>Notwithstanding the theological implications of life on other planets,
>or even whether this space chunk actually contains remnants of early
>primitive life, how do we know this meteorite came from Mars? Why not
>planet Earth, for example?
I have just read the article in _Science_ that has been the focus of the
recent discussion in the media. It is entitled "Search for past life on
Mars: Possible relic biogenic activity in Martian meteorite ALH84001." I
would encourage everyone interested in this issue to read the article for
themselves. It can be viewed on the _Science On-Line_ webpage
(http://science-mag.aaas.org/science/).
The interpretation of this particular meteorite as coming from Mars was
based on previous studies (These studies are listed in the footnotes). It
belongs to a class of meteorites believed to have come to Earth from impact
events on Mars. The abundances and isotopic compositions of gases trapped
in glassy inclusions in these meteorites have one-to-one correlations with
those of the Martian atmosphere as measured by the Viking landers.
My impression of this study is that it is very thorough and has examined
all the likely confounding factors. Its very tentative conclusions seem
reasonable. Much more evidence (presumably gathered from Mars itself)
would be required to move this from reasonable speculation to a persuasive
conclusion.
Keith
Keith B. Miller
Department of Geology
Kansas State University
Manhattan, KS 66506
kbmill@ksu.ksu.edu
http://www.ksu.edu/~kbmill/