[meteorite-list] 10 Years Later, Life-On-Mars Debate Still On (ALH 84001)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Aug 7 01:06:04 2006
Message-ID: <200608070503.WAA19510_at_zagami.jpl.nasa.gov>

http://www.chron.com/disp/story.mpl/space/4096212.html

10 years later, life-on-Mars debate still on

JSC team hoping fall publication of recent research dispels doubts on
meteorite findings

By MICHAEL RAY TAYLOR
Houston Chronicle
August 5, 2006

On Aug. 7, 1996, NASA made what future generations may regard as the
greatest scientific announcement of all time.

Or not.

That day, in a press conference called by NASA headquarters in advance
of a paper in the journal Science, scientists from Johnson Space Center
made international headlines with claims they had found evidence of
primitive life on Mars.

A decade later, the loose consensus among scientists, journalists and
the general public is that the team failed to prove its extraordinary
claims.

''It must be 98 percent of the scientific community that have decided
there was no conclusive evidence of biology" in the meteorite, said
William Schopf, an expert in bacterial fossils at UCLA and one of the
most visible skeptics of the JSC team's claims.

But for those who follow the complex twists and turns of the
potato-sized rock called ALH 84001, as presented in the world's leading
scientific journals and conferences, the question of ancient Martian
life remains far from settled. Surprisingly, the only aspect of the rock
about which nearly all scientists agree is that it came from Mars and
that it is older than any known rock from Earth.

Increasingly tiny amounts of it have been sliced and sent to thousands
of researchers, who have published hundreds of studies. The JSC team
alone has produced 10 additional papers and more than 50 scientific
abstracts on the meteorite.

The rock changed the way many scientists think about life in the
universe and how to search for it. It helped change priorities at NASA
and the space agencies of other nations for exploration of the solar
system, resulting in an unprecedented six spacecraft now orbiting and
robots roving the Red Planet.

And it changed the lives of the trio of JSC scientists - David McKay,
Everett Gibson and Kathie Thomas-Keprta - who have spent 10 years
defending their controversial claim.

Using tools that didn't exist in 1996, they continue to study the
Martian meteorite, along with other meteorites from Mars, some of which
were only recently discovered. Despite widespread doubt, they remain
''more convinced than ever" they found the fossils of extraterrestrial
bacteria.

''I think there is a perception that we have been disproved," said
McKay, lead author of the 1996 Science paper. ''We need to point out,
number one, we've not been disproved, and, number two, in many cases
we've been able to show that the people who say we've been disproved are
flat wrong."

Lines of evidence

The Allan Hills, like several other ranges in Antarctica, provide a
great place to look for meteorites. Ancient ice sheets, thousands of
years old and thousands of feet thick, push against the rocky hills and
are slowly lifted to the surface, where a constant wind evaporates the ice.

Anything that's fallen on the ice in the previous 50,000 years or so
remains behind.

Until humans arrived on the scene, nothing fell there but rocks from
space. In 1984, a researcher found the Allan Hills meteorite and applied
the standard designation to the specimen - an abbreviation describing
location, year and order of discovery: ALH 84001.

For the next decade, an array of scientists examined the rock and made
some surprising discoveries: It was volcanically formed on a planet and
incredibly old, nearly as old as the solar system itself. It contained
materials rare on Earth that carried elemental fingerprints for Mars
(known since the Viking landers recorded Martian chemistry in 1976). It
had been exposed to flowing water at some point before it left Mars.

In the early 1990s, Gibson became interested in what was then a dozen or
so rocks collectively called the Martian meteorites (today there are 38
known). While examining signs of ancient water within ALH 84001, using a
powerful electron microscope new to JSC, he was the first to see what he
thought looked like biological shapes, preserved within pea-shaped
deposits called carbonate globules.

He shared his observations with colleagues McKay and Thomas-Keprta, and
as they began studying the area within the rock where the unusual shapes
were found, they gradually assembled four lines of evidence of "possible
biogenic activity."

Alone, none of these lines of evidence was strong enough to make a case
for extraterrestrial life. But with all four coming together at one tiny
point in the rock, where water had once been, they thought the four
lines of evidence were "strongly suggestive" of ancient life.

They still do.

''In the past 10 years, some very prominent researchers have supported
us," Gibson said. "They basically say that every criteria we used is a
correct interpretation of the data and does support the conclusion of
past Martian life."

'Coffin nails'

On the other hand, Gibson said, there are critics who, with every paper
or conference presentation, say, "This disproves life on Mars.

"Well, wait a minute," he said. "You have to look at what we did and
what we laid out. We said we had evidence of spatial relationships
within this rock that could be interpreted as biogenic activity on Mars.
And those lines of evidence, all four of them, still stand today."

The most publicized criticisms make sense in the abstract, Gibson said,
but cannot be at work in ALH 84001 because other, adjacent chemical
signatures make them impossible.

Thomas-Keprta said some critics have described their own studies as
''nails in the coffin" of life on Mars to the media.

''I've taken a certain amount of pleasure handing those coffin nails
back to them," she said.
      
Artificial vs. natural

Most recently, Thomas-Keprta has focused on the tiny grains of a mineral
called magnetite.

As the name implies, magnetite is magnetic. On Earth, some water and
soil bacteria secrete the crystalline mineral within their cells. The
bacteria then line up in magnetic chains like a compass needle, using
the magnetite to sense direction.

In 1996, even critics regarded the chains of magnetites within the
carbonates of ALH 84001 as the strongest of the team's four lines of
evidence.

But in a series of studies culminating in a 2002 paper, a group of
critics claimed they had created magnetites identical to those in the
Allan Hill meteorites in the laboratory by artificial means. Therefore,
they said, it was unlikely that the Martian magnetites were created by life.

The JSC team has done its own series of experiments, to be published
this fall, which they claim show the magnetites in the meteorite could
not have been formed artificially.

Among several flaws in the critics' work, Thomas-Keprta said, is the
heat required to make artificial magnetites - above 450 degrees Celsius.
The team cites studies by U.S. and German researchers that concluded the
carbonate globules within the meteorite never were subjected to heat
greater than 110 degrees Celsius.

Thomas-Keprta also has collected evidence that the critics' magnetites
were not identical in shape to those in ALH 84001, as claimed.

Other explanations

Critics have also presented nonbiological explanations for the JSC
team's other three lines of evidence: water-deposited carbonates;
organic molecules called ''polycyclic aromatic hydrocarbons"; and
squiggly shapes that resemble bacteria.

They have said that the PAHs came from Antarctic ice, not Mars, and that
the bacterialike shapes were fractured mineral surfaces or were produced
while preparing samples for the electron microscope. Biologists also
have attacked the squiggly rods - much smaller than common bacteria - as
simply too small to hold the machinery of life.

The JSC team's responses: Though as much as 80 percent of organic PAHs
in the rock did come from water flowing through Antarctic ice, a study
from the University of Arizona confirmed that at least 20 percent bear
chemical signatures from Mars. And these are concentrated in the small
areas of the rock where the JSC team claimed evidence of life.

The team also has recruited support from biological researchers who
claim to have found in nature and cultured in the lab tiny organisms
called "nanobacteria" - whose existence is as hotly debated by
microbiologists as Mars-life claims are by planetary scientists.

Jump-started science

Both sides agree that, however contentious the debate, the process
ultimately has been good for science, forcing scientists, as well as
NASA and other institutions, to ask big questions: What is life? How did
it begin? How and where can you find evidence?

Gibson points out that a whole science, ''astrobiology," or the study of
possible life on other worlds, was jump-started by their work.

''In 1996, you couldn't find a university class in astrobiology," he
said. ''Now major universities are granting doctorates in it."

Ralph Harvey of Case Western Reserve University in Cleveland, another
vocal critic, called ALH 84001 "the most-studied few grams of rock on
this planet."

''It can be thought of as a subtle recorder of the entire history of Mars."

By learning to read that history, Harvey said, scientists are
better-prepared to analyze a future Martian sample.

Schopf remains open to evidence of microbial life in Mars' ancient past
- just not in ALH 84001.

''I really believe," he said, "that we won't come to a positive
conclusion about life on Mars until we bring a sample back, and ask
every scientific question we can of it."
Received on Mon 07 Aug 2006 01:03:25 AM PDT