The revised dating and uncovering of new artifacts from an archaeological site in Australia’s Arnhem Land has prompted archaeologists to revise theories as to when the ancestors of present-day Aboriginies first settled in what we now call Australia, pushing that date back by 20,000 years to a point in time 65,000 years ago. This revised timeline also implies that modern humans may have begun the colonization of Asia much earlier than previously assumed.

As an archeological site, the Madjedbebe rock shelter has been a major point of contention for archaeologists debating as to when Australia was first colonized, with the two main camps arguing a date for either roughly 60,000 years ago, or sometime after 50,000 years ago. Genetic studies failed to settle the debate, showing a wide range of dates that encompassed both theories. Madjedbebe (also known as Malakunanja II) was first excavated in the late 1980s, when the dating of the artifacts found there produced the then-controversial age of 60,000 years.

Armed with more modern dating techniques, researchers re-excavated the site in 2012 and 2015, uncovering hundreds of thousands of previously-undiscovered artifacts, including the world’s oldest known ground-stone axes, grindstones used for processing seeds, "huge quantities of ochre", and the world’s oldest examples of the use of mica for artistic purposes.

Employing an advanced form of thermoluminescence dating called optically stimulated luminescence (OSL), soil samples that surrounded the artifacts were found to be between 60,000 and 70,000 years old, making for an average age of 65,000 years.

However, the results of earlier genetic studies imply that these early inhabitants might have been from a different population: while settlement in Arnhem Land may have occurred 65,000 years ago, genetic evidence gathered from modern Aboriginies imply that their ancestors didn’t interbreed with Neandertals and Denisovans until between 45,000 and 53,000 years ago, meaning they didn’t enter the area until sometime later.

"If these [new] dates are correct, they must be from a human population that was largely replaced by the people who are the primary ancestors of today’s Australians and New Guineans," explains Harvard University geneticist David Reich. 

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