"A Bayesian Analysis of the Astrobiological Implications of the
Rapid Emergence of Life on the Early Earth"
(Ed Turner, Princeton University)

ABSTRACT: 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 abiogenesisis high, if starting from young-Earth-like
conditions. This argument is revisited quantitatively in a Bayesian
statistical framework. Using a simple model of the probability of
abiogenesis, a Bayesian estimate of its posterior probability is
derived based on the datum that life emerged fairly early in Earth's
history and that, billions of years later,sentient creatures noted
this fact and considered its implications. Given only this very
limited empirical information, the choice of Bayesian prior for the
abiogenesis probability parameter has a completely dominant influence
on the computed posterior probability. Thus, although life began on
the Earth quite soon after it became habitable, that fact is
statistically consistent with an arbitrarily low intrinsic probability of
abiogenesis for plausible uninformative priors and, therefore, with life
being arbitrarily rare in the Universe. The presentation will emphasize
generic statistical properties of problems of this general character
as well as the particular topic in question.

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Last-modified: 2013-11-20 (水) 11:11:54 (1404d)