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Another *Life Might Be Rare* paper

  1. Jul 20, 2011 #1


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    Don't expect to learn a lot. They don't prove life is rare and they don't prove it isn't rare. Basically they argue that the evidence we have so far (life's quick appearance on the earth not long after the surface temperature stabilized in the liquid water range) is not sufficient. They argue that life could still be rare even though in this one case it appeared soon after liquid water conditions got established.

    Life might be rare despite its early emergence on Earth: a Bayesian analysis of the probability of abiogenesis
    David S. Spiegel (1), Edwin L. Turner (1, 2), ((1) Princeton, (2) IPMU, University of Tokyo)
    (Submitted on 19 Jul 2011)
    Life arose on Earth sometime in the first few hundred million years after the young planet had cooled to the point that it could support water-based organisms on its surface. The early emergence of life on Earth has been taken as evidence that the probability of abiogenesis is high, if starting from young-Earth-like conditions. We revisit this argument quantitatively in a Bayesian statistical framework. By constructing a simple model of the probability of abiogenesis, we calculate a Bayesian estimate of its posterior probability, given the data that life emerged fairly early in Earth's history and that, billions of years later, sentient creatures noted this fact and considered its implications. We find that, given only this very limited empirical information, the choice of Bayesian prior for the abiogenesis probability parameter has a dominant influence on the computed posterior probability. Thus, although life began on this planet fairly soon after the Earth became habitable, this fact is consistent with an arbitrarily low intrinsic probability of abiogenesis for plausible uninformative priors, and therefore with life being arbitrarily rare in the Universe.
    10 pages, 5 figures, submitted to PNAS

    FWIW Edwin Turner looks like a thoroughly creditable guy. 95 papers on arxiv going back to mid 1990s when he seems to have been working with Abe Loeb at Princeton. Has collaborated with other worldclass people like David Spergel (not to be confused with the current co-author Spiegel). Also Marcy and Butler (exoplanet search leaders.) For me this carries some weight. But maybe you think the conclusions are mild enough that it doesn't really matter much. See what you think.
    Last edited: Jul 20, 2011
  2. jcsd
  3. Jul 20, 2011 #2


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    Thanks marcus!
  4. Jul 20, 2011 #3
    That's a bit like the old Windows(TM) analogy-- 'Higher' life can only get so far before the system crashes...

    You may invoke too-frequent mega-volcanoes, incoming asteroids, near-by supernovae etc etc...

    My preferred explanation is that the funding was cut...
  5. Jul 21, 2011 #4


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    Earth is admittedly a small sample size, and the sequence of events leading to the emergence of sentient life [i.e., humans] appears unique, but again, also a small sample size. If we find any form of life, as we know it, elsewhere in the solar system, probabilities change. The fermi paradox remains in play, but, I suspect the combined technological and resource challenges of interstellar travel also need to be considered.
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