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 was reported in the Aug. 16, 1996 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.
August 6, 1996 NASA Press Release 96-159
Statement from Daniel S. Goldin, NASA Administrator
"NASA has made a startling discovery that points to the possibility that a primitive form of microscopic life may have existed on Mars more than three billion years ago. The research is based on a sophisticated examination of an ancient Martian meteorite that landed on Earth some 13,000 years ago.
The evidence is exciting, even compelling, but not conclusive. It is a discovery that demands further scientific investigation. NASA is ready to assist the process of rigorous scientific investigation and lively scientific debate that will follow this discovery.
I want everyone to understand that we are not talking about little green men. These are extremely small, single- cell structures that somewhat resemble bacteria on Earth. There is no evidence or suggestion that any higher life form ever existed on Mars.
The NASA scientists and researchers who made this discovery will be available at a news conference tomorrow to discuss their findings. They will outline the step-by-step 'detective story' that explains how the meteorite arrived here from Mars, and how they set about looking for evidence of long-ago life in this ancient rock. They will also release some fascinating images documenting their research."
August 7, 1996 NASA Press Release 96-160
Meteorite Yields Evidence of Primitive Life on 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.
S94-032549 This 4.5 billion-year-old rock, labeled meteorite ALH84001, is believed to have once been a part of Mars and to contain fossil evidence that primitive life may have existed on Mars more than 3.6 billion years ago. The rock is a portion of a meteorite that was dislodged from Mars by a huge impact about 16 million years ago and that fell to Earth in Antarctica 13,000 years ago. The meteorite was found in Allan Hills ice field, Antarctica, by an annual expedition of the National Science Foundation's Antarctic Meteorite Program in 1984. It is preserved for study at the Johnson Space Center's Meteorite Processing Laboratory in Houston.
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.
S96-12301 In the center of this electron microscope image of a small chip from a meteorite are several tiny structures that are possible microscopic fossils of primitive, bacteria-like organisms that may have lived on Mars more than 3.6 billion years ago. A two-year investigation by a NASA research team found organic molecules, mineral features characteristic of biological activity and possible microscopic fossils such as these inside of an ancient Martian rock that fell to Earth as a meteorite. The largest possible fossils are less than 1/100th the diameter of a human hair in size while most are ten times smaller.
S96-12301 This electron microscope image is a close-up of the center part of photo number S96-12301. While the exact nature of these tube-like structures is not known, one interpretation is that they may be microscopic fossils of primitive, bacteria-like organisms that may have lived on Mars more than 3.6 billion years ago.
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.
S96-12297 This electron microscope image shows egg-shaped structures, some of which may be possible microscopic fossils of Martian origin as discussed by NASA research published in the Aug. 16, 1996, issue of the journal Science.
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.
S96-12300 This electron microscope image shows tubular structures of likely Martian origin. These structures are very similar in size and shape to extremely tiny microfossils found in some Earth rocks. This photograph is part of a report by a NASA research team published in the Aug. 16, 1996, issue of the journal Science.
S96-12298 This electron microscope image shows extremely tiny tubular structures that are possible microscopic fossils of bacteria-like organisms that may have lived on Mars more than 3.6 billion years ago. The fossil-like structures were found in carbonate minerals formed along pre-existing fractures in the meteorite in a fashion similar to the way fossils occur in limestone on Earth, although on a microscopic scale.
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.
S96-12609 This high-resolution scanning electron microscope image shows an unusual tube-like structural form that is less than 1/100th the width of a human hair in size found in meteorite ALH84001, a meteorite believed to be of Martian origin. Although this structure is not part of the research published in the Aug. 16 issue of the journal Science, it is located in a similar carbonate glob in the meteorite. This structure will be the subject of future investigations that could confirm whether or not it is fossil evidence of primitive life on Mars 3.6 billion years ago.
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.
S95-00690 This photograph shows orange-colored carbonate mineral globules found in a meteorite, called ALH84001, believed to have once been a part of Mars. These carbonate minerals in the meteorite are believed to have been formed on Mars more than 3.6 billion years ago. Their structure and chemistry suggest that they may have been formed with the assistance of primitive, bacteria-like living organisms.
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.
The Martian Meteorites
The Mars Missions
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