What is the primary source of energy for most ecosystems on Earth?

The primary source of energy for most ecosystems on Earth is the Sun. This is because solar energy drives the photosynthesis process, allowing plants to convert sunlight into chemical energy. Through photosynthesis, plants produce oxygen and organic matter, which serve as the foundation for food chains.

Photosynthetic organisms, such as plants, algae, and some bacteria, form the base of the ecosystem, supporting various heterotrophic organisms (herbivores, carnivores, and decomposers) that depend on them for energy. This reliance on sunlight means that the distribution and productivity of ecosystems are largely influenced by the amount of solar energy they receive.

Other options such as moonlight, wind energy, and geothermal heat do not play a predominant role in supporting the main energy processes for ecosystems in the same way that solar energy does.