h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

How did life get started? We keep hearing about how there must be billions of planets that could support life and any planet capable of supporting life must, inevitably, give rise to life. If life is as easy and inevitable as many people - even scientists - seem to think, why can't they get it started in a laboratory. They can get an assortment of amino acids to form and put that forward as evidence that it's easy. Life is much much more complicated than a jumbled collection of amino acids though. Anybody here care to speculate ...

Hello,

Actually, some would argue that life isn't that much more complex than a bunch of amino acids, since those form proteins and proteins are the building blocks of just about anything alive. Sure, they haven't worked out some of the higher processes to go from that to a basic cellular organism, but it's a great start.

Yours,
Jake

Ah Sal, a question that I've always found interesting and one day I intend to write an article on it for h2g2. Much research has been done but it is difficult to get funding for such clearly blue-sky research in at least the UK these days.

First off, Fred Hoyle's idea that it came from comets is not any sort of argument at all really, it merely shifts the problem from how did it start on earth to how did it start somewhere else...

The experiment you mention is one where you simulate what we postulate as the primeval atmosphere in a tank and then zap elctricity through it - simulating lightning. The primeval atmospehere contains plenty of water, sulphur dioxide, ammonia, methane, carbon dioxide and phosphorus - containing the main elments that make up organic molecules. This experiment has its successes, ie. you get many of the essential amino acids in the mixture and also sugars and cyanide - the purine and pyrimidine bases that occur in DNA and RNA are essentially condensed cyanide molecules. The problems are that not *all* of the essential amino acids are there, just most of them and in the sugar mixtures the quantity of ribose - the sugar in DNA and RNA nucleotides is esssentially missing - ie. it makes the wrong ones. This is however, a pretty basic experiment and it could be a reasonable simulation of what was merely the starting point. The other problem is that DNA, RNA and proteins are highly sensitive molecules, in the lab you have to generally handle them ice cold or colder in order to avoide them denaturing. The exceptions to this are the ones you tend to find in the archaebacteria found in hydrothermal vents at the bottom of the ocean (black smokers) - the DNA polymerase from one of these is the basis of PCR, the technique behind cloning). The conditions used in this experiment will in no way allow the formation of the unstable complex molecules that now make up life.

It has been postulated that the orignal polymers of life (RNA, DNA, proteins) may have formed on repeating surfaces (rock crystals) where they may have had a modicum of protection from the harsh atmospheric conditions and also the repeating crystal lattices may have formed an early base for copying of molecules in to daughter copies. Possibly, but will we ever know for sure?

The problem of the origin of life is a chicken and egg question. DNA encodes for proteins which are the molecules that actually perform the chemistry that build the DNA copies - but of course no protein can really be made that will do the correct task unless it is assembled from a safe, repeatable code suh as that on DNA strands.
So how did nucleic acids first replicate if there were no proteins to make copies and/or how did proteins assemble nucleic acids without a code for themselves to be assemled in the right structure and sequence? DNA itself cannot perform reactions whereas proteins have no innate code for replication.
The answer is possibly RNA. There are now known to be so called catalytic RNA molecules (so-called ribozymes) which have a nucleic acid code but also are able to perform simple chemical reactions - these are usually located on ribosomes the structures in cells that make new proteins. The trouble is if this is true, the original self replicating RNA disappeared from our ecosystem long long ago leaving few clues as to whether or not it really existed. Stablilty is also a problem. The reason DNA rather than RNA is used as the code for life is that DNA is considerably more stable to breakdown than RNA - the 2-deoxyribose in DNA has an OH (alcohol) group missing when compared with RNA and this simple difference means that DNA is much more stable to hydrolysis under ambient aqueous condiions that RNA is - RNA would be a poor template for replication as it will degrade too easily and hence the fidelity of replication that is possible with DNA in not possible with RNA. This of course does not mean it did not happen.

The other molecules that are missing from the 'primeval soup + lighning' Experiment are lipids. These are the fatty molecules that form cell membranes. How could these replications occur without a protective membrane to stop fast degradation of them. One plus oint is that when long fatty acids are put in water they do spontaneously form liposomes which are a double membrane of fatty acids (exactly like our own cell membranes) with a space in side in which can reside any number of entities.

Even were one able to explain how such molecules were originally formed it still takes an enormous leap to get to a fully functioning cell. Even the simplest cells of archaebacteria and bacteria have a complex structure containing organelles such as ribosomes and a myriad of proteins plus complex machinery to switch on and off the various genes in the genomal DNA that only should be expressed when appropriate.

A fascinating question, and one that has led me to ramble on quite spectacularly. Thankyou Sal for allowing to vent off on such a intersting topic .

Of course, one reason the lab experiments have not yet "worked" is that they haven't been going on for a few million years.

Quite, but would they ever when they don't produce ribose at all? Tricky to form nucleic acids without it. Also, a nice spare planet to conduct a real simulation would be nice too

Also, they were merely designed to test whether the building blocks of life (amino acids, purines, pyrimidines, sugars and lipids) can be produce from a primeval atmosphere and really they do show that that can happen quite well - with certain exceptions (and that may merely show a flaw in the experiment that a flaw in the postualtion).

They never created life in the laboratory, that´s true. But if you want to show how a house was created, showing how the bricks were created is a good start.

Exactamundo Xanatic. Unfortunately, we can never look back directly at what really happened and so we must postulate what happened and design experiments that show that the postulate is possible. In as similar way, physicists can never go and actually look at the big bang so they must pose a question and their huge supercolliders can either support the question or refute it, in which case the theory can be improved upon. When you have a good simple model that works to a reasonably consistent degree then you can start increasing the complexity of the model and see if you can simulate more difficult problems.

Good old Orcus! What a great answer! Now I'm going to be waiting for that article - drumming my fingers and tapping my toe.

The requirements for starting life are much MUCH more complex than a bunch of amino acids, aren't they? It may be a very good start - just as a pile of bricks may be a good start if you mean to build a house. But the chances of just the right amino acids coming together in just the right sequences to do anything that might resemble life is considerably less likely than the house building itself out of the pile of bricks you have ready for the job.

If it weren't for the fact that we're all here to prove it IS possible, it would be tempting to conclude that life was impossible

Before anyone can answer the question of how life got started, someone's got to answer the question: What the heck IS this life stuff anyway? Philosophists and scientists can't even agree on a concise definition to go by.

But it is fascinating that a living organism can be so catagorically different from "normal" matter, yet be completely made out of said stuff. I guess it's basically an organizational kinda thing. You get enough of the right kind of matter together, and it naturally falls into a certain grouping. And given a big enough universe, the chances are pretty good that at some point it's gonna happen.

What's even more fascinating than HOW life got started, though, is WHY life is even possible. Why is the universe made out of stuff that naturally organizes itself into structures which, apparently, have free will, and the ability to actively affect other matter. It's just plain weird, in my opinion.

One problem with thinking about 'the odds' of life developing is not just that multimillion year spans of time are hard to comprehend.

You can imagine a chemist randomly playing with a few test tubes of primitive chemicals and maybe then imagine that experimentation going on for a few thousand, or even a few million generations.

However, when you come to think of how many test tubes you'd need to model even a square mile of primordial Earth, and then how many square miles of potential reaction area might have been involved, it becomes apparent that not only is there an immense time-span, but also an unimaginably large area for reactions to occur on.

Indeed it is pretty freaky if you really think about it.

Can't remember what it was now but I saw a TV programme a couple of years ago demonstrating just how amazing a thing it is that we've got life here at all. Not only are we just the exact distance from the earth for ambient temperatures, we live on a planet that is just the right size so that water exists in all three states of matter (solid-liquid-gas) and that it can hold onto a good atmosphere. In addition to this, and even more lucky is the presence of the Moon. The orbital axis of the earth precesses around like a gyroscope. The moon stabilises this precession, meaning that the earth always tilts at roughly the same angle towards the sun, leading to our nice stable climate. If the moon were not there then the orbital axis could flip around all over the place and this would be disastrous to climate. Imagine the earth suddenly spinning with a polar ice cap directed exactly towards the sun. The ice cap would rapidly melt and one hemisphere of the earth would be perpetually in daytime and the other in darkness. Imagine the sort of cataclysmic effect that would have on climate and life as we know it... It would be doubtful that anything higher than bacteria and viruses would survive or would ever have developed as this would be extrememly destructive to higher forms of life.

It is incredible how robust our ecosystem is -having survived major events such as asteroids colliding with the earth yet how amazingly fragile it is also in an exceptionally hostile universe.

Large movements of the axis of rotation would certainly make climate horrendously unstable, but to get one hemisphere permanently lit, I think you'd need a vertical axis, with the earth rotationally locked to a one day per year timing (like the case with the Moon-Earth system) - a horizontal axis would end up with each pole having 24-hour sun in its summer, and 24-hour darkness in the winter, and the equator having two cycles per year moving from 24-hour twilight through 12-hour days and back to twilight.

er, yeah, that's what I meant. I think this occurs with the other planets does it not (I seem to recall either Uranus or Neptune has its rotational axis pointed directly at the sun).

I first have to admit I have never been a big fan of evolution. But then recently I read a book, that has made me loose pretty much what confidence I had in it. But since I haven´t got any better ideas, for this discussion I will go on with evolution.

It is very unlikely that a house can assemble itself that´s true. That is an argument often put forward by creationists. But you forget that evolution isn´t a random process. Imagine a slot machine. You could spend a long time in Vegas trying to get jackpot if you just pulled the stick all the time. But luckily they have these hold functions. If you happen to get an orange or a crown, whichever is good, you hold it and then continue with that. The same with evolution. Whenever something is created that works, it has an advantage and will multiply. And then those many copies will again start to mutate, but will be different and probably more complex than the previous. I know I´m not good at explaining this, but look up a book on evolution instead.

Which book was it that you read that made you question evolution?

Hello,

Well, there's always people who would present you with the Anthropic Principle, which states that our being here to observe it means that things pretty much worked out the right way (or in other words, looking back in time and calculating the odds are pretty silly). It's possible there are many other worlds where things didn't work out, but we don't have them as a reference for what the odds really are.

In a similar vein, imagine you flip a coin 10 times and get heads the entire time. This may seem like it's extremely rare, but it's got the same probability as any other sequence of 10 flips. Or try to calculate the odds against you being born. Yes, it worked out that way, but it probably doesn't mean there was some divine purpose guiding your eventual birth (unless you're of the megalomanical persuasion).

Yours,
Jake

Yes, but we're not talking about how we got to where we are now, Xanatic. The question is *How did life GET STARTED*? Compared to that question, evolution seems like a doddle, don't you think?

Another helpful thing to life on earth, according to the speculations of some scientists, is the presence of Jupiter that sucks large and lethal asteroids into itself, thereby protecting earth from collisions that would repeatedly wipe us out before life could ever get evolve.

Well, what I described also goes for life. Life is a self-replicating process. A long time ago a lot of chemicals components mixed together. They all fell apart again. Untill one wonderful day when one arrived that could reproduce. And therefore had an advantage compared to the others.

The book was by Gary E. Parker. I think it was a collection of essays really, so it doesn´t have a title in English. I´ve read a lot of Creationist stuff, but this was the first guy that didn´t sound like he had flunked high-school biology. And he also managed to go through the whole book without a "If evolution is wrong the Bible must be right" attitude.

In case it isn't clear, I'm not a creationist. I'm ever so very interested in how life began and not in the least bit interested in resorting to supernatural explanations. That would be no better than the example given by Orcus of Fred Hoyle's idea that the first life was carried here on comets. If you assume, for whatever reason, that life on earth was started by some entity, then the focus shifts to how the life of the entity was started. The assumption answers nothing.

The way you describe what you imagine happened: "one wonderful day" and "had an advantage compared to other", makes it sound as though life was *trying* to happen - there was a struggle to replicate and replication was "wonderful". Could that be so? Does that seem possible?

I'd imagined that how ever it had happened, it was pure, one in an almost infinite number of zillions chance. Have a careful read of Orcus' post number 3. It's not enough for just any old bunch of amino acids to be slung together, to make a protein. They have to be stitched together in a specific order and if they should, by some haphazard, astonishing chance, manage to just fall into the right order, how do they then replicate? It really is fascinating

I have no trouble with evolution by natural selection once you have something which can be called an organism - creationism is a circular argument if it's anything - but the beginning of life is much more problematic.

How can one molecule be selected for as opposed to another? What environmental conditions will result in the proliferation of particular amino acids, or the production of longer chains thereof?

I don't believe in an active god who intended to start life off using this tortuous route (Genesis is more believable than that!). I can't see what benefit a molecule could enjoy that would make it more likely to recur.

Maybe things just started by habit, like crystals - blobs of primeval slime accreting on rocks in the primeval soup, providing new micro-environments in which new formations could be generated.

Maybe old Rupert Sheldrake is right - when something has happened once it becomes more likely to happen again. But is morphic resonance really more believable than creation?