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Thread: Dating the origin of life

  1. #1 Dating the origin of life 
    SHF is offline
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    Sep 2012
    I often read that the origin of life on earth was about 3.6 billion years ago. How did we arrive at this figure? What are the margins of error? What is the level of certainty?

    Is it simply a prediction based on our understanding of changing geochemical conditions since Earths formation and at what point the earth would have been hospitable to the formation of biological life? i.e. there had to have been cooling to the point that water was present / conditions supporting self-sustaining series of reactions (or whatever conditions were need for the ‘prebiotic soup theory’ or the ‘metabolist theory’ or whatever).

    Is it about triangulation of genomes? (although that would only go back so far I guess, given there is a preDNA biological world and a preRNA biological world of prototypical biological replicators).

    When I wikipedia ‘abiogenesis’ the photo caption to the side notes a 2002 paper suggesting 3.5 Ga geological formations in Glacier National Park containing fossilised cyanobacteria microbes. The same Wikipedia page (Abiogenesis - Wikipedia, the free encyclopedia) states:

    “Evidence of the early appearance of life comes from the Isua supercrustal belt in Western Greenland and from similar formations in the nearby Akilia Islands. Carbon entering into rock formations has a ratio of Carbon-13 (13C) to Carbon-12 (12C) of about −5.5 (in units of δ13C), where because of a preferential biotic uptake of 12C, biomass has a δ13C of between −20 and −30. These isotopic fingerprints are preserved in the sediments, and Mojzis has used this technique to suggest that life existed on the planet already by 3.85 billion years ago.”

    Is this the way the calculation has been made (and all the books I see stating ~3.6 Ga get their number from the above)??

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  3. #2  
    Universal Mind John Galt's Avatar
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    Jul 2005
    The two methodologies applied are two of those you have identified:

    1) Chemical fingerprints suggesting biochemical activity. The Issua data are disputed, since some researchers believe inorganic reactions can produce the same results.
    2) Fossils traces. Stromatolites have been identified in rocks around 3.5 to 3.6 Ga. Some of the earlier findings are also disputed.

    Despite the disputes referred to the consensus is that life began on Earth between 3.6 and 3.9 billion years ago. i.e. Immediately after the end of the Late Heavy Bombarment period.

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