I've worked out the hyperlink thing, but am not sure if the links will work since I'm going through the ANU Library subscription service for New Scientist. So I've included the text here.
Did life begin on a radioactive beach?
Life's ingredients could have emerged among the radioactive sand grains of a primordial beach laced with heavy metals and pounded by powerful tides...
DID life on Earth begin on a radioactive beach� That's the claim of one astrobiologist, who says that life's ingredients could have emerged from the radioactive sand grains of a primordial beach laced with heavy metals and pounded by powerful tides.
Any origin of life theory needs to explain how the building blocks of cells – such as amino acids and sugars – assembled into complex molecules, and how certain elements came to be incorporated. Though radiation might seem an unlikely source to kick-start such processes because it breaks chemical bonds and shatters large molecules, including DNA, it can provide the chemical energy needed to produce life's building blocks.
Natural “nuclear reactors” were active in the past, such as the uranium ore seam in Oklo, Gabon, which regulated the fission of uranium in a similar way to nuclear-powered submarines (New Scientist, 6 November 2004, p 12). However, conditions at the time life emerged were thought to be unsuitable for concentrating uranium sufficiently to form a reactor that would provide enough energy to create the molecules necessary for life. For instance, a lack of atmospheric oxygen would have prevented uranium becoming water-soluble, so it could not be transported and deposited in rock to form seams like the Oklo reactor.
Now Zachary Adam at the University of Washington in Seattle claims that tidal processes could have concentrated radioactive grains of uranium on a primordial beach, where they may have helped to generate life's building blocks. (Astrobiology, vol 7, p 852). Powerful tides generated by the moon's closer orbit to the Earth compared with today could have sorted the radioactive minerals from other sediments and deposited them along the beach's high-tide mark, he says. According to his computer models, a deposit of radioactive grains could experience the same self-sustaining fission reactions as a seam of uranium.
Adam also designed laboratory experiments with radioactive sand to simulate a beach environment, and found that such a setting would provide the chemical energy to generate some biological molecules in water, such as acetonitrile, which can produce amino acids and sugars when irradiated. Adam says that the radioactive mineral monazite would also release another of life's key ingredients – soluble phosphate – into the regions between the sand grains, making it biologically “accessible” in the water. “Amino acids, sugars and [soluble] phosphate can all be produced simultaneously in a radioactive beach environment,” he says. Furthermore, he says that radioactive actinides such as thorium and uranium could have formed one part of “organometallic complexes” – made up of a metallic ion and an organic molecule. These could have catalysed crucial biological reactions long before the emergence of enzymes.
John Parnell, a geologist at University of Aberdeen in the UK, is intrigued by the theory. “Such a mechanism may provide the crucible for life on any wet rocky planet,” he says, so long as the planet is large enough for the volcanism associated with plate tectonics, which brings radioactive minerals to the surface.
Also in New scientist this week:
FIFTY years ago, evolutionary theory viewed nature through a lens of benevolence: individuals acted for the good of their group, ensuring its survival. This idea, called group selection, did not last out the 1960s. It was swept away by an intellectual revolution which argued that natural selection at the level of genes is what really counts.
This “gene's eye” approach sees attributes that benefit society accruing via bottom-up processes. Altruism, for example, which keeps the wheels of society turning but puts many individuals at a disadvantage, is explained through ideas such as kin selection. This proposes that animals help their relatives in order to pass on shared genes, so what looks like altruism is really the selfish gene in action.
Now, a counter-revolution is being fomented. Late last year, the Harvard biologist Edward O. Wilson co-authored an article in support of group selection (New Scientist, 3 November 2007, p 42). This week, we report that Wilson now thinks kin selection plays an insignificant role in the evolution of colonies formed by social insects (see “Kinship doesn't matter – how insects are altruistic”).
Does this mean evolution itself is in doubt� Certainly not. The debate is akin to physicists questioning the nature of gravitational attraction: nobody disputes that gravity exists, but pinning down its true character should deliver deep new insights.
Wilson has already met serious opposition (see “The evolution of altruism – what matters is gene selection”) and is certain to attract more. Yet such is his standing that we are almost certainly in for a thorough re-examination of group and kin selection. If this elucidates evolutionary processes and gives us that extra insight, it can only be a good thing.
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