[meteorite-list] From the earth’s bowels

From: Mike Groetz <mpg444_at_meteoritecentral.com>
Date: Fri Jun 23 07:43:24 2006
Message-ID: <20060623114316.18636.qmail_at_web32903.mail.mud.yahoo.com>

http://www.thestatesman.net/page.news.php?clid=24&theme=&usrsess=1&id=121054

>From the earth?s bowels

A meteorite from Mars was found to contain tiny
mineral spheres that, some argued, were produced by
living organisms. Now researchers working in the high
Arctic have found similar mineral features ~ produced
not by microbes, but by a volcano. SP Sarin reports

WELL above the Arctic Circle at the northern tip of
Norway lies Hammerfest. A ship headed north from this
city will run into a group of islands called the
Svalbard archipelago before its carries on to the
polar ice cap. For the two summers now, scientists in
the largest of these islands are studying an
environment that promises to shed light on a meteorite
that was found at the opposite end of the earth ? in
Antarctica.
This meteorite ? ALH84001 ? started out as an
unremarkable piece of volcanic rock that formed about
4.5 billion years ago on Mars. About a billion years
later, its interior was chemically altered through
interaction with water. Thereafter, it remained on the
Martian surface until about 16 million years ago when
a massive impactor ? a comet or asteroid ? slammed
into Mars and spewed material into space at such
tremendous velocity that some of this, ALH84001
included, was able to escape Mars? gravity. Drifting
through interplanetary space for millions of years,
the meteorite eventually collided with earth about 13
thousand years ago. In 1984 it was discovered by
meteorite hunters in the Allen Hills region of
Antarctica.
ALH84001 gained international fame when scientists at
the National Aeronautics and Space Administration?s
Johnson Space Centre announced in 1996 that it
contained evidence of life ? Martian life. Miniscule
structures within the meteorite looked similar to
fossilised bacteria seen on earth. A form of magnetite
(iron oxide) was detected in the meteorite which, on
earth, is produced only within the bodies of certain
bacteria. Researchers also found unusual microscopic
carbonate globules which they believed were formed by
living organisms.
Carbonates are common on earth. England's famous White
Cliffs of Dover, for example, are made from calcium
carbonate, or limestone. But ALH84001?s carbonates
were far from being common limestone; they were
unique. Scientists had no way to tell where on Mars
the meteorite had come from, or what its history had
been prior to being cast into interplanetary space.
There was no way of knowing for certain how the
carbonate globules had formed. But their unusual
appearance, one of several distinctive features of the
rock from another world, led the JSC researchers to
conclude that living organisms had once made their
home there.
Members of the scientific team who made the original
announcement still believe ALH84001 contains evidence
of Martian life. Most researchers, however, now think
that its various microscopic features can be explained
purely by geologic and chemical processes. Recent
discoveries made in Svalbard bolster that majority
opinion.
Although ALH84001?s carbonate globules were novel at
the time the meteorite was discovered, scientists have
since discovered that rocks in Svalbard contain
carbonate globules remarkably similar to those found
in ALH84001 and they were anxious to learn what they
could about how the Svalbard carbonate globules
formed. Most can only speculate about the formation
billions of years ago and millions of miles away, but
in Svalbard, says Andrew Steele, ?the geology's in
context?.
Steele, who is with the Carnegie Institution of
Washington, is a member of the Arctic Mars Analog
Svalbard Expedition, an international team of
scientists who for the past three years has been
studying the Svalbard environment. The major aspect of
their work is to test life-detection instruments that
will be used on future missions to Mars. But it was
the discovery of Svalbard's carbonate globules that
first caught their attention.
?Originally, we didn't set out to try and confirm or
refute whether the carbonate globules in ALH84001 were
formed by biology or not. We basically went up there
to look at the context and find out just how these
things are formed on earth, and then try to draw some
conclusions about their formation mechanisms on Mars,?
says Steele.
The context is a volcano ? Sverrefjell ? that erupted
about a million years ago and forced magma up through
an overlying glacier. The carbonate globules in the
Svalbard rocks were found embedded inside material
that was spewed out when the volcano erupted. An
analysis of the material surrounding the globules ? a
mineral known as olivine because of its dull green
color ? showed that it came from the earth?s mantle,
some 40 to 50 km beneath the surface. Before the
eruption, it was in a molten state, deep underground.
Within a few days of being ejected onto the surface,
it had cooled and hardened in the freezing glacial
environment above ground. During this cooling process,
the carbonate globules became deeply embedded within
the surrounding rock.
?This is an abiotic production method,? says Steele.
No living organisms could have been present in the
molten subterranean depths. Nor could microbes have
colonised the molten material in the short span of a
few days during which the rocks cooled and hardened,
sealing the globules deep within.
Armed with the knowledge that the Svalbard globules
were formed abiotically, Steele and his colleagues
performed a painstaking comparison between them and
the ALH84001 globules. Using one of the most
sophisticated instruments of its type in the world, a
Raman spectrometer, the Amase team examined thousands
of tiny spots both within samples of ALH84001 and
within rocks collected in Svalbard. The Raman
spectrometer enabled them to catalog in detail the
mineral components in the carbonate globules within
the two rocks. They found a high degree of similarity.
?That doesn't mean to say that (the Svalbard globules)
are exactly the same as the Martian globules and are
formed in exactly the same conditions,? says Steele,
?but it gives us a window into that formation process.
There is a formation mechanism for them that doesn't
rely on biology.?
The ALH84001 saga is far from over. There will
undoubtedly be discussions about its various unusual
features for many years to come, but by showing how
carbonate globules, similar to those in the Martian
meteorite, formed without the involvement of living
organisms, Steele and his team have made less
compelling the argument that the visiting rock from an
planetary neighbour contains evidence of life.
(The author is a geologist who works in the USA.)



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Received on Fri 23 Jun 2006 07:43:16 AM PDT