This image of the meteorite, seen through a scanning electron microscope, shows bumps that resemble a fossilized colony of microbacteria. Some of the rounded bumps are preserved at the top of the surface and resemble individual spherical and ovoid-shaped microbes. Image credit: NASA.

(PhysOrg.com) — In 1996, when scientists examined a meteorite from Mars previously uncovered in Antarctica, they were intrigued by what looked like microscopic fossils of ancient Martian life forms. Now, using new technology that wasn't available 13 years ago, NASA scientists have found further evidence that the materials and structures in the meteorite are likely signs of ancient life, rather than the results of inorganic processes.

 

ALH84001 History

Scientists estimate that the , called Allan Hills 84001 (ALH84001), formed on about 4.5 billion years ago, making it one of the oldest known objects in the solar system. Because the meteorite contains microscopic carbonate disks that are about 4 billion years old, scientists have previously hypothesized that the meteorite interacted with water that may have existed on Mars at this time.

Much later, about 15 million years ago, a larger meteorite likely struck Mars and ejected ALH84001 into space. After spending most of that time traveling throughout the , the meteorite landed on Earth about 13,000 years ago. Then, in 1984, a team of US scientists discovered it in Antarctica. The meteorite finally made news headlines in 1996, when NASA scientist David McKay and others peered at the rock under a and saw what appeared to be nanoscale fossils of bacteria-like life forms.

Bacterial or Thermal Origin?

Now, McKay, along with Kathie Thomas-Keprta, Everett Gibson, Simon Clemett, and Susan Wentworth, all of NASA's Johnson Space Center, have revisited the original hypothesis with new observations of the meteorite. The study is published in a recent issue of the journal Geochimica et Cosmochimica Acta.

In the new study, the scientists…

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