[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Meteorite Yields Evidence of Primitive Life on Early Mars



Donald L. Savage
Headquarters, Washington, DC             August 7, 1996
(Phone:  202/358-1727)

James Hartsfield
Johnson Space Center, Houston, TX
(Phone:  713/483-5111)

David Salisbury
Stanford University, Palo Alto, CA
(Phone:  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 (JSC), Houston, TX, and at Stanford University, Palo 
Alto, CA, 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 August 16 issue of the journal Science, 
presenting the investigation to the scientific community at 
large for further study.

       The two-year investigation was co-led by JSC planetary scientists 
Dr. David McKay, Dr. Everett Gibson and Kathie Thomas-Keprta 
of Lockheed-Martin, 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.

       Since 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 
also may 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, 16 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 researchers 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 1/100 
the diameter of a human hair, and most are about 1/1000 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 similar 
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 Meteorite 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 dual 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 addition, 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 can be 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 similar 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. 

     Additional information may be obtained at 1 p.m. EDT via 
the Internet at

http://www.jsc.nasa.gov/pao/flash/