This is interesting. Yes. Really.
I said so.
Second Genesis: The search for shadow life While some researchers are attempting to create brand new life in the lab, others are searching for alien life on Mars and, eventually, elsewhere in the solar system. This burgeoning field of astrobiology has a less well-known offshoot right here on Earth: the search for a "shadow biosphere"- a second, independent form of life unrelated to sort we know (Astrobiology, vol 5, p 154).
After all, many astrobiologists now think that given the right conditions any sufficiently complex molecular soup has a good chance of generating life if it simmers long enough. If that's so, it seems plausible that life may have arisen on Earth not once, but several times. New origins of life are unlikely today, because existing life would gobble up any aggregations of prebiotic molecules before they could edge over the threshold. However, opportunities for the origin of life may well have existed for long periods on the early Earth. Some of these origins may have been dead ends, out-competed by other life forms - but others could still be living among us, unnoticed.
Check this:
One promising avenue is to explore extreme environments that are beyond the reach of conventional life, such as ultra-dry deserts, ice sheets, the upper atmosphere or the hottest hydrothermal vents (see
The most extreme life-forms in the universe)
Another is to devise ways of detecting alternative biochemistries. In the first and so-far only experiment of this kind, Richard Hoover, a microbiologist at NASA's National Space Science and Technology Center in Huntsville, Alabama, went looking for "mirror life". Normal organisms use right-handed sugars and left-handed amino acids almost exclusively, and eschew their mirror-image equivalents. But what if shadow life developed the opposite preference? Hoover and his colleague Elena Pikuta created nutrient broths containing only left-handed sugars and right-handed amino acids, inoculated them with unusual extremophile microbes and waited to see if anything grew.
This may not raise any eyebrows here but it's very significant. Up until now it has been assumed that no life forms on Earth could metabolise left-handed sugars and right-handed amino acids. It's the biological analogy of matter and anti-matter, in loose terms, or of walking around on your head with your feet in the air.
This news raises the definite possibility of life forms fundamentally different to any we knew of. Literally, "it's life, Jim, but not as we know it".
The whole article (linked from the title) is worth checking out.
Also this.
Topic: Second Genesis: The search for shadow life