Thanks to The Daily Grail I saw a rather interesting article from Astrobiology Magazine on extremophiles and how their existence here on Earth may play into the search for life on other planets. Titled "Earth's Hidden Biospheres" it discusses the recent discovery of a colony of microbes far below the surface, in a mine in South Africa, which lived off of sulphur compounds formed by radioactive decay from the surrounding rocks, as well as other recent extremophile discoveries, and what their existence could mean for life elsewhere in the universe. While this has been a fairly hot topic lately, I found their concluding paragraph to be particularly interesting.

What are all these diverse organisms doing? In a sense, they are not very successful, since they are far outnumbered by more familiar species. Yet they persist in small numbers. Perhaps they represent a kind of natural back-up system or reserve force that can swing into action if environmental conditions change in ways that threaten the dominant ecosystem. They could be part of lifes strategy to survive even catastrophic environmental changes. The next challenge is to estimate the global patterns in this rare biosphere and to begin to characterize its individual species.

Perhaps this is a logical and obvious conclusion to most people, but I have to admit I'd never really thought of these very different forms of life as being a potential back-up system should the ecosystem that the predominant life forms live in become contaminated in some way. If this were to happen in any complex system of life, on any planet, then maybe finding small pockets of live microbes on another planet would signal the existence a larger biosphere in the past. Perhaps one that may have suffered some kind of disaster, which in turn ended the lives of a predominant life form leaving only a trace of life leftover.