Hanson has a post on this. It seems to me that the chemical signature matching ancient life much better than recent life is really quite strong evidence.
I like this quote from Hanson:
I’d bet these commentaries will mostly say this is interesting but doubts remain, that this evidence is too ordinary to support its “extraordinary” conclusion, and yet they’ll refuse to bet on the subject. How sad is that?
I'd really like to see Hanson put his money where his mouth is as in a clear, unambiguous and publicly available way. A decent figure (>=$1,000) at odds he considers favorable after considering this evidence and all his priors. That would be powerful advocacy of his most notable economics related there...
http://journalofcosmology.com/Life100.html
http://www.wired.com/wiredscience/2011/03/aliens-riding-meteorites-arsenic-redux-or-something-new/
http://news.ycombinator.com/item?id=2293643