David S. Spiegel, Edwin L. Turner
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, curious 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. Although terrestrial life's early emergence provides evidence that
life might be common in the Universe if early-Earth-like conditions are, the
evidence is inconclusive and indeed is consistent with an arbitrarily low
intrinsic probability of abiogenesis for plausible uninformative priors.
Finding a single case of life arising independently of our lineage (on Earth,
elsewhere in the Solar System, or on an extrasolar planet) would provide much
stronger evidence that abiogenesis is not extremely rare in the Universe.
View original:
http://arxiv.org/abs/1107.3835
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