August 7, 1996

James Hartsfield
Johnson Space Center
(713) 483-5111

David Salsbury
Stanford University
(415) 723-2558

Release: 96-160

METEORITE YIELDS EVIDENCE OF PRIMITIVE LIFE ON EARLY MARS


A NASA research team of scientists at the Johnson Space Center and at Stanford
University has found evidence that strongly suggests primitive life may have existed
on Mars more than 3.6 billion years ago.

The NASA-funded team found the first organic molecules thought to be of Martian
origin; several mineral features characteristic of biological activity; and possible
microscopic fossils of primitive, bacteria-like organisms inside of an ancient Martian
rock that fell to Earth as a meteorite. This array of indirect evidence of past life will
be reported in the Aug. 16 issue of the journal Science, presenting the investigation
to the scientific community at large to reach a future consensus that will either
confirm or deny the team's conclusion.

The two-year investigation was co-led by planetary scientists Dr. David McKay,
Dr. Everett Gibson and Kathie Thomas-Keprta of Lockheed-Martin, all from JSC,
with the major collaboration of a Stanford team headed by Professor of Chemistry
Dr. Richard Zare, as well as six other NASA and university research partners.

"There is not any one finding that leads us to believe that this is evidence of past life
on Mars. Rather, it is a combination of many things that we have found," McKay
said. "They include Stanford's detection of an apparently unique pattern of organic
molecules, carbon compounds that are the basis of life. We also found several
unusual mineral phases that are known products of primitive microscopic organisms
on Earth. Structures that could be microsopic fossils seem to support all of this. The
relationship of all of these things in terms of location – within a few hundred
thousandths of an inch of one another – is the most compelling evidence."

"It is very difficult to prove life existed 3.6 billion years ago on Earth, let alone on
Mars," Zare said. "The existing standard of proof, which we think we have met,
includes having an accurately dated sample that contains native microfossils,
mineralogical features characteristic of life, and evidence of complex organic
chemistry."

"For two years, we have applied state-of-the-art technology to perform these
analyses, and we believe we have found quite reasonable evidence of past life on
Mars," Gibson added. "We don't claim that we have conclusively proven it. We are
putting this evidence out to the scientific community for other investigators to verify,
enhance, attack -- disprove if they can -- as part of the scientific process. Then,
within a year or two, we hope to resolve the question one way or the other."

"What we have found to be the most reasonable interpretation is of such radical
nature that it will only be accepted or rejected after other groups either confirm our
findings or overturn them," McKay added.

The igneous rock in the 4.2-pound, potato-sized meteorite has been age-dated to
about 4.5 billion years, the period when the planet Mars formed. The rock is
believed to have originated underneath the Martian surface and to have been
extensively fractured by impacts as meteorites bombarded the planets in the early
inner solar system. Between 3.6 billion and 4 billion years ago, a time when it is
generally thought that the planet was warmer and wetter, water is believed to have
penetrated fractures in the subsurface rock, possibly forming an underground water
system.

Because the water was saturated with carbon dioxide from the Martian atmosphere,
carbonate minerals were deposited in the fractures. The team's findings indicate
living organisms may also have assisted in the formation of the carbonate, and some
remains of the microscopic organisms may have become fossilized, in a fashion
similar to the formation of fossils in limestone on Earth. Then, 15 million years ago, a
huge comet or asteroid struck Mars, ejecting a piece of the rock from its subsurface
location with enough force to escape the planet. For millions of years, the chunk of
rock floated through space. It encountered Earth's atmosphere 13,000 years ago
and fell in Antarctica as a meteorite.

It is in the tiny globs of carbonate that the researchers found a number of features
that can be interpreted as suggesting past life. Stanford found easily detectable
amounts of organic molecules called polycyclic aromatic hydrocarbons (PAHs)
concentrated in the vicinity of the carbonate. Researchers at JSC found mineral
compounds commonly associated with microscopic organisms and the possible
microscopic fossil structures.

The largest of the possible fossils are less than 1/100th the diameter of a human hair,
and most are about 1/1000th the diameter of a human hair – small enough that it
would take about a thousand laid end-to-end to span the dot at the end of this
sentence. Some are egg-shaped while others are tubular. In appearance and size,
the structures are strikingly similiar to microscopic fossils of the tiniest bacteria found
on Earth.

The meteorite, called ALH84001, was found in 1984 in Allan Hills ice field,
Antarctica, by an annual expedition of the National Science Foundation's Antarctic
Meterorite Program. It was preserved for study in JSC's Meteorite Processing
Laboratory and its possible Martian origin was not recognized until 1993. It is one
of only 12 meteorites identified so far that match the unique Martian chemistry
measured by the Viking spacecraft that landed on Mars in 1976. ALH84001 is by
far the oldest of the 12 Martian meteorites, more than three times as old as any
other.

Many of the team's findings were made possible only because of very recent
technological advances in high-resolution scanning electron microscopy and laser
mass spectrometry. Only a few years ago, many of the features that they report
were undetectable. Although past studies of this meteorite and others of Martian
origin failed to detect evidence of past life, they were generally performed using
lower levels of magnification, without the benefit of the technology used in this
research. The recent discovery of extremely small bacteria on Earth, called
nanobacteria, prompted the team to perform this work at a much finer scale than
past efforts.

The nine authors of the Science report include McKay, Gibson and Thomas-Keprta
of JSC; Christopher Romanek, formerly a National Research Council post-doctoral
fellow at JSC who is now a staff scientist at the Savannah River Ecology Laboratory
at the University of Georgia; Hojatollah Vali, a National Research Council
post-doctoral fellow at JSC and a staff scientist at McGill University, Montreal,
Quebec, Canada; and Zare, graduate students Simon J. Clemett and Claude R.
Maechling and post-doctoral student Xavier Chillier of the Stanford University
Department of Chemistry.

The team of researchers includes a wide variety of expertise, including microbiology,
mineralogy, analytical techniques, geochemistry and organic chemistry, and the
analysis crossed all of these disciplines. Further details on the findings presented in
the Science article include:

Researchers at Stanford University used a laser mass spectrometer -- the most
sensitive instrument of its type in the world – to look for the presence of the
common family of organic molecules called PAHs. When microorganisms die, the
complex organic molecules that they contain frequently degrade into PAHs. PAHs
are often associated with ancient sedimentary rocks, coals and petroleum on Earth
and can be common air pollutants. Not only did the scientists find PAHs in easily
detectable amounts in ALH84001, but they found that these molecules were
concentrated in the vicinity of the carbonate globules. This finding appears consistent
with the proposition that they are a result of the fossilization process. In addtion, the
unique composition of the meteorite's PAHs is consistent with what the scientists
expect from the fossilization of very primitive microorganisms. On Earth, PAHs
virtually always occur in thousands of forms, but, in the meteorite, they are
dominated by only about a half-dozen different compounds. The simplicity of this
mixture, combined with the lack of light-weight PAHs like napthalene, also differs
substantially from that of PAHs previously measured in non-Martian meteorites.

The team found unusual compounds -- iron sulfides and magnetite -- that are
commonly produced by anaerobic bacteria and other microscopic organisms on
Earth. The compounds were found in locations directly associated with the
fossil-like structures and carbonate globules in the meteorite. Extreme conditions --
conditions very unlikely to have been encountered by the meteorite -- would have
been required to produce these compounds in close proximity to one another if life
were not involved. The carbonate also contained tiny grains of magnetite that are
almost identical to magnetic fossil remnants often left by certain bacteria found on
Earth. Other minerals commonly associated with biological activity on Earth were
found in the carbonate as well.

The formation of the carbonate or fossils by living organisms while the meteorite was
in the Antarctic was deemed unlikely for several reasons. The carbonate was age
dated using a parent-daughter isotope method and found to be 3.6 billion years old,
and the organic molecules were first detected well within the ancient carbonate. In
addition, the team analyzed representative samples of other meteorites from
Antarctica and found no evidence of fossil-like structures, organic molecules or
possible biologically produced compounds and minerals similiar to those in the
ALH84001 meteorite. The composition and location of PAHs organic molecules
found in the meteorite also appeared to confirm that the possible evidence of life
was extraterrestrial. No PAHs were found in the meteorite's exterior crust, but the
concentration of PAHs increased in the meteorite's interior to levels higher than ever
found in Antarctica. Higher concentrations of PAHs would have likely been found
on the exterior of the meteorite, decreasing toward the interior, if the organic
molecules are the result of contamination of the meteorite on Earth.

--end--