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Hello Everyone,

In February of this year, Ron forwarded a Stanford University report on
ALH84001 titled "Latest Research Casts New Doubt On Evidence For Fossil Life
In Martian Meteorite."  The report summarized two articles which appeared in
the January 16, 1998 issue of  "Science." The May/June "Planetary Report"
(published by the Planetary Society) contains a brief synopsis of these
reports, as well as a rebuttal by McKay et al.  For the benefit of those who
are not members of the Planetary Society or otherwise I have not read the
articles (and rebuttal), I will summarize them here.

If you are familiar with these studies you may want to click on delete now.

Gene McDonald summarizes the two reports in Science.  McDonald writes that J.
L. Bada, D.P. Gavin, G.D. McDonald (the same), and L. Becker looked at the
amino acids contained within the rock.  Specifically, using liquid
chromatography, the researchers compared the amino acids found in life on
Earth with those not found in life on Earth but present in carbonaceous
chondrites "that have struck Earth and Mars throughout time."  The team found
low levels of some amino acids used by life on Earth but found no non-
biological amino acids.  As well, the distribution of amino acids in ALH84001
was similar to that in ice found in Antarctica, and the "handedness" of the
biological amino acids were almost entirely the same (left) as that used in
proteins on Earth. McDonald states that handedness is equally distributed in
carbonaceous chondrites, thus the conclusion is that the most likely source of
the amino acids found in ALH84001 is terrestrial contamination by biological
material in Antarctica.

The second paper which appeared in "Science" was authored by A. J. T. Jull, C.
Courtney, D. A. Jeffery, and J. W. Beck.  In this paper, Jull. et al. analyzed
carbon isotopes in the organic and carbonate material in ALH84001.   Using a
fractionization process to separate organic and carbonate-associated carbon,
the researchers tested the organic carbon for its ratio of carbon-13 to
carbon-12.  They found that the ratio for these two isotopes "was
indistinguishable from the ratio on terrestrial biological material."  In
addition, the authors note that the organic carbon contained significant
amounts of carbon-14 and Jull and colleagues determined that the radio-carbon
age of the organic material in ALH84001 is between 5,000 and 12,000 years.
Now, comic-ray analysis of the rock indicates that it was ejected from Mars
approximately 14 million years ago and that it has resided in Antarctica for
approximately 13,000 years as measured by radioactive decay of elements
produced while the rock was in space.  Thus the carbon-14 analysis suggests
that the organic material found in ALH84001 was due to terrestrial
contamination after it arrived on Earth.  However, the team also noted that a
small part of the total carbon found in ALH84001 did not contain carbon-14,
"which indicates that it was extraterrestrial."

A rebuttal to the above studies was provided by David S. McKay (the team
leader who did the initial analysis), Everett K. Gibson, and Kathie L. Thomas-
Keprta.   McKay and colleagues point out that although the amino acids in
ALH84001 may have been contaminated by Antarctica, the fact that they are
left-handed does not mean that they are necessarily from Earth; perhaps
Martian microorganisms also produced left-handed amino acids.

McKay et al. also point that in their tests for polycyclic aromatic
hydrocarbons (PAHs), it was discovered that PAHs levels in Antarctic ice and
other Antarctic meteorites are much lower than those found in ALH84001.   PAHs
are also less water soluble than amino acids and are less likely to be
transported into the rock from meltwater.  As well, the work by George Flynn
at SUNY-Plattsburgh indicated that the chlorine to bromine ratio in the
carbonate globules and rims was approximately 10,000 to 1.  McKay et al. point
out that this ratio is nearly 100 times that of Antarctic ice.  This suggests
that the carbonate globules in ALH84001 have not been contaminated by the
soluble chlorine or bromine salts in the Antarctic meltwater.  The authors
also point out that it is unclear as to the location of the carbonate globules
that were analyzed by the Bad group.  In other words, the amino acids analyzed
by the Bada may represent near-surface contamination rather than amino acids
from the carbonate globules

With regard to the study by Jull and colleagues, McKay et al. point out that
the results actually support the micro fossil hypothesis.  The authors found a
carbon rich component that did not contain carbon-14 and was not a terrestrial
contaminant.  This component had a carbon-12 to carbon-13 ratio characteristic
of organic carbon made by Earth organisms 

McKay and colleagues conclude that neither paper totally contradict the
conclusions formed by their original analysis "they only make the story more
complex and challenging."  They suggest (wisely, I might add) that the
ultimate data analysis would come with a successful sample return mission. 

-Walter

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