[meteorite-list] Carbonate Globules Found in Volcano Rocks Similar to ALH84001

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Jun 23 20:25:37 2006
Message-ID: <200606240023.RAA03740_at_zagami.jpl.nasa.gov>

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

>From the earth's bowels
The Statesman

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.)
Received on Fri 23 Jun 2006 08:23:18 PM PDT