[meteorite-list] Mars Meteorite May Or May Not Show Signs Of Life; Four-Year Debate Continues
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:44 2004
Mars meteorite may or may not show signs of life, but four-year debate over
it definitely still does
By Alexandra Witze
The Dallas Morning News
March 26, 2001
HOUSTON - To some scientists, the movie that best describes the hunt for
extraterrestrial life would be Invaders From Mars.
Other scientists might prefer Night of the Living Dead.
For 4 1/2 years, the protagonist has been a particular Martian meteorite; the
drama, whether it holds evidence that life once existed on the Red Planet.
New work, reported within the past month, either strengthens or weakens that
case - depending on the point of view.
Supporters say the evidence for life on Mars is stronger than ever. But
critics, who come in far greater numbers, say that the arguments have taken
on a zombielike quality, refusing to die.
This month, at a planetary science meeting in Houston, the two sides squared
off in what has become a yearly confrontation. The object of all this
attention: an unassuming rock called ALH84001, after the Allan Hills region
of Antarctica where it was discovered in 1984 after traveling there from
Despite the bitterness of the scientific debate, one good thing has come
from studying ALH84001, says Yale University geologist James Greenwood. "It
has forced us," he says, "to focus on whether there was life on Mars and how
we might answer that question."
After all, NASA's entire Mars program - a decadelong sequence of robotic
missions culminating in a full-fledged search for life - implicitly assumes
that organisms once existed there. By 2011, NASA hopes to launch a
spacecraft that will, for the first time, pick up Mars rocks and return them
to Earth. And only if that probe chooses the right rock - one full of
fossils - will questions about life on Mars be resolved, some scientists
The debate's latest salvos were fired in two papers published recently in
the Proceedings of the National Academy of Sciences. Two groups of
scientists, including the original life-on-Mars team from NASA, argue that
crystals of the mineral magnetite inside the meteorite strongly resemble
magnetite produced by earthly bacteria. By analogy, the researchers say, the
Martian crystals must also have been formed by living organisms, perhaps
billions of years ago when the rock itself formed.
But another scientific team, also based at NASA's Johnson Space Center, has
created magnetite crystals in the laboratory that look just like those
inside ALH84001 - with no life forms involved.
Such contradictory results leave even the meteorite experts exhausted, as
well as skeptical that the controversy will ever end.
The pro-Mars life contingent has gained a valuable ally in Imre Friedmann, a
Florida State University biologist who has studied bacteria that thrive
inside Antarctic rocks. Such bacteria, Dr. Friedmann thinks, may resemble
life forms - if any ever existed - on Mars in the past.
In his recent paper, Dr. Friedmann describes finding chains of magnetite
crystals inside ALH84001. On Earth, these chains - which, when seen through
a microscope, resemble pearl necklaces - are strung together naturally by
bacteria, which use the magnetite to navigate with Earth's magnetic field.
Scientists had looked for these chains in the Mars meteorite before, but
without luck because the acid used to prepare the rock for study caused the
chains to break up.
But using a new technique, Dr. Friedmann discovered chains, ranging from
four to 13 crystals long, inside chips of the meteorite. The crystals share
the same size and shape and are oriented as they would be had bacteria
formed them, Dr. Friedmann says.
"All the facts cannot be explained any other way than by biology," he says.
Because there are so many magnetite chains inside the meteorite, Dr.
Friedmann thinks they are remnants of dead bacteria that washed into the
rock as it lay on the Martian surface.
Still, he acknowledges that not every meteorite expert agrees with him.
"I wouldn't describe it as a smashing success," he said at the meeting,
displaying a slide covered with critical comments.
After Dr. Friedmann's talk, Allan Treiman, of the Lunar and Planetary
Institute in Houston, said: "I don't believe your chains. I think you're
fooling yourself - you're connecting dots in your mind."
John Bradley, a microscope expert from Georgia, added, "Let me summarize: I
think it's a bunch of bull." He thinks the chains may be an illusion,
created by looking through the microscope, or perhaps leftovers from the
breakdown of bigger magnetite crystals.
But a second new study, also on the magnetite crystals within ALH84001,
likewise argues the case for life on Mars. In this work, the original NASA
team reported finding specially shaped crystals inside the meteorite, which
they say can be produced only by living organisms.
Magnetite crystals inside rocks normally assume an octahedral shape,
resembling two pyramids stuck base to base. But bacteria can produce
magnetite crystals of a funnier shape - a modified one with six hexagonal
faces and eight octahedral faces, which the NASA team calls the "truncated
Bacteria make their magnetite crystals longer in order to improve the
crystals' ability to detect Earth's magnetic poles.
"The cell wants to produce the best magnet it can," says team leader Kathie
Thomas-Keprta, an astrobiologist at NASA's Johnson Space Center in Houston.
The magnetite crystals act as tiny compasses, which the bacteria use to
navigate toward food and energy sources.
New microscope images of ALH84001 reveal what appears to be truncated
hexa-octahedral crystals similar to those seen in earthly bacteria, Dr.
Thomas-Keprta reported at the meeting.
"We believe we're seeing the same thing in the Allan Hills meteorite," she
About one-quarter of all the magnetite crystals studied in the meteorite
display this unusual geometry. The most likely explanation is that Martian
bacteria created the meteorite's magnetite, Dr. Thomas-Keprta says.
At the same time, another NASA-led group has found evidence that contradicts
Elsewhere at Johnson Space Center, Douglas Ming and colleagues have created
magnetite crystals that appear to have a similar geometry - without the help
of living organisms. Reporting in the current issue of American
Mineralogist, the scientists describe a series of chemical reactions in
which iron-rich carbonate minerals decompose into magnetite crystals that
resemble those in ALH84001.
Other characteristics of the meteorite, once claimed to be evidence of life,
can also be explained through nonliving processes, Dr. Ming's team writes.
In response, Dr. Thomas- Keprta says that Dr. Ming's group can't be sure it
made magnetite with the right crystal geometry. The lab crystals were
photographed in two dimensions; a third dimension could hide a different
shape that would contradict the paper's conclusion, she argues.
"We don't have a good handle on what they're seeing," she says.
Yet other studies have dismantled key parts of the original arguments for
evidence of life, says Dr. Treiman. Study after study over the past four
years, he says, has shown that features in the meteorite could be as easily
formed by nonliving processes as by living ones. And work by Andrew Steele
of the University of Portsmouth in England has shown that most meteorites
are riddled with fragments of earthly bacteria - suggesting that ALH84001
might have been heavily contaminated.
Even if life forms did exist in the meteorite, they might not be
recognizable today, says Frances Westall of the Lunar and Planetary
Institute. She has studied known fossils on Earth, 3.45 billion years old,
that are barely recognizable as once-living creatures, even though
scientists know they are proof of ancient life.
If a Mars rock "happens to contain fossils of badly degraded bacteria," she
asks, "how will we recognize them?"
So a mission to retrieve rocks from Mars may not even resolve the question,
scientists say. And life on Mars may have to remain in the domain of science
Received on Thu 29 Mar 2001 12:36:50 PM PST