The core of Earth?

Question

If the core of the Earth is far away from the sun then how is it so hot?

Answer 1

"There are three main sources of heat in the deep earth: (1) heat from when the planet formed and accreted, which has not yet been lost; (2) frictional heating, caused by denser core material sinking to the center of the planet; and (3) heat from the decay of radioactive elements.

It takes a rather long time for heat to move out of the earth. This occurs through both "convective" transport of heat within the earth's liquid outer core and solid mantle and slower "conductive" transport of heat through nonconvecting boundary layers, such as the earth's plates at the surface. As a result, much of the planet's primordial heat, from when the earth first accreted and developed its core, has been retained.

The amount of heat that can arise through simple accretionary processes, bringing small bodies together to form the proto-earth, is large: on the order of 10,000 kelvins (about 18,000 degrees Farhenheit).

Additionally, descent of the dense iron-rich material that makes up the core of the planet to the center would produce heating on the order of 2,000 kelvins (about 3,000 degrees F). The magnitude of the third main source of heat--radioactive heating--is uncertain. The precise abundances of radioactive elements (primarily potassium, uranium and thorium) are is poorly known in the deep earth.


In sum, there was no shortage of heat in the early earth, and the planet's inability to cool off quickly results in the continued high temperatures of the Earth's interior. In effect, not only do the earth's plates act as a blanket on the interior, but not even convective heat transport in the solid mantle provides a particularly efficient mechanism for heat loss. The planet does lose some heat through the processes that drive plate tectonics, especially at mid-ocean ridges ."

Answer 2

to rephrase gentleman's answer:
1. compression - heated the earth when it was being formed
2. friction - as dense liquids were pulled into the center
3. radioactive decay

Answer 3

Nuclear fission