This is in response to Robert's post at:
http://www.habitablezone.com/space/messages/12915.html

Robert wrote:
I hate myself for this. I'd rather the odds go up, but what can I do? I think that perhaps Dr. Levin was a tad optimistic in assigning a value of 1 to so many probabilities in the chain.

What's your take, Alex? Is this just a parlor game like the Drake Equation?

Alex writes:
Probably, but I'll refrain from commenting on Levin's "logic", such as it is. However, if one has been following the literature recently one will note that Levin's SPIE abstract downplays the signficance of a paper that attempts to quantify (much better than Levin has) the problem of Mars to Earth exchange. Along with the famous Drake Equation, we now have the Clark Equation for the "probability of a successful transplant to planet B of viable organisms due to any given hypervelocity impact onto planet A":

P(AB)=P(biz)*P(ee)*P(sl)*P(ss)*P(se)*P(rel)*P(st)*P(sp)*P(efg)*P(sc)

From Benton C. Clark, Planetary Interchange of Bioactive Material: Probability Factors and Implications, Origins of Life and Evolution of the Biosphere 31 (1/2):185-197, February 2001.

A PDF can be downloaded from:
http://www.wkap.nl/sample.pdf?268519

Alex R. Blackwell
University of Hawaii