Life – not as we know it

Life in other places in the universe may be farther or differently evolved such that we do not recognize it. Studying extremophiles on Earth suggests that this could be the most likely form of life uncovered on other planets and moons such as Jupiter's Europa and Callisto and Saturn's Enceladus.

Extremophiles are organisms which thrive in extremely hot or cold temperatures such as deep sea vents and cracks 50-100 km below the Earth’s crust in the mantle. Extremophiles consume and metabolize gas expelled from deep within the Earth, suggesting that the sun or proximity to a sun is not an exclusive pre-condition for life. The total weight of extremophiles is thought to equal that of all of the species of animals living on the surface of the Earth.

Whether archaea extremophiles can evolve into specialized multi-cellular organisms and evolve intelligence is a separate question and perhaps thought to be unlikely. Although some scientists like Thomas Gold in "The Deep Hot Biosphere: The Myth of Fossil Fuels" speculate that the origins of life may be via extremophiles rather than from ponds or amino acid-laden meteorites.