[meteorite-list] More Evidence of Life on Mars Rock? Not So Fast

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:13 2004
Message-ID: <200102280045.QAA00432_at_zagami.jpl.nasa.gov>

http://www.space.com/scienceastronomy/solarsystem/meteorite_analysis_010227.html

More Evidence of Life on Mars Rock? Not So Fast
By Robert Roy Britt
space.com
27 February 2001

After being batted around the solar system like some cosmic softball, a rock
from Mars ended up on Earth thousands of years ago. Now, 17 years after its
discovery, it has become science's most studied stone.

Researchers say the rock, known as the Allan Hills meteorite, provides
compelling evidence that there was life on Mars, at least in the distant
past. Few questions loom larger in space science today. If Mars once had
life, than we humans would be faced with the increased likelihood that life
has sprung up elsewhere, and we that are not alone.

But after five years of intense scrutiny, the scientific community is no
closer to agreement on whether the rock tells us anything.

The meteorite, scientifically known as ALH 84001, reentered the spotlight
yesterday, when researchers said they had developed further evidence of
structures left in the rock by ancient Martian bacteria.

The evidence revolves around tiny structures called magnetite crystals, so
small that millions of them could hide within the period at the end of this
sentence. Researchers suspect these crystals were left behind by bacteria
that aligned themselves to the magnetic field on the Red Planet. While
scientists say they have ruled out the possibility that the structures might
have been created by earthly organisms, a debate continues over the nature
of the magnetite crystals.

A weak argument

The scientists studying the Mars rock "haven't really eliminated the
possibility that these structures are inorganic in origin," said Jack
Farmer, director of the astrobiology program at Arizona State University.
"Their argument has been weak from the beginning."

Ralph Harvey, a geologist at Case Western Reserve University, was part of
the original team that found the rock from Mars stuck in the ice in
Antarctica in 1984. Harvey said he welcomes the new findings, but he thinks
the researchers are going too far with their interpretations.

"I certainly do not consider these findings 'proof' of ancient Martian life
in ALH 84001," Harvey told SPACE.com.

                                   [Image]

     Upper figure: Modern magnetotactic bacteria, one showing a chain of
     magnetite crystals, as seen in the backscattered scanning electron
    microscope. Lower figure: Magnetite crystals and chains of magnetite
  crystals in the Martian meteorite ALH 84001 in the same type of electron
 microscope. One conspicuous chain is indicated by arrows. The diameter of a
          single crystal is approximately one-millionth of an inch.

Harvey called the work interesting, and added that the researchers have done
a good job. But he said neither of the new studies did any tests to explore
the alternative hypothesis that the magnetites might have been created by
some inorganic process. Instead, Harvey said, they have merely stated that
no inorganic process is known to produce similar structures.

"There is currently no known inorganic chemical means of producing these
magnetite crystals with their unique morphologies," said Dennis Bazylinski,
a geobiologist and microbiologist at Iowa State University who coauthored
one of the papers.

"This is a very weak argument," Harvey said. "The truth of the matter is,
nobody has really looked."

Harvey said a scientific theory can only achieve full strength after
alternative ideas have been ruled out. And he says the meteorite has had a
complex history of more than 4 billion years, "including volcanism, impacts,
travel through space, evaporative processes, re-heating, mechanical
disruption, time in the Antarctic ice. We should expect to see a lot of
confusing and mysterious things."

Defense: An extensive search

Kathie Thomas-Keprta, lead author of one of the new papers, responded that
the researchers have taken a more in-depth look at the structure of the
magnetites and have done an "extensive" literature search for other studies
that might show analogous structures created by inorganic means.

"We came up with zero," Thomas-Kperta said in a telephone interview.

Thomas-Kperta said the detail of the team's original paper, published in the
December issue of Geochimica et Cosmochimica Acta, was voluminous and may
not have been read widely or thoroughly by critics.

Meanwhile, the international list of researchers jumping on the Allan Hills
meteorite bandwagon has grown large. Seventeen researchers were involved in
three papers made public yesterday. Much of the research into the rock has
been funded by the National Science Foundation, the Smithsonian Institution
and NASA's Astrobiology Institute.

NASA geologist David McKay, who was involved in the original study of the
Allan Hills meteorite and coauthored the recent paper with Thomas-Kperta,
staunchly defended the work against criticism. But he allows that final
proof for life on Mars is not yet in.

"These shapes and features and properties that we found in the Allan Hills
magnetite have been understood for years to indicate biogenic origin," McKay
said today. "That doesn't mean they couldn't be produced by non-biological
processes."

But McKay argues that no one has succeeded in producing similar structures
via inorganic means, despite serious efforts (one such project is going on
at the Johnson Space Center, where McKay and Thomas-Kperta work).

"At some point you have to...accept that the only way they could be produced
is by biology," McKay said.

Research will continue. McKay expects proof of life on Mars to come within
five years, based on study of a dozen or so Mars rocks found on Earth.

"We're not expecting any one paper or any one line of evidence to convince
people," McKay said. "But we think that over a period of time...people will
be convinced by the evidence, not by us, not by claims in the press."

More rocks, more clues

Meanwhile, more rocks from Mars have been studied by the same researchers
who originally examined the Allan Hills meteorite.

Two meteorites, called Nakhla and Shergotty, showed the same evidence of
microfossils and other remnants of early life as Allan Hills, according to a
team of researchers led by Everett Gibson, a geochemist at JSC.

Gibson is the senior author on a paper discussing Nakhla and Shergotty in
the Feb. 17 issue of journal Precambrian Research.

Studying our own backyard

Many scientists say we won't have proof of life on Mars until we go there,
either with robots or humans, and study some rocks that have a less random
history.

But Farmer, of the ASU astrobiology program, says an ultimate answer may
first require a better understanding of life on Earth. He points out that
though we know terrestrial life goes back several billion years, it becomes
increasingly difficult to detect its signs the further back one looks.

The Allan Hills meteorite -- a highly random sample from Mars that has an
unknown origin -- has "underlined some of the big problems that we face in
establishing biogenicity in old rocks," Farmer said," even on our own
planet."

Unless a sample of material is extremely well preserved, searching for signs
of organic life within it is very difficult, he said. The trick on Earth has
always been to find the few rare environments where the signatures of life
have been preserved.

Missions to Mars, which could bring back samples for study here on Earth,
need to be targeted to the places most likely to harbor signatures of life,
Farmer said.
Received on Tue 27 Feb 2001 07:45:10 PM PST