Giant Ginkgo

In the latest study of a 4.5 billion-year-old Martian meteorite, researchers have presented new evidence confirming that 25 percent of the magnetic material in the meteorite was produced by ancient bacteria on Mars. These latest results were published in the journal Applied and Environmental Microbiology.

The researchers used six physical properties they refer to as the Magnetite Assay for Biogenicity (MAB) to compare all the magnetic material found in the ancient meteorite -- using the MAB as a biosignature. A biosignature is a physical and/or chemical marker of life that does not occur through random processes or human intervention.

"No non-biologic magnetite population, whether produced by nature or in the laboratory, has ever met the MAB criteria," said Kathie Thomas-Keprta, an astrobiologist at NASA's Johnson Space Center (JSC) in Houston and the lead researcher on the study. "This means that one-quarter of the magnetite crystals embedded in the carbonates in Martian meteorite ALH84001 require the intervention of biology to explain their presence."

Magnetotactic bacteria, which occur in aquatic habitats on Earth, arrange magnetite crystals in chains within their cells to make compasses, which help the bacteria locate sources of food and energy. Magnetite (Fe3O4) is produced inorganically on Earth, but the magnetite crystals produced by magnetotactic bacteria are very different -- they are chemically pure and defect-free, with distinct sizes and shapes.