Extremophiles

Extremophiles — organisms that thrive in conditions lethal to most life — have redefined what is possible for biology and transformed our understanding of where life might exist in the universe. They live in environments once thought uninhabitable: hydrothermal vents (400°C water, crushing pressure); Antarctic ice (−20°C, no liquid water); highly acidic hot springs (pH <2, equivalent to stomach acid, boiling); hypersaline lakes (10x saltier than ocean); deep subsurface rock (3km underground, 3.5 billion years without sunlight); and radioactive environments (Chernobyl, Deinococcus radiodurans withstands 1.5 million rads — 3,000x the lethal dose for humans). Tardigrades (water bears, 0.5mm) are the most famous extremophiles: they survive all of these conditions plus the vacuum of space and cosmic radiation — they can enter cryptobiosis (suspended animation with 3% water content) for decades and revive when conditions improve. They have been brought to space on the Russian FOTON-M3 satellite (2007) and survived. Deep subsurface microbes living on hydrogen produced by rock-water reactions may represent the most ancient form of life and could account for the majority of Earth's biomass. Extremophile research drives astrobiology — if life can thrive on Earth in these conditions, it may thrive on Mars, Europa, or Enceladus.