Why is the ultimate source of most energy in the earth
The huge ball of nuclear fusion in space that the earth orbits.
The Sun is the source of energy for Earth. It gives life to plants which convert sunlight to energy, and plants give energy to animals, etc.
the core of the earth.
If we could harness the energy of the ocean waves, that would be a never ending source of power.
Liquid iron core. On the surface is the sun.