Here Be Dragons

THE INCREDIBLE SHRINKING MARTIANS
from the weathered samples displayed carbonate "pancakes" as well as
tiny rods and spheres resembling the "microfossils" in ALH84OOI.
Even in the arid Sahara, apparently, occasional wetting can lead to the
deposition of carbonates and microbelike structures.
All in all, the hypothesis of David McKay's group, that ALH84OOI
was once home to martian microbes, seems quite a bit less compelling
than when it was first put forward. The only piece of evidence that still
has strong adherents is the magnetite crystals. When we ask Chris
McKay about his namesake's findings, he is noncommittal. "I'm prochoice
rather than pro-life," he says. "Their evidence is consistent with
life, but it's consistent with a lot of other processes too. They haven't
proven their case, and their critics haven't proven them wrong either."
To Chris McKay, the main significance of the martian meteorite is to
highlight the importance of continuing the program of exploration
begun by the Viking landers.
"If there's life on Mars today, it's probably deep underground," he
says. "There could be organisms that live offCO 2 [carbon dioxide] and
hydrogen, like the ones in the Columbia River basalts. There could be
an ecosystem built around them. But to find them, you'd have to drill
down through the permafrost—kilometers, probably. It would be a
tough job. Maybe you could use ground-penetrating radar to find
places where liquid water comes close to the surface. You might even
be able to find a little vent, a geyser, where it comes all the way up to
the surface: Mars's 'Old Faithful.' But that's unlikely."
McKay is involved in planning missions to test for the possibility of
life on Mars, and his assessment is that it's not cost-effective to be
looking for life that may currently exist beneath the martian surface.
"My bias is towards finding fossilized organisms in ancient lake beds.
Wherever water pooled on the surface, life may have existed in ice-covered
lakes, as in the Antarctic lakes on Earth. Those are good places to
look for fossils because the sedimentary materials would be there on
the surface. And right now, we can point to places that were lake beds,
like the Gusev Crater in the southern hemisphere. They're the most
promising for a near-term mission."
Imre Friedmann makes a slightly different suggestion. He proposes
that if life ever existed on Mars, it would have been driven into habitats
like those of his Antarctic endolithic communities (see Chapter 2) as
the planet cooled and dried out. 22 The trace fossils of these communities
might still be detectable on rock surfaces.
McKay and most others in the field believe that the biological explo-
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