“For many years, the presence of the specific kind of nanomagnetite formed by magnetotactic bacteria on Earth have been completely accepted as a biosignature when found in any Earth sediment or rock,” Thomas-Keprta said, noting that these magnetite have very specific properties.
“When we first documented these specific properties in the ALH84001 carbonates, the only alternate non-biologic hypothesis that was commonly accepted as viable was the thermal decomposition of iron-bearing carbonate,” she said. “Now that we have completely falsified this hypothesis with this latest paper, we are still left with the specific properties of the ALH84001 magnetite that, if found on Earth, would be a robust biosignature indicating production by bacteria.
“We also point to the many discoveries since our original paper showing supporting evidence such as an early strong magnetic field on Mars (necessary for the development of magnetotactic bacteria); the presence of near surface water at many locations on current-day Mars; the presence of possible oceans, major drainage channels, and other features associated with an early wet Mars; and the recent evidence for variable releases of methane into the Martian atmosphere. . . . We do not believe it is too incautious to restate our original hypothesis that such magnetites constitute strong evidence of early life on Mars.”
