OLD SOLES?

Evidence of really, really old humans -- or nothing at all? This week's Nature mag tries to suss out the answer:

Alleged footprints of early Americans found in volcanic rock in Mexico are either extremely old - more than 1 million years older than other evidence of human presence in the Western Hemisphere - or not footprints at all, according to a new analysis published this week in Nature.

The study was conducted by geologists at the Berkeley Geochronology Center and the University of California, Berkeley, as part of an investigative team of geologists and anthropologists from the United States and Mexico.

Earlier this year, researchers in England touted these "footprints" as definitive proof that humans were in the Americas much earlier than 11,000 years ago, which is the accepted date for the arrival of humans across a northern land-bridge from Asia.

These scientists, led by geologist Silvia Gonzalez of Liverpool's John Moores University, dated the volcanic rock at 40,000 years old. They hypothesized that early hunters walked across ash freshly deposited near a lake by volcanoes that are still active in the area around Puebla, Mexico. The so-called footprints, subsequently covered by more ash and inundated by lake waters, eventually turned to rock.

But Paul Renne, director of the Berkeley Geochronology Center and an adjunct professor of earth and planetary science at UC Berkeley, and his colleagues in Mexico and at Texas A&M University report in the Dec. 1 issue of Nature a new age for the rock: about 1.3 million years.

"You're really only left with two possibilities," Renne said. "One is that they are really old hominids - shockingly old - or they're not footprints."

Probably nothing at all. Still a fascinating read.