What is the primary source of energy for almost all ecosystems?

The primary source of energy for almost all ecosystems is the sun. Solar energy drives the process of photosynthesis, where plants, algae, and some bacteria convert sunlight into chemical energy in the form of glucose. This fundamental process lays the foundation for most food webs, as it fuels the growth and metabolism of primary producers. These producers are then consumed by herbivores, which are in turn eaten by carnivores, creating a flow of energy through the ecosystem. Without this input of solar energy, the majority of life forms would be unable to survive, as the energy needed to sustain biological processes would be lacking.

The other options represent alternative energy sources that contribute to certain ecological processes but do not serve as the primary energy drivers in the majority of ecosystems.