Dot Physics: What are the Sources of the Energy Sources

The main sources all trace back to the sun (which has a surface temperature near 6000 ºC)

The interior of the Earth is warm mostly due to gravitational potential energy. Basically, the stuff that formed the Earth was gravitationally attracted and kind of “fell” together. When they collided, they got warmer. There are other contributing factors to the interior temperature of the Earth, but I think this is the biggest one.

Rhett glosses over something here (and admits it in the comment section); radioactive decay is an important process in heating the interior. Early determinations of the age of the earth include a calculation from Lord Kelvin, who assumed cooling of a molten mass and came up with an age of several tens of millions years. Much older than the creationists/Biblical literalists, but not young enough according to the newly minted theory of evolution. Kelvin was unaware of radioactive decay, which keeps the interior warm.

I have one other nit with an otherwise fine post

[W]hy does burning fossil fuels give you energy? How about I say that in the burning process, chemical bonds are broken in such a way that you get energy.

This is a pet peeve of mine. Energy is released in forming bonds. Burning fuels give you energy because you break the existing bonds and form stronger ones.