The popular “Out of Africa” theory states that Homo sapiens evolved in the Rift Valley 170,000 years ago and then migrated around the world 50,000 years ago, displacing Neanderthals and other hominid relatives. This theory was challenged in 1999 when researchers from the Australian National University claimed that Australia’s oldest skeleton, dubbed ‘Mungo Man’, was 62,000 years old–much older than had been previoudly thought. Since many palaeontologists believe that early humans could not have spread quickly enough to arrive in Australia before 50,000 years ago, this much earlier date suggested that modern humans had evolved independently in Australia, as well as in Africa. Mungo Man’s age was estimated by analyzing how much uranium had decayed in a sample from the skeleton. This is considered to be an unreliable technique, but they also confirmed that the sand strata in which the skeleton was buried was of a similar age, using a more dependable technique called optically stimulated luminescence (OSL), which measures how long it has been since quartz crystals were exposed to sunlight.
Now, New Scientist reports that the same Australian team (and three others) have revised their date, claiming that the burial of Mungo Man took place 40,000 years ago. The new dates were also derived using the OSL technique. But the main difference this time around was that they sampled sand from the exact burial sites, rather than from 400 metres away, as they apparently did in the original study. They have also dated stone tools found at the site to 50,000 years ago. These revised dates are in line with archaeological evidence that humans lived in northern and western Australia 50,000 years ago.