Why hasn't earth's crust become as hot as the Mantle even after so many years? Is it such an insulater?

Question

If the earth is more than 4 bn years old, and its Mantle is at 1000 deg C, then shouldn't we expect the earth -crust (40 km thin) to become equally hot due to conduction of heat (after such a long period of time)? Or is the material of the crust such a bad conductor of heat? If so, then really how bad conductor is it?

Answer 1

The temperature of the crust increases with depth, reaching values typically in the range from about 500 °C (900 °F) to 1,000 °C (1,800 °F) at the boundary with the underlying mantle. The crust is brittle and rigid because of the effects of the cold universe on the outer edges of the earth. The brittleness of the crust is not related to its ability to conduct heat, it is just being heated from the interior by the core, and cooled from the exterior by the cold universe! :)

Hope this helps!

Answer 2

You have given the two answers in your question.
The crust is too thick, and it is composed of extremely poor conductive matterial.
However, in some spots on Earth the crust is thinner and the heat from magma underground can be easily felt. 40 km might seem thin to you but that is almost 25 miles thick. If you had a mountain that was 25 miles thick and you applied a heat source on one side, you wouldn't expect the other side to heat up.

Answer 3

Because the Earth is actually cooling down. Billions of years from now, the Earth will eventually cool all the way down and be one solid rock and all activity on Earth will stop.

Think wax, you warm it up and it melts, but after it sits for a while, it eventually cools down and forms a hard layer on the outside. even though the inside is still hot, it doesn't melt the wax outer layer. Instead, it continues to cool.

This is because of the transfer of heat (heat transfer) - heat goes from hot to cold, so the heat from our Earth is escaping into space and we are slowing cooling down.

Answer 4

Rock is a horrible conductor of heat.