Forget what J.R.R. Tolkien taught you about hobbits for a moment. In real life, Homo floresiensis, affectionately dubbed “the hobbit,” is a diminutive hominin species defined by skeletons discovered on the Indonesian island of Flores in 2004. Since then, its status and identity have been the subject of much speculation, mystery, and controversy. That's partly because the hobbits were thought to have lived startlingly recently—just 12,000 years ago.

The idea of another hominin species living as recently as 12 kya (12 thousand years ago) had been both exciting and incredibly confusing. “We know that modern humans had got to Australia ... probably by 50 kya,” Richard Roberts, one of the researchers involved in the work, told Ars. Modern humans had passed through Southeast Asia on their way there, which means that they must have existed alongside any species living in their path at the time. Flores is not too far off that path.

In fact, many originally argued that the Flores skeletons were those of modern humans. Rather than a new species, some researchers suggested a variety of ailments that could create skeletons with a similar set of features to those of the hobbits. This would have cleared up another mystery—where modern humans go, related species go extinct. “We could never work out how you could have hobbits surviving so long after modern humans had [arrived],” says Roberts.

But over time, a strong consensus built that Homo floresiensis really was something new, that no disease could create the full set of distinct features found on these skeletons. And now the people who discovered the skeletons are saying that their initial date that placed the hobbits so close to the present was based on a mistake. Instead, those researchers say the skeletons may even predate the arrival of modern humans in the area.

With so many of the initial issues regarding the skeletons clearing up, most researchers are ready to move on to the big remaining mystery: how do we fit Homo floresiensis into our increasingly complicated family tree? And, did modern humans have anything to do with their demise?

Error, luck, and timing

The critical date suggesting the hobbits lived recently had come from a piece of charcoal just two meters away from the most important specimen, which was called LB1. What the researchers hadn’t realized at first, when they had just four holes in the cave, was that the buried rock layers in the cave were very complex.

These layers formed a very steep slope, but it was covered up on one end by newer sediment, making it appear level. On the high side of the slope, the older layers are close to the surface; but on the lower side of the slope, even the youngest layers are quite buried. This means that digging one meter down in one part of the cave could hit very old sediment layers, but digging one meter down just a short distance away would leave you in much younger sediments.

The bones themselves weren't analyzed to calculate a date, Roberts explains. “Fossil people are very reluctant to destroy a brand-new skeleton to get a date out of it when you think you’ve already got it pretty well nailed.” And they did think they had it pretty well nailed—they dated pieces of charcoal from below, alongside, and above LB1, getting dates ranging from roughly 13 to 19 kya.

That distance of two meters, though, was critical. “We thought we were deeper than the skeleton and therefore safe, but we weren’t,” says Roberts. It turned out that even though some of the charcoal was below LB1 in depth, it was buried in a layer of sediment that was far, far younger. The steep slope had left the layers that contained the hobbit remains much deeper at the spot.

Matt Tocheri is an anthropologist who was brought onto the team after the initial discovery, and his role was to work on the details of the wrist bones that could help to classify the remains. He's candid about the fact that the initial date was way off base. Even if everyone did their job as best as they could have, he says, "We're all going to make mistakes."

At the same time, he points out that there was a hefty dose of bad luck in the way the discoveries took place. If the team had started digging just slightly south, he says, they would have discovered the details of the layout before reaching the critical remains.

Different factors lined up to lead the team into their error, Roberts says. "We were right down the bottom of a hole, it was the end of the field season, things weren’t at their very best. We’ve given up beating ourselves up over it, and we've just said, 'Let's just think what it is we did, what we missed, and are we absolutely certain now of what we think is going on?'"

Although Tocheri wasn't involved during the initial excavations, he was present as the team widened their excavation sites throughout the cave and slowly started to realize that something was wrong with their assumptions about the cave's stratigraphy. "This was a pretty big deal among the team," he says. "It was a big struggle. It took about three years before even a majority of the team was beginning to be convinced of what was going on."

Chris Stringer, a human evolution researcher at London’s Natural History Museum, considers the change in evidence an example of the scientific method in action. "Like any good scientists [the original team has] been prepared to revise and even falsify their previous conclusions," he wrote to Ars.

Rethinking the timeline

Worried about making another mistake, the researchers attacked the problem of establishing a more accurate date from every angle they could think of. They tested multiple samples with multiple techniques for years on end. "It’s been a long process, re-checking again, digging a new square to test it again," says Tocheri.

This time around, they did date the actual bones through uranium-series dating—a method that hadn’t been available in its most recent, most accurate incarnation in 2004. Uranium usually only enters bones via groundwater once they’ve been buried, where it decays slowly into thorium. As a result, the ratio of uranium to thorium can be used to measure how long the bones have been in the ground. Just a tiny bit of bone vaporized by laser can be used for uranium-series dating, so it leaves the fossils intact. This method placed the hobbit remains between 100 kya and 60 kya.

Infrared stimulated luminescence dating, another method not available to the team back in 2004, was used to date the sediments and layers surrounding the hobbit fossils. After collecting samples in the dark, individual grains of the ubiquitous minerals quartz and feldspar were analyzed to see how many electrons had been caught in “electron traps” inside the mineral grains. Because these traps are “emptied” by light, grains that have been buried for a long time accumulate more electrons in the traps. When light or heat is applied in a controlled setting, the emissions can be measured to work out how long that individual grain was buried.

These methods were used alongside the older techniques of carbon-dating and argon-argon dating to get information on a wide range of samples. The variety of methods was used to try to nail down as comprehensive a picture as possible, because it’s a tricky period to cover: the most well-used methods don’t really cover the period between 50 kya and 500 kya, says Pieter Vermeesch, a researcher not involved in the hobbit excavations. Vermeesch, like Roberts, is a geochronologist, studying the dating of rocks, fossils and sediments.

The time period gap is frustrating because it’s a vital window when it comes to studying our own evolutionary history, Vermeesch explains, but luminescence and uranium-series methods can help to fill the void. However, Roberts points out both of these methods have their own shortcomings: luminescence dating may be useable to date individual grains of materials that are incredibly common, but it lacks the precision of other methods. And uranium-series dating can’t tell us how long bones might have been in the ground before starting to absorb uranium; it can tell us that bones have been buried for at least a certain number of years, but it can't tell us that the bones were buried before a certain date.

“No dating method is perfect,” Roberts explains. But if you used different methods that are based on very different principles and they start to paint a coherent picture, then that means you’re more likely to be getting it right.

Listing image by North Carolina School of Science and Mathematics