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By Sean Henahan, Access Excellence

HOUSTON (August 7, 1996) Analysis of a small meteorite that landed on Antarctica some 15 million years ago has sparked what may be the greatest scientific discovery ever, possible evidence of life on Mars.

Graphic: False-color backscatter electron (BSE) image of fractured surface of a chip from ALH84001 meteorite showing distribution of the carbonate globules.

A team of researchers at NASA's Johnson Space Center have identified organic compounds on the Martian meteorite, the first ever such discovery. Details of the research will appear in the August 16, 1996 issue of the journal Science. The embargo was lifted after the news began to leak out. NASA held a press conference today describing the findings.

"Scientists have 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," announced NASA administrator Daniel Goldin.

The researchers looked for complex, carbon-based molecules and other mineralogical and textural indications of past life within the pore space and fractures of the meteorite known as Allan Hills 84001 (ALH84001), one of only a dozen meteorites identified as having come from Mars. ALH84001 is the oldest of these, having crystallized from molten rock about 4.5 billion years ago, early in the planet's evolution. It is the only Martian meteorite to contain significant carbonate minerals.

The meteorite was flung across space following a major asteroid impact some 15 million years ago. The scientists believe it landed in an ice field in Antarctica about 13,000 years ago. The meteorite was found in 1984 but only recently identified as coming from Mars.

The researchers were amazed to discover the existence of polycyclic aromatic hydrocarbons in fractures in the meteorite. resulting primarily from impacts that occurred while the rock was on Mars. The concentration and location of the PAH's led the scientists to conclude that they are the remnants of bacterial life forms. The scientists conducted exhaustive precautionary procedures to confirm that the samples had not been contaminated on Earth.

PAH's can form one of two ways: non-biologically, during early star formation; or biologically, through the activity of bacteria or other living organisms, or their degradation (fossilization). On Earth, PAHs are abundant as fossil molecules in ancient sedimentary rocks, coal and petroleum, the result of chemical changes that occurred to the remains of dead marine plankton and early plant life. They also occur during partial combustion, such as when a candle burns or food is grilled.

The researchers examined the chemistry, mineralogy, and texture of carbonates associated with PAH's in the Martian meteorite. Under the transmission electron microscope, the carbonate globules were seen to contain fine-grained magnetite and iron-sulfide particles. From these and other analyses, the team developed a list of observations about the carbonates and PAH's that, taken individually, could be explained by non-biological means. However, as they note in the Science article, "when considered collectively...we conclude that [these phenomena] are evidence for primitive life on early Mars."

Some of their key observations include:

  • The highest concentrations of PAHs were found associated with the carbonates.

  • The carbonates formed within the rock fissures, about 3.6 billion years ago, and are younger than the rock itself.

  • The magnetite and iron-sulfide particles inside the carbonate globules are chemically, structurally and morphologically similar to magnetosome particles produced by bacteria on Earth.

  • High-resolution scanning electron microscopy revealed on the surface of the carbonates small (100 nanometers) ovoids and elongated features. Similar textures have been found on the surface of calcite concretions grown from Pleistocene groundwater in southern Italy, which have been interpreted as representing nanobacteria.

  • Some earlier reports had suggested that the temperature at which the ALH84001 carbonates formed was as high as 700�C -- much too hot for any kind of life. However, the isotopic composition of the carbonates, and the new data on the magnetite and iron-sulfide particles, imply a temperature range of 0� to 80�C, cool enough for life.

  • The magnetite -- a mineral which contains some ferric (Fe3+) iron, perhaps indicating formation by oxidation (the addition of oxygen) -- and iron sulfide -- a mineral that can be formed by reduction (the loss of oxygen) -- were found in close proximity in the Martian meteorite. On Earth, closely associated mineralogical features involving both oxidation and reduction are characteristic of biological activity.

The new discovery could not have happened at a better time for NASA, which has been a subject of budget cuts recently. NASA will be launching an unmanned spacecraft to Mars this Novemeber called the Mars Global Surveyor. Another mission, the Mars Pathfinder spacecraft will launch in December. NASA has established an innovative program, "Live From Mars" specifically designed for science teachers and their students.

"I am determined that the American space program will put its full intellectual power and technological prowess behind the search for further evidence of life on Mars. If this discovery is confirmed it will surely be one of the most stunning insights into our universe that science has ever uncovered. Its implications are as far-reaching and awe-inspiring as can be imagined,'' said President Clinton in a statement.

Clinton has directed Vice President Al Gore to convene a bipartisan space summit' at the White House later this year to discuss the future of America's space program including how to pursue scientific questions raised by the Mars meteorite. The new findings are certain to shake up the research community. Some researchers are already suggesting it may be possible to extrapolate the findings to outside of our solar system:

"It makes it very promising there may be life in other solar systems. What it really does show is the formation of life on a planet can take place rather easily,'' noted biochemist Stanley Miller at the University of California at San Diego. Miller, who specializes in the study of the origins of life is most well known for his 'creation of life in the test tube' experiments.

Related information on the Internet

Science Article: Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001, David S. McKay et al.

More Mars Meteor Pictures

"Live From Mars"

NASA web site

Johnson Space Center

Informa tion on Shergotty-Nakhla-Chassigny (SNC) Meteorites

Clues to The Origins of Life

Science Updates Index

What's News Index


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