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Dave McKay Talk at JPL



Dave McKay gave a lecture here at JPL on April 15 about the latest information
about the possible microfossils in ALH84001.  If you will remember, Dave McKay
is one of the original co-authors of the now famous August 1996 paper in 
Science  magazine.  

In his talk, McKay first gave a review of the evidence for and against the
microfossil case in ALH84001, though not surprisingly most of the evidence he 
presented was in favor of possible microfossils.  He also presented new evidence
of what what he is claiming to be biofilm present in the meteorite.  He showed
photos of known biofilm material in Earth rocks, and compared them with
similar looking structures from ALH84001 (they do look somewhat the same,
but I wouldn't necessarily call them an exact match).  He said
that to date there is no "smoking gun" evidence in favor of life in the
meteorite, nor is there any "smoking gun" evidence against life in the
meteorite.  The issue probably won't be resolved until we actually return
a sample from Mars for analysis.  

He also stressed that the microfossils only exist in the carbonate globules
in ALH84001, and no evidence for life is found in the other parts of the 
meteorite.  This is an important point as several papers published that 
provided evidence against life in the meteorite were looking at the 
non-carbonate portions of the meteorite.  McKay said that the best evidence 
against the microfossils is the finding of terrestrial contanimation in
the meteorite, and readily admits there is such contanimation, but insists 
the carbonate globules are of Martian origin.  McKay also mentioned that 
carbonate globules were recently found in a Tunisia meteorite, which would 
be reported in Science magazine, and this finding strengthens his case.  
Looking on the Web, I found the title of the article in the April 17 issue 
to be "Formation of Carbonates in the Tatahouine Meteorite" by J. Barrat, 
P. Gillet, C. Lecuyer, S. Sheppard and M. Lesourd.  I haven't read the 
article yet.  Tatahouine is a diogenite, a basaltic achondrite (all of the
Mars meteorites are basaltic rocks),  and is one of the more easily 
obtainable diogenites on the market.

Ron Baalke