Why is there plate tectonics on only one terrestrial planet, Earth? Shouldn't Venus, being almost the same size, have also formed active plate tectonics? :-k

Venus is thought to renew its crust and shed internal heat (which is what plate tectonics does for earth) in a different way. Most of the time, its crust is stable and motionless. However, over the course of hundreds of millions of years, heat builds up in the planet. This heat is then released all at once, melting and renewing the entire Venusian surface . That explains why there are no really old craters on Venus.

Also, I think water has a role in plate tectonics on earth.

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Does water act as a lubricant between the plates?

I don't think so. Water is more than just a liquid. It is also a chemical component of many rocks and it changes their structural properties. Specifically, rocks on Venus are much stronger than their counterparts on Earth.

I'm reaching back years in my memory for this info. I may not be right. :-?

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It might. No one knows for sure, but that has been proposed.

It may also be that the Earth's crust was the right composition for plate tectonics only after the Mar's size impactor formed our Moon. I have seen that proposed as well.

The problem is that Earth is the only planet we know of that has ongoing plate tectonics, and it is hard to be certain of much when your sample size is = 1.

That's an explanation of what happens to an earth sized planet if there is no tectonic plate movement to facilitate heat release. Doesn't explain why there's no tectonic plate movement.....

Could the Moon play a role I wonder?

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Andy

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There are rift valleys on other worlds (Valles Marineris on Mars for example) that could have been the start of plate tectonics if there had been enough heat to keep the process going. I don't think a giant impactor is needed.

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Or nine.

I thought I read that Europa might have plate tectonics of a sort. Of course water would play a cruicial role in Europan tectonics since the materials are water ice sheets floating above a mantle of liquid water.

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J Pax

Pretty logical. The idea is that most of the crust was blasted away which formed the Moon. This thinner crust allows for much more dynamics like land above water for one. More here

[Edit. The "thinner" idea may, or may not, be a good one as it is just something that comes to mind. Ocean basins created appears to be the main benefit as water had a place to go so land would emerge.]

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Hard to say. If Mars' crust had been thinner, or if it had deep oceans, then maybe it would have had plate tectonics even if they turned out to be short lived because of the loss of heat.

But only 1 with tectonics. So it is hard to say just which features are crucial for it to happen.

That was a good link, George. Quick follow up question. Does anyone know how much & the crust is compared to the entire Earth?

Thickness of the Earth's crust:

http://quake.wr.usgs.gov/research/st...stalStructure/

Well, you need the others to tell you which ones aren't. Which is why I say the sample size is nine--even more if you count the larger moons.

I think another thing to remember is the fact that Venus has no magnetic field but the Earth does. This fact implies that Venus's core is not as dynamic as the Earth's, which may be the reason there are no tectonics on Venus.

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