Ronald Clarke, a professor in the Evolutionary Studies Institute at the University of the Witwatersrand who discovered the Little Foot skeleton, said the fossil represents Australopithecus prometheus, a species very different from its contemporary, Australopithecus afarensis, and with more similarities to the Paranthropus lineage."It demonstrates that the later hominids, for example, Australopithecus africanus and Paranthropus did not all have to have derived from Australopithecus afarensis," he said.Previous dates ranged from 2 million to 4 million years old, with an estimate of 3 million years old preferred by paleontologists familiar with the site, said Darryl Granger, a professor of earth, atmospheric and planetary sciences at Purdue, who in collaboration with Ryan Gibbon, a former postdoctoral researcher, led the team and performed the dating.
Samples that have been compromised, due to reburial or natural movement of sediment within a site, fall above or below the line can be tossed out of the analysis, Granger said.
Because of their very slow rate of decay, these particular radioisotopes allow dating to reach back millions of years, much further in history than the more commonly known carbon-14 dating that can only stretch back about 50,000 years, he said.
Only a small amount of the radioisotopes remain in the quartz after millions of years, and it can only be measured by the ultrasensitive analysis of accelerator mass spectrometry.
"If we had only one sample and that rock happened to have been buried, then re-exposed and buried again, the date would be off because the amount of radioisotopes would have increased during its second exposure," he said.
"With this method we can tell if that has happened or if the sample has remained undisturbed since burial with the fossil.