Fossilized human ancestor much older than previously thought.

2003 MAY 19 - (NewsRx.com & NewsRx.net) -- In a finding that could shed light on the earliest origins of mankind, fossil remains found in South Africa of an ancestral human species have proven far older than expected when evaluated by a Purdue University research team.

Darryl Granger and Marc Caffee have determined the age of a fossilized skeleton thought to be an Australopithecus, a genus of African hominids from which humanity is thought to have developed, by measuring the radioactivity of the cave sediments in which the skeleton was buried millions of years ago. Their measurement technique, generally used to estimate the age of geological formations such as glaciated valleys and river terraces, has never before been used to date biological fossils.

"By dating the sediments surrounding the fossil skeleton, we have determined that this species reached southern Africa approximately 4 million years ago," said Granger, associate professor of earth and atmospheric sciences in Purdue's School of Science. "If the skeleton is indeed an Australopithecus, as we believe, the findings could mean that these hominids were present in the area far earlier than is generally accepted."

The research was published in the April 25, 2003, issue of Science.

Tracing the development and spread of the hominid species that may have been mankind's ancestor is an arduous process, and it is difficult to determine what happened because precisely dated fossil records are hard to come by. Many such fossils have been found in eastern Africa's Rift Valley, a region that was geologically active when Australopithecus walked the Earth. The abundance of lake sediments and volcanic ash that often surrounds Rift Valley hominid fossils provide good clues as to their age. But there is no such luck with similar fossils from South Africa, a region that also is rich in hominid remains but lacks the definitive geological clues that are present in the Rift Valley.

T.C. Partridge and R.J. Clarke, researchers from the University of the Witwatersrand in South Africa, were thus confronted with a mixed blessing when, in 1997, they discovered a nearly complete skeleton of what appeared to be an Australopithecus buried in the sediments on the floor of the Sterkfontein cave in central South Africa. The fossil was well preserved, but its age was uncertain. It was more than 2 million years old, but how much more? The answer to that question would affect theories of how and when Australopithecus spread through Africa.

"Their initial estimate of 3.3 million years provoked a lot of controversy," Granger said. "Few thought that Australopithecus had traveled so far so long ago, and scientists wanted more proof. If the estimate was accurate, it might require a rethinking of human prehistory."