February 17th, 2009at 11:14am Posted by Eli
Scientists are exploring the possibility that “alien” life may have evolved right here on Earth:
If life arose not just once, but multiple times on Earth, life as we don’t know it could be here on our own planet, perhaps using different chemical processes than we’ve ever seen before. And because scientists have only studied a tiny slice of the world’s microbes in depth, the microscopic remnants of a second (or third or fourth) biogenesis could be hiding right beneath our noses.
“If life did happen many times, there could be something like a shadow biosphere that either was, or is, all around us,” Arizona State Univeristy astrobiologist Paul Davies said here Sunday at the American Association for the Advancement of Sciences meeting. “It’s entirely possible that some fraction of microbial life could turn out to be alien or ‘weird’ life as we prefer to call it.”
Davies’ contention challenges the relatively accepted orthodoxy that life arose once on Earth and colonized the entire planet. This weird life would the best possible analog for extraterrestrial life. Finding it, or even creating it in a laboratory, would give researchers clues about both how life began on Earth and how common life is on other planets. If a second sample of life on Earth exists, it would raise the probability for extraterrestrial life and help provide knowledge about other plausible structures for life in the universe.
This strange life could be far more simple than the life that we know after 4 billion years of evolution, or it could use different chemical machinery to carry out the processes of life, like using arsenic in the same way that all living things we know use phosphorous.
Truly “weird” life… would function using different elements or have different basic genetic material. Stumbling upon this life could be quite difficult, as the likeliest spot for one of these life forms would appear to be one of the thousands of unexplored deep sea vents. But Davies thinks a fairly simple endeavor could determine whether arsenic-using life exists: Find a virus that incorporates arsenic and you have suggestive evidence that the cells exist.
“The idea I did have is that if there are weird cells lurking somewhere, that they’ve probably got weird viruses that prey on them. Viruses get everywhere. The oceans are like virus soup,” Davies said. “Just looking for viruses with arsenic in there seems fairly straightforward.”
I can’t see any reason why life could not have arisen multiple times on Earth, or in parallel in different isolated environments. If anything, it seems kind of odd that it wouldn’t. Unless the spark of life really is a truly rare occurrence and it’s a minor miracle that it happened at all. I don’t think we know quite where that threshold is – does it just require the right conditions, or is there a large element of chance involved as well?