The ultimate source of energy for all life on Earth is the sun. Every form of life on Earth is dependent upon others, and without sunlight, most life on Earth would cease to exist rather quickly.
Although sunlight is the ultimate source of energy on Earth, not all life depends on it. Thirty years ago, it was discovered that openings in the ocean floor, miles below the surface called hydrothermal vents, were hot, despite the fact that no sunlight reached down that far. The bottom of the ocean has a constant temperature of near freezing, but these vents were receiving their heat from the Earth's core, not from the sun.
The hydrothermal vents have temperatures that range from 110 to 350 degrees Fahrenheit, and animals such as crabs, tubeworms and clams have thrived near the openings.
The sun takes care of all organisms living above the ocean floor by providing energy to plants that need it to produce food. Because animals cannot make their own food, they rely on plants to provide them with the energy to survive. Plants feed animals called herbivores, herbivores feed animals called carnivores and the decomposers feed on the waste left behind to begin the cycle again. This loop is commonly called the food chain. Without sunlight to help plants make food, most life could not exist for long.