What is the main source of energy for Earth?

The Sun is the main source of energy for Earth. Its radiation supplies the light and heat that drive most natural processes at the planet’s surface, from photosynthesis and weather to the water cycle and ocean circulation.

Green plants capture sunlight through photosynthesis and convert it into chemical energy. That stored energy supports food webs, while ancient plant and microorganism remains became many of the fossil fuels used by humans. Solar heating also causes evaporation, helping power clouds, rain, rivers, and winds. Even wind and hydropower are therefore largely solar-driven systems.

Earth receives enormous amounts of solar radiation, although clouds, ice, land, and the atmosphere reflect or absorb different portions of it. The Moon is not an independent energy source because it mainly reflects sunlight. Water and wind are important energy resources, but they are usually intermediaries that receive much of their usable energy from the Sun. Geothermal energy and tidal energy are notable exceptions to this broad pattern.