Well basically, the Sun is pretty much our energy source. Without the Sun alot of the living organisms that roam here on Earth would probably perish, that is including humans. Without the Sun, there would still be science, just alot of it narrowed down to few pieces of information. The Sun is what provides any heat at all, or any oxygen. Or alot of things here on Earth. So the answer is true, the Sun is the heat source for convection currents anywhere. :)