As humans we have two main heat energy sources: the sun, and the earth. Unfortunately, the earth's heat can't support life on its own, so we are pretty much totally dependent on the Sun. (which will go out in a really long time). Pretty scary, huh?( I am glad that I wont be alive then)!

 The Sun produces heat and light and sends it to earth in the form of radiation. That thermal energy goes into plants, which use it, and light, and carbon dioxide to make carbon stores/sugar stores. They take CO2 and change it into carbon. Then the herbavor eats the plant and takes the carbon stores and adds them to itself. Then along come some people and eat the herbavor to get those carbon stores into ourselves.

This is energy transformations.