-----Original Message-----
From: Daniel R. Zeigler, Ph.D. <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Date: Thursday, February 22, 2001 9:20 AM
Subject: RE: Microoganisms and Phylogeny
>
>
>> I doubt "cross-pollination" will ever be a legitimate concern.
>
>I basically agree with both Jayme and Michael on this point. A truly alien
>biochemistry might very well be fundamentally similar to our own (see N.
>Pace. 2001. "The Universal Nature of Biochemistry" Proc Natl Acad Sci USA
>98:805-808). I personally feel that all cellular life is likely to be
based
>around nucleic acids, proteins, lipids, and their building blocks. Even
so,
>it seems extremely unlikely that all the details of an
independently-derived
>genetic code would wind up being close enough that an alien gene would
>function inside a terrestrial organism. *If* Earth seeded Mars with
>microbes via impact debris, however, or if Mars seeded Earth, then the
>genetics would probably be close enough. That's not to say that such
>cross-pollination would necessarily even be bad. It happens on Earth all
>the time. I'm quite optimistic that the actual risk is very low. But
since
>no one can say the risk is zero, and since one mistake could be fatal,
we're
>going to have to be very, very careful.
>
>Dan Zeigler
This is the sort of thing Barry DiGregorio is so worried (or panicked)
about; I've been engaged in a semi-friendly debate with him for quite some
time. My own feeling is pretty much in accord with Dr. Zeigler's -- if Mars
does still have life, natural metorite transfers are sending samples of it
over here every few hundred thousand years. But we don't know how much harm
those new arrivals did at the time to parts of Earth's ecosystem that we
would consider valuable; and so care in the handling of human-returned
samples is definitely called for (contrary to Robert Zubrin's brassy
confidence).
In that connection, I'm very uneasy about NASA's current tentative plan to
have the Mars sample-return capsule land directly on Earth. It's designed
as a non-parachute "puffball" structure that supposedly can withstand any
impact on hard or jagged rocks; but what if it lands in the ocean or some
other place where it's never found and eventually corrodes open? I much
prefer retrieval in orbit by the Shuttle (which need not also entail an
expensive orbiting quarantine lab -- the sample canister could simply be
loaded into a very thick-walled crashproof cask with good locator gear,
which the Shuttle could easily carry in addition to carrying out another
orbital mission). I also favor coating the outside surface of the small
sample-return container itself with an ignitable compound to heat-sterilize
any dust particles stuck on the outside of the canister.
And -- as Tim Stevens indicates -- arguably the discovery of Europan life
would actually be far more important scientifically than the discovery of
Martian life. Martian life may very well have seeded Earth via meteorite
(or vice versa), so even if we find it there it would not constitute proof
that life is common in the Universe -- it could have happened as a single
extremely rare event on Earth or Mars, which then seeded the other world.
But if life is found on Europa, it almost certainly was a separate event,
and therefore represents virtual proof that life does very often evolve in
the Universe.
Bruce Moomaw
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