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

Given that the Earth's 'plates' are constantly moving, and that the Himalayas marks the meeting point of two such plates, are the Himalayas getting taller? Some scientific input is demanded here I feel.

Yes.

Well, thanks for that - very erudite. Will certainly stop the sleepless nights.

What I've always found most interesting about mountain ranges is that the highest peaks are actually from the syncline (ie. the bottom of the warp in the rock) as the rock here is very compressed and hard to erode whereas the rock at the anticline (the top) disappears very quickly as it is stretched and brittle.

So the stuff at the bottom becomes the top.

(am I mixing up my synclines and anticlines? )

I saw a fascinating report on this on ABC TV (Australia) just this week

there's a transcript at http://www.abc.net.au/catalyst/stories/s1360803.htm

ties in all the recent quakes etc

India is moving northward with respect to Asia at a rate of about 2.4 inches per year. This pushes up the Himalayas, and the Tibetan Plateau, which then spreads out northward like a giant lump of silly putty in a series of "north south extensional basins".

I don't know the exact amount the mountains are growing each year, but I've seen a figure of 5mm quoted.

I logged on to Mike Sandiford's site and tiptoed tentatively through a section of the amazing landform map. Bit lost for words now. Thanks for the 'Fractured Future' info, it will remain a priority.

It was a great report! A friend said that he found it a little "worrying" but let's face it - there's not much we can do about it - so why worry

I'm pleased that you found it as interesting as I did

There are more mini quakes going on than most people realise, but there is just so much daily 'racket' in our lives that we don't hear them or feel them. I don't believe we are listening enough to the earth, but as you say, there is little we could do about it anyway. But it might put us in our place to listen. We haven't quite reached 'stop the world I want to get off' stage. (or have we?)

In the Asian Tsunami Disaster, did a chunk of seabed displace upwards or displace downards in the 'quake? In an upwards displacement is a hollow space left underneath? and similarly if the displacement was downwards, does that mean there was a hollow space for it to drop down into? I sometimes think of how the world would look if we took all the seas and oceans off and all I can imagine is that it must be like a very well bitten apple with just a big chunk of the original rounded shape still evident on the top half and loads of bitten away stuff on the bottom but leaving the Sout Pole so to speak. As all the other planets look nice and round why are we, without the seas, so bitten and ugly?

From space, the Earth looks perfectly smooth. A kilometre or ten isn't noticeable compared with the size of the planet.

I *think*, if I remember rightly, a chunk of seabed displaced upwards (by 20 metres I think...) to cause the tsunami wave in December.

Regarding other planets being "nice and round"... that's certainly not true of Mars, for example. The average height in one hemisphere is much larger than the other. Mars also has a volcano (Olympus Mons) that's a lot larger than any of Earth's mountains (three times larger than Everest according to A330683). Mars is probably more "rounded" than Earth, but that's because we have plate tectonics on the Earth, whereas on Mars plate tectonics appears to have happened in the past but is not happening at the moment.

I would also be surprised if Mercury, Venus and Pluto were "nice and round".

Having said all of that, if you scaled all the planets down to the size of a football, say, the mountains and trenches on Earth would be hardly noticeable - Everest, for example, is under 10km above sea level and the radius of the earth is nearly 6400km.

The gas giants are a different matter entirely; just because of their different composition I would expect them to be more spherical. They will have slight equatorial bulges due to how they orbit the sun.

Nice to see some geological discussion in ask

The equatorial bulge in the gas giants is because they are spinning on their axis, not because of the way in which they orbit the sun.

But are the great seas and oceans there simply because there are huge 'hollows' to put them in? If water hadn't 'evolved' then wouldn't earth resemble a bitten up apple? Could we have evolved with less water than we have or was the quantity pre-set by other factors? If so, what contributed to those pre-setting factors which enabled us to end up with the quantity we now have? So many questions to ask and so little time...

Good question. I've seen lots of diagrams of the breakup of the single supercontinent Pangaea, and I've even seen some speculative ones of where the continents were before they joined to form Pangaea, but I've never seen any explanation as to why the surface is divided into oceanic plate and continental plate. They're quite different from each other.

What a fascinating discussion this has become

I've heard speculation that the giant continental landmasses are remnants of giant shield volcano activity from earth's formative years.

The canaries and the hawaiian islands are shield volcanoes and manage to make substantial land mass, imagine that scaled up as earth cooled and that is where the basal rock came from.
only a theory but certainly a possibility.

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Anyone know this for sure? I've read that continental landmasses are lighter than the seabeds, and that's why they haven't sunk in the last few billion years.

Moving rivers, the great oceans are around 2-3 km deep (roughly - not including the subduction zone trenches). Compare that with the 6000ish km diameter of the earth and you will see that if you removed the water from the ocean basins the earth from afar would resemble an apple with pathces of skin peeled away rather than a bitten apple.

Water didn't evolve it is simply one of the molecules extant from the formation of the planets. It was simply just there. Things float on other things according to their densities. Iron is densest of the earth's main constituents and so forms the core. Liquid rock floats around it (the mantle) and solid rock - less dense again, floats on this. Water is then less dense and because of gravity it occupies the position it can closest to the centre of gravity. Hence the oceans. The constituent gases then form the atmosphere, at least those that are dense enough to be trapped by the gravitational field (unlike Helium and Hydrogen).

What caused the relative quantities of iron, rock, water, oxygen, nitrogen etc. is purely in the realms of theory. The overall distributions of the elements though are preset by the conditions that cause them to be formed. Hydrogen and deuterium (heavy hydrogen) only were formed in the big bang. Higher elements up to carbon (ish) are formed from nuclear fusion in stars. All other elements need a supernova explosion to be formed.

From the overall distribution of elements one can speculate about which compounds will be formed in interstellar space and in the accretion discs of newly forming solar systems but it's a tricky tricky problem.

Yes continental rock is lighter than the ocean floor rock. No, nobody knows for sure how the continents were formed. What I just said was one theory. I'm unaware of other theories for their formation.

So what can I read which will give me basic information and then advance in user-friendly chunks without being overwhelming in the initial stages and deadening interest? Some useful guidelines for this would be appreciated, if you don't mind taking this task on board. It's a fact of life that we are surrounded by so much information both visual and audial on so many things that we have a presumption that we 'know it all'. But then you find you know nothing at all, just an acceptance of existence and all it might contain which is certainly uncontainable for one person. However, I would like to contain some of THIS bit if you could point me in a beginner's direction.