Saturday, March 06, 2010

Are There Alternate Biochemistries Lurking On Earth?

Mono Lake has a bizarre, extraterrestrial beauty. Just east of Yosemite National Park in California, the ancient lake covers about 65 square miles. Above its surface rise the twisted shapes of tufa, formed when freshwater springs bubble up through the alkaline waters.

Felisa Wolfe-Simon, a geobiologist, is interested in the lake not for its scenery but because it may be harbouring alien life forms, or “weird life”. Mono Lake, a basin with no outlet, has built up over many millennia one of the highest natural concentrations of arsenic on Earth. Dr Wolfe-Simon is investigating whether, in the mud around the lake or in the water, there exist microbes whose biological make-up is so fundamentally different from that of any known life on Earth that it may provide proof of a shadow biosphere, a second genesis for life on this planet.

Arsenic is chemically close to phosphorus. While phosphorus is a primary building block of life on Earth — an essential component of DNA and ATP, the energy molecule — arsenic is a deadly poison. In Mono Lake there are micro-organisms that live with arsenic. But they don’t incorporate it into their biology.

Dr Wolfe-Simon has theorised that there may be life that chose an “evolutionary pathway” to utilise arsenic. If such microbes existed, it could suggest that life started on our planet not once but at least twice. In turn this would help to support the idea that life is much more likely to have started elsewhere in the galaxy.

“There is life ‘as we know it’ and there is life ‘as we don’t know it’. What would that look like? I am trying to give us a framework to work with to help us look for what ‘we don’t know’, the particular framework of arsenic,” she says.

Dr Wolfe-Simon has taken samples from the mud and the waters of the lake and is performing a series of multiple dilutions — hugely increasing the levels of arsenic and reducing residual phosphorous to zero. She adds sugar, vitamins and other nutrients to encourage organisms to grow and tests the results.

Her experiments are not yet over but she is quietly pleased with the progress she is making. “We have some very exciting data,” she says. The results should be published by the end of this year.

hmmmm. What do you guys think?

Exciting data can be interpreted in many ways.

1 comment:

Raphite1 said...

Looking forward to seeing her results. Assuming that she does find something arsenic-based, I suppose there are three possibilities: (1) It evolved from "common" forms already existing, (2) it's the product of a relatively recent abiogenesis process in the lake itself, or (3) it's a surviving clade of arsenic-using organisms that have been around for eons.

Instinctively, Hypothesis (1) seems most likely to me. I'm sure studies would be attempted in order to compare "chance of accumulating enough adaptations to functionally replace phophorus with arsenic" versus "chance of a biogenesis event occurring," but the numbers used in such a study would surely be highly arbitrary.

Hypothesis (2) seem extremely unlikely, since the lake is such a relatively small and uncomplex system (I'm assuming; I really don't know anything about it). If the lake is still populated by "common" forms of life sporting billions of years of adaptations, how would any proto-organisms stand a competitive chance? I suppose that an arsenic-laden lake may have more available niches. If it can be demonstrated that life did independently develop in the lake, the discovery would be a huge step forward in uncovering the processes that permitted abiogenesis on Earth in general. A convenient little "microworld" with far fewer variables, and a less deep timescale.

Hypothesis (3) seems like it would be difficult to disprove if someone were hoping to advance Hypothesis (2). Just because the rest of the world isn't as arsenic-heavy as the lake doesn't mean that arsenic-based life necessarily couldn't thrive elsewhere. If arsenic-using life existed commonly in the past (or still does), the correct default presumption would seem to be Hypothesis (1).