Lately I have been thinking about where the energy on the earth ultimately comes from. For the most part I can only come up with three sources.
The first category is incident on the earth, this includes things like solar and cosmic radiation. In this category we have things like wood, alcohol and other fuels or things like wind energy, which are really just storage methods for solar energy.
The second category is energy that is trapped in the earth from its formation, this includes things like radiation, and other elemental chemicals and substances that can be used to react and give off energy.
The third source is gravitational, which comes to us as tides, and additional heating of the earth's core.
I am wondering if I have missed anything here, or if these are our available sources of energy on earth.
Depending on how far you go with your thinking, you may even be able to further reduce these sources to just two or possibly one source being gravitational. As one could make the argument that the sun and stars are just gasses which were trapped by gravity. I don't really want to go that far because I want to focus on the energy available to us on the earth as opposed to how it got there, but you're welcome to have at it.
I find that by thinking that most of what we consider fuel like gasoline is really just an indirect storage method for one these sources is different than what I am used to.
I am looking for additional insight and energy sources I missed, so have at it, as I am interested in what everyone else thinks.