Thursday, December 02, 2010

Arsenic and Old (definitions of) Life

I'm a very excited bunny. In just a few hours, NASA will be giving details of an extraordinary find; a wholly new kind of life form, discovered here on Earth, that overturns the accepted view that all life uses phosphorous. This is a bacterium that uses deadly arsenic instead.
I say 'accepted view' ... It's the view of astrobiologists. As I've blogged about in the past, there are two distinct camps when it comes to thinking about aliens. The astrobiology camp concerns itself with looking for Earth-like planets that exist within the so-called 'Goldilocks Zone' around a star. Therefore, the temperature allows for liquid water etc. Meanwhile there's the exobiology camp that takes a more flexible approach. Instead of looking for worlds where life as we know it could exist, they look at environments and ask 'What would life have to be like to live here?' Exobiology was always seen as more of a fringe science. However, a series of discoveries over the past decade has shown that 'life as we don't know it' is pretty damned common.

First there was the astonishing revelation that whole ecosystems exist around volcanic 'black smokers' on the seabed that derive all of their energy from chemicals rather than from the Sun. That was a surprise. Then there are the extremophiles we've discovered; microorganisms that can exist in environments thought to be entirley hostile such as inside rock, in molten lava, frozen in supercold ice or even in space. And just a few months ago (see here) creatures called loriciferans were found living below the Greek seabed that don't need oxygen at all - another first.

And now we've found a creature that doesn't conform to our understanding of what the building blocks of life should be. All life on Earth is made of six components: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur. Everything from an amoeba to a blue whale has the same basic structure. But not this bacterium. Discovered in the poisonous waters of Mono Lake, California, it uses arsenic instead of phosphorous, something that was thought to be completely impossible. The implications of this discovery are enormous.

It means that life on other worlds could be even more bizarre than we could possibly imagine. Take that astrobiologists.

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