Another *Life Might Be Rare* paper

[marcus]

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.

http://arxiv.org/abs/1107.3835
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.

 

[Drakkith]

Thanks marcus!

 

[Nik_2213]

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...

 

[Chronos]

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.

 

[pmacias]

Thank you for sharing this paper and your thoughts on it. I appreciate the critical evaluation of evidence and the importance of considering different perspectives. While this paper may not definitively prove that life is rare or not rare, it does bring up important points to consider in our understanding of the probability of abiogenesis.

The authors make a valid point that the early emergence of life on Earth does not necessarily imply a high probability of abiogenesis. This is because the Bayesian analysis shows that the prior probability chosen for the abiogenesis parameter has a dominant influence on the computed posterior probability. In other words, the initial assumption we make about the probability of abiogenesis greatly affects our final conclusion.

I also appreciate the authors' use of a simple model to estimate the probability of abiogenesis, as this allows for a more transparent and reproducible analysis. However, as with any model, there are limitations and assumptions that should be considered.

Overall, this paper highlights the need for further research and investigation into the probability of abiogenesis, as well as the importance of carefully choosing our assumptions and priors in Bayesian analyses. As scientists, it is important to continue to question and challenge our understanding of the world around us, and this paper contributes to that ongoing discussion.