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In a number of cases, the genetic evidence was located at stratigraphic levels where no hominin remains have been found.
“It was really exciting,” says Slon, “to see that even without the bones, we can still find the DNA of these people.” The technique worked even with sediments that had been collected a number of years ago and stored in labs, Slon notes, “so we’re not only restricted to active excavations.” The researchers hypothesize that the DNA in the sediments comes from body fluids left behind by hominins as well as decomposition of their remains.
They discovered pieces of charcoal in sediments at similar depths, and considered those to be proxies for the ages of the fossils themselves.
The charcoal bits were dated to around 19,000 and 13,000 to 11,000 years before present.
From 2007 to 2014, the team dug into a number of new areas near the center of the cave, he says.
Then, they found a powerful key with which to fully reconstruct the cave’s history: a buried “hill” consisting of layer upon layer of sediment, unaffected by erosion.
is generally thought to have spread throughout Southeast Asia’s islands and into Australia by about 50,000 years ago.
Now, many of the same scientists who made the discovery have radically revised their estimate of the fossils' age, based on an exhaustive new analysis of the cave’s geology.
About a year after the discovery, paleoanthropologist Thomas Sutikna, the new study’s lead author and a Ph. candidate at the Centre for Archaeological Research in Jakarta, pushed the team to take a closer look at the series of sedimentary layers, or stratigraphy, along the eastern wall.