In 2003, scientists made a startling find in a remote cave on the Indonesian island of Flores: The skull and skeleton of an adult female hominin, a group consisting of modern humans and extinct human species, who stood only about a meter tall.
In many places, these layers have been scoured by erosion, altered by seeping water, and jumbled by tectonic activity.
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.
The team then used numerous techniques to date the various sediments.
Dating on the gravelly sediment layer containing the fossils suggested it was deposited between 100,000 and 60,000 years ago; just above it is a layer of volcanic ash that was dated to about 60,000 years ago.
The charcoal bits were dated to around 19,000 and 13,000 to 11,000 years before present.
But Liang Bau boasts a devilishly complicated geological history, as layers of silt and clay interleave with layers of weathered limestone, loose gravel, and volcanic ash.
The team’s report of the much older dates of the sediments, as well as of the fossils themselves, suggest that the fossils could not have belonged to survived long enough to interact with modern humans remains an open question.
Meanwhile, Tocheri says the work is far from over in Liang Bua.
Rather than damaging the fossils by dating them directly, the team looked to the sediments in which they were found.
They discovered pieces of charcoal in sediments at similar depths, and considered those to be proxies for the ages of the fossils themselves.
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.