Question

Why did graviattional collapse cause earth to heat up?

Answer 1

Actually, gravity still generates heat - because Earth is not solid. Heavier materials continue sinking down to a center, losing their potential energy in gravitational field. This movement generates heat.
Some scientists even hold a view that this is a major source of internal heat. But dominating view is that it constitutes only a minor part, while major part is done by radioactive decay.

This heat generation mechanism in no way violates law of conservation. The initial energy for this is a potential energy of gravitational field created by parts of a planet when they were still separate pieces. This energy is going down, while heat energy is going up (more exactly, it isn't, it is radiated away, becoming the energy of IR photons).

Answer 2

Actually, gravity still generates heat - because Earth is not solid. Heavier materials continue sinking down to a center, losing their potential energy in gravitational field. This movement generates heat.

Some scientists even hold a view that this is a major source of internal heat. But dominating view is that it constitutes only a minor part, while major part is done by radioactive decay.

This heat generation mechanism in no way violates law of conservation. The initial energy for this is a potential energy of gravitational field created by parts of a planet when they were still separate pieces. This energy is going down, while heat energy is going up (more exactly, it isn't, it is radiated away, becoming the energy of IR photons).