Transcript: We tend to think of the evolution of life in terms of a sequence from simple organisms to large and complex organisms, but we should remember that even now, most life on Earth looks nothing like us. There are many more prokaryotic species, involving cells without nuclei, then eukaryotic species. There are many more species that can survive physical conditions that would kill us then there are large and complex organisms like us. Collectively, these species are called extremophiles. They like and thrive on extreme physical conditions. They are drawn from two of the three main branches of the tree of life, bacteria and archaea. Extreme life forms are common on this planet, and extreme conditions have been common in the history of this planet so naming them extremophiles is just a matter of definition.