Fossils from Mars: point, counterpoint.

The debate goes on. Researchers haven't stopped arguing about whether the Martian meteorite ALH84001 contains fossils of primitive life. In the Dec. 4, 1997 Nature, two groups--scientists on the discovery team and members of a team that has criticized their findings--duke it out.

For more than a year, the naysayers have maintained that wormlike features found within the Mars rock are not fossils of tiny bacteria (SN: 12/14/96, p. 380). However, these critics did not use the same electron microscopy technique to study the rock as the researchers who announced the initial findings.

Now they have, and they contend that the purported fossils are merely the fractured surfaces of pyroxene and carbonate crystals. These artifacts have no biological origin, assert John P. Bradley of MVA in Norcross, Ga., and the Georgia Institute of Technology in Atlanta, Ralph P. Harvey of Case Western Reserve University in Cleveland, and Harry Y. McSween Jr. of the University of Tennessee in Knoxville.

Members of the discovery team agree that the microstructures examined by Bradley and his colleagues are not fossils. Indeed, they maintain that they long ago discounted similar artifacts in their own samples.

"I don't know how else to put this, but we're not stupid," says Kathie Thomas-Keprta, a Lockheed Martin researcher based at NASA's Johnson Space Center in Houston.

She and her collaborators note that the features which might represent tiny fossils occur in greater numbers, are significantly larger, and display a wider variety of orientations than the tiny crystals do. Moreover, they add, some of the possible fossils have an ovoid shape rather than the wormlike appearance of the disputed features.