[Moltke]

Wouldn’t earth 4 billion years ago have been quite a bit warmer on the inside? Like a pie fresh out of the oven? That would have made the crust warmer as well.

[muawiyah]

The answer is that the residual heat from gravitational collapse would have dissipated quite quickly ~ couple of hundred million years in fact ~ or even faster.

What keeps Earth's interior warm is radioactive decay ~ the current proposal is that thorium is the main source, but there are other possibilities ~ maybe even a natural uranium reactor at the central part of the core!

[cripplecreek]

Not to mention the fact that there was far more volcanism going on at the time.

[onedoug]

But how did God bring that about?

It’s possible that iron was in heavier abundances during early solar system history (especially in its inner parts) and that it formed Earth’s, and other terrestrial planetary cores early on. That, with radiogenics also settling out, may have provided enough heat for this not only on Earth, but also on Mars which seems to have had an abundance of early water on its surface as well.