Bacteria are ubiquitous on Earth, and live everywhere
eukaryotes do. Many of the other more extreme environments
in which bacteria are found would be lethal to any
other form of life. Bacteria live in hot springs that would
cook other organisms, hypersaline environments that
would dehydrate other cells, and in atmospheres rich in
toxic gases like methane or hydrogen sulfide that would kill
most other organisms. These harsh environments may be
similar to the conditions present on the early Earth, when
life first began. It is likely that bacteria evolved to dwell in
these harsh conditions early on and have retained the ability
to exploit these areas as the rest of the atmosphere has
changed.