Researchers say a skeleton unearthed decades ago in the sand dunes of Lake Mungo, Australia, may be tens of thousands of years older than once assumed. The findings, which appear in the June issue of the Journal of Human Evolution, not only push back the arrival of people in Australia but also call into question some theories about how modern humans spread around the globe.
The skeleton, called Mungo 3, was uncovered in 1974. Archaeologist Alan Thorne, from Australian National University (ANU) in Canberra, determined that the body had been ceremonially buried in a grave, with red ocher scattered over it and its fingers intertwined around its penis. Carbon-14 dating initially put its age at 28,000 to 32,000 years old, but refinements in the technique in the 1980s led to an age of at least 38,000 years--and possibly older, because the 14C technique can't reach beyond 40,000 years. Newer techniques can reach further back in time, but some researchers are skeptical about them because they are tricky to use (Science, 10 October 1997, p. 220 ).
In a new attempt to date Mungo 3, Thorne and his colleagues decided to use a combination of three techniques. One, OSL, dates the sediments surrounding the fossil by counting the electrons that natural radiation knocks into defects in a mineral's crystal structure. The other two date the fossil itself, either by counting electrons trapped in the crystal structure of bone or tooth or by measuring how much of the uranium in the sample has decayed into its daughter elements. The three methods gave pretty much the same result: 61,000 ± 2000 years from OSL, and 62,000 ± 6000 years from the two other methods.
If true, the results mean that humans arrived in Australia at least 60,000 years ago. And that would have profound implications for human history. Many researchers maintain that all modern humans descend from a single population of Africans, who brought with them art, ritual burials, and other signs of cognitive sophistication as they spread around the world. The oldest solid evidence for this "human revolution" in Africa is 50,000 years old, and 40,000 years old in Europe (Science, 23 November 1998, p. 1451 ). But the ceremonial burial of Mungo 3 (and the boat-building skills required to reach Australia) point to such sophistication at a much earlier date. If the date is real, says Stanford University's Richard Klein, "it would mean either that there was a separate evolution of modern humans and modern human behavior in the Far East, or that modern humans emerging from Africa somehow managed to reach the Far East at least 20,000 years before they reached the Far West."