Ever since scientists learned that water once flowed on Mars, they have wondered whether life might also have flourished on the apparently now-dead planet.
In the 16 August '96 issue of Science, McKay et al report the first
identification of organic compounds in a Martian meteorite.
The authors further suggest that these compounds, in conjunction with a number of other mineralogical features observed in the rock, may be evidence of ancient Martian microorganisms.
The paper's authors are David S. McKay and Everett K. Gibson, Jr., of NASA's Johnson Space Center in Houston, TX; Kathie L. Thomas-Keprta of Lockheed Martin in Houston, TX; Hojatollah Vali of McGill University in Montreal, Quebec; Christopher S. Romanek of the University of Georgia's Savannah River Ecology Laboratory in Aiken, SC; and Simon J. Clemett, Xavier D.F. Chllier, Claude R. Maechlin, and Richard N. Zare of Stanford University in Stanford, CA.
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.
Below is some photographic evidence for this discovery.
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.
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.
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.
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.
Link to some background texts on MarsLife? in ARVAL's Image Gallery
Links to the original works at the following NASA-JPL sites:
Meteorite Yields Evidence of Primitive Life on Early Mars
The ALH 84001 Meteorite
Mars Meteorite Home Page
Links to additional works at the Lunar and Planetary Institute site:
What is ALH 84001?
Fossil Life in ALH 84001?
On 2002, David J. Barber and Edward R. D. Scott disagree with NASA on this matter:
Origin of supposedly biogenic magnetite in the Martian meteorite Allan Hills 84001
Crystals of magnetite (Fe3O4) and periclase (MgO) in Fe-Mg-Ca carbonate in the Martian meteorite Allan Hills 84001 were studied by using transmission electron microscopy to understand their origin and evaluate claims that the magnetites were made by Martian microorganisms. In magnesian carbonate, periclase occurs as aggregates of crystals (grain size ~3 nm) that are preferentially oriented with respect to the carbonate lattice. Larger periclase crystals ~50 nm in size are commonly associated with voids of similar size. Periclase clearly formed by precipitation from carbonate as a result of partial decomposition and loss of CO2. Magnetite occurs in more ferroan carbonate, and, like periclase, it is associated with voids and microfractures and the two oxides may be intermixed. Magnetite nanocrystals that are commonly euhedral and entirely embedded in carbonate are topotactically oriented with respect to the carbonate lattice, showing that they formed as solid-state precipitates. Magnetites in Fe-rich carbonate rims are not well oriented. These magnetites are generally more irregular in shape and diverse in size than the euhedral variety. All occurrences of magnetite and periclase are entirely consistent with in situ growth by solid-state diffusion as a result of carbonate decomposition during impact heating. Biogenic sources should not be invoked for any magnetites.
See Origin of supposedly biogenic magnetite in the Martian meteorite Allan Hills 84001 (David J. Barber and Edward R. D. Scott. PNAS, March 19, 2002)
Updated: August 12 '96, May 14 '13, March 15 '15
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