth was in the end populated, but it took a lot of time. The last group of hunter gathers arrived in the last place of human expansion when in other pat of the world empires had been established and had fallen. For clarity we give an account of the diffusion prior of relating about "civilization".
We made here a distinction between culture and civilization. Culture (from the Latin cultura stemming from colere, meaning "to cultivate") generally refers to patterns of human activity and the symbolic structures that give such activities significance and importance. Cultures can be "understood as systems of symbols and meanings that even their creators contest, that lack fixed boundaries, that are constantly in flux, and that interact and compete with one another". Culture can be defined as all the ways of life including arts, beliefs and institutions of a population that are passed down from generation to generation. Culture has been called "the way of life for an entire society." As such, it includes codes of manners, dress, language, religion, rituals, norms of behavior such as law and morality, and systems of belief as well as the art. In the opinion of the writer of this note every species that has a passing of behavior from a generations to another (also the mother cat teaching to catch mice at the kittens has a culture). All ancient species of humanoids an all the ancient groups of man had a culture.
A civilization or civilisation is a society or culture group normally defined as a complex society characterized by the practice of agriculture and settlement in cities. Compared with other cultures, members of a civilization are organized into a diverse division of labour and an intricate social hierarchy.
About 1,000,000 years ago walking a little space every generation humans arrived from Africa to China. Half million years after crossing the Caucasus they arrived in Europe. Other parts of the world required longer time: Australia was reached 40,000 ago, Papua 5,000 years after, during a glacial period that lowered the level of the sea. An area like Siberia required that mankind reached a cultural level enabling it to cope with cold climate 20 thousand years ago, from Siberia to North America took 8,000 years, and the crossing of the continent from Alaska to Terra del Fuego only a couple of millennia. The last areas to be occupied by primitive population were the Polynesian islands, Hawaii in the year 500 C.E. New Zealand 1000 C.E. and the last Chatham Island about
1350 C.E. Other places as the Mauritius Island was colonized later but civilized people did this and so is not to be thought as diffusion on man, but as colonization.
All in all about 10,000 years ago all the major part of the word had seen humans, Greenland included. It was a very diffuse but disperse presence. An informed guess sets the number of people that could live as hunter gatherers at about 5, 10 millions of individuals (to day Mumbay alone has 13,662,885 inhabitants). But about at that time something happened and the human story stopped to be natural history and became something different.
