Archaea are single-celled microorganisms that are distinct from bacteria and eukaryotes and form the third domain of life. They are often extremophiles, flourishing in extreme heat and cold, and can be found inside volcanos and undersea vents on the ocean floor. It is hypothesised that they may live within the hot cauldron that is the magma of inner Earth where they may or may not produce oil in Earth's deep hot biosphere. 

Some archaea can survive for thousands and possibly millions of years entombed within crystals of salt. They are key players in biotechnology and life-extension tech.