Some archaea make their own food from sunlight, while others consume chemical compounds for energy. Archaea that create food from sunlight do not use the same photosynthetic process that plants and algae do and do not release oxygen as a waste product.
Archaea that produce energy by consuming sunlight are called phototrophs, while archaea that consume inorganic chemicals are called lithotrophs. The third group, the organotrophs, consumes organic compounds. No known species of archaea use traditional photosynthesis as it is used in plants and algae.
Lithotrophic archaea form an important part of plant ecosystems. These archaea fix nitrogen in the soil as a by-product of consuming and metabolizing ammonia for energy. Other lithotrophs, such as the anaerobic archaea that inhabit swamps, produce methane as a by-product. These archaea are the primary natural sources of methane.
Lithotrophic and organotrophic archaea can survive in environments that sustain no other form of life due to temperature, chemical composition or lack of sunlight. Their ability to metabolize chemicals such as ammonia, carbon dioxide and hydrogen sulfide means that they are not dependent on sunlight or the food chain. These organisms are found in oxygen-poor swamp waters, deep-sea vents, salt lakes, geothermal springs and other areas hostile to most species.