'Lucy' no longer the oldest human ancestor

For Darryl Granger, a little more than a decade has felt like millions of years.

In 2003, Granger estimated a hominid skeleton known as "Little Foot," found 21 years ago in a cave in South Africa, was about 4 million years old. But his method of dating the remains was widely questioned by the scientific community.

"There was quite a bit of controversy around the first age we published," said the Purdue University professor of earth, atmospheric and planetary sciences.

A new process, however, confirms with little doubt the remains are about 3.7 million years old, which is several hundred thousand years older than "Lucy," a skeleton found in Ethiopia believed to be among the oldest early ancestors to humans.

Granger published his research Wednesday on the journal Nature's website. Purdue professor Marc Caffee and scientists from universities in South Africa, France and Canada co-authored the report.

"This represents a long-standing problem that has been bugging me for years and years," Granger said in a phone interview Thursday. "But we haven't had the technology required to answer the question until just this year."

Granger said Little Foot met his demise after falling through a vertical shaft onto a pile of rocks. When he originally dated the skeleton, the process limited him to measuring the fine sands around the fossil, he said, which he estimated were 4 million years old, much older than other artifacts found in the same cave.

"People were skeptical of that," he said, "and because we dated just the fine sand, there was always the possibility that the skeleton and the large rocks had fallen into the entrance, but the fine sand had washed in from somewhere else."

Then a group of scientists dated stones near the burial site at about 2 million years old, casting more doubt on Granger's findings. But the new paper meticulously maps the cave sediments, showing "beyond doubt" that younger specimens had washed or fallen into the burial site through voids in the cave, according to a media release from the University of the Witwatersrand in Johannesburg, South Africa.

Multiple samples from the same site were measured in Purdue's PRIME lab in 2014, the release states, using a new process to more accurately separate and date aluminum and beryllium from unwanted properties in the sediment.

"The new results are going to be much more robust," Granger said, "and they're very difficult to criticize on either geologic or dating grounds."

The new research could open the door for even more ground-breaking discoveries, he noted.

"We hope that our research and our methods will lead to better dating at other sites, helping to anchor the timing of human evolution in places that remain poorly dated," he said. "This includes many South African sites as well as others around the world."