[Petrochemicals (OP)]

On the " quuestion of the week" thread about the effects of the early earth impacts and absorption of other bodies tectonic plates where mentioned as an effect of planitary collision. It is stated that earth having tectonic plates is to do with granite, which floats and seperatley Earth having liquid water.

Any more to add?

[paul cotter]

A simplistic answer: the interior is at a high temperature and molten and the outer layer has solidified due radiation lowering the temperature. Cracks in this solid outer layer allow separation and movement.

[Petrochemicals (OP)]

I was looking for a bit more depth Paul, for example why does Venus not have tectonic plates.

[paul cotter]

Venus?, hmm, I never visited there so I don't know, I believe it's a bit hot. I gave you a simplistic answer as no one else had replied and it's all I have, maybe some one more knowledgeable can contribute?

[Petrochemicals (OP)]

I dod leave it up a while before replying, but i guess there are not many expert geologists where as physicists seem ten a penny. It is a bit quiet even though of late, even to the point of a lack of relativity questions.

[paul cotter]

Yep, it has been very quiet lately, disappointing. Since I already know everything, I have no questions left!(joke, of course).

[diverjohn]

I suspect the earth has a more dynamic composition than does Venus because of the widely held idea that a large body crashed into the early earth and that kinetic energy threw off enough material to coalesce into our moon. The combination of heat from the impact and the gravity of the moon pulling on the crust give our world the moving crustal plates.

[evan_au]

To add to the comment by Diverjohn...
During the expected glancing blow between Thea and Earth, it was mostly lighter crustal material that was thrown out to make the Moon.
- This meant that the floating crustal material no longer covered the whole Earth in a solid thick skin
- So the remaining crustal material was thin enough to be pushed around by convection currents in the mantle beneath, forming continents where convection cells converged, and splitting them apart where convection cells diverged.

Perhaps the lack of a large, low-density moon may explain why neither Mars nor Venus have plate tectonics?

https://en.wikipedia.org/wiki/Origin_of_the_Moon