What is the ultimate source of energy in an ecosystem?

The sun is the ultimate source of energy for nearly all ecosystems on Earth. Through the process of photosynthesis, plants and other autotrophs convert solar energy into chemical energy stored in organic compounds like glucose. This energy then flows through the ecosystem as herbivores consume plants, carnivores eat herbivores, and decomposers break down dead organic matter. Solar energy drives not only biological processes but also weather patterns, ocean currents, and the water cycle. While some deep-sea ecosystems rely on chemosynthesis using geothermal energy, the vast majority of Earth's life depends directly or indirectly on sunlight as their energy foundation.