Science | The Atlantic
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A Dentist Found a Jawbone in a Floor Tile Recently, a man visiting his parents’ newly renovated home recognized an eerily familiar white curve in their tile floor. To the man, a dentist, it looked just like a jawbone. He could even count the teeth—one, two, three, four, five, at least. They seemed much like the ones he stares at all day at work.The jawbone appeared at once very humanlike and very old, and the dentist took his suspicions to Reddit. Could it be that his parents’ floor tile contains a rare human fossil? Quite possibly. It’s “clearly hominin,” John Hawks, a paleoanthropologist at the University of Wisconsin at Madison who also blogged about the discovery, told me in an email. (Hominin refers to a group including modern humans, archaic humans such as Neanderthals, and all of their ancestors.) It is too soon to say exactly how old the jawbone is or exactly which hominin it belonged to, but signs point to something—or someone—far older than modern humans. “We can see that it is thick and with large teeth,” Amélie Vialet, a paleoanthropologist at the Muséum National d'Histoire Naturelle in Paris, wrote in an excited email to me about the jawbone. “That’s archaic!”An international team of researchers, including Vialet, is now in contact with the dentist to study the floor tile. (I’m not naming him for privacy reasons.) This thin slice of jawbone has a story to tell—about a life lived long ago, in a world very different from ours. It is in fragments of hominin bone like this one that we begin to understand our past as humans.How could a hominin bone have ended up in someone’s tiled floor in the first place? Travertine, the type of rock from which this tile was cut, is a popular building material used perhaps most famously by ancient Romans to construct the Colosseum. Today, a good deal of the world’s travertine—including the floor tile with the jawbone, according to the dentist—is quarried in Turkey, from a region where the stone famously forms natural thermal pools that cascade like jewels down the hillside. Travertine tends to be found near hot springs; when mineral-rich water gurgles to the surface, it leaves a thin shell over everything that it touches. In time, the layers accrue into thick, opaque travertine rock. If in the middle of this process a leaf falls in or an animal dies nearby, it too will become entombed in the rock. “Fossils are relatively common in travertine,” says Andrew Leier, a geologist at the University of South Carolina.Hominin fossils, specifically, are rare, but at least one has been found in Turkish travertine before. In 2002, a Turkish geologist named M. Cihat Alçiçek discovered a slice of human-looking skull sitting on a shelf in a tile factory. He brought the 35-millimeter-thick fragment to John Kappelman, an anthropologist at the University of Texas at Austin, and later also to Vialet in Paris. The skull turned out to belong to Homo erectus, an archaic human species that walked the Earth more than 1 million years ago, long before modern humans. Vialet thinks the newly discovered jawbone could be just as old.Vialet and her collaborators are now hoping to extract the tile, ideally intact, from the hallway where it’s been cemented in place. (The dentist is soliciting suggestions on Reddit for how to do so without also destroying his parents’ floor.) Then, chemical signatures in the rock can be used to date the fossil. Vialet also hopes to generate a 3-D model of the jawbone with micro-CT scanning, tracing the curve of the mandible and the roots of the teeth to find anatomical clues about its origin.The teeth could prove to be the real gold mine. Their hard enamel likely contains carbon, oxygen, and nitrogen isotopes whose presence could hint at what the hominin once ate. Shooting high-energy X-rays at the teeth can also reveal how quickly they grew, which is useful because different hominins developed at different rates, Kappelman told me in an email. The spongy insides of teeth also tend to be good sources of ancient DNA. (Given the high temperature of the hot springs where travertine deposits form, Kappelman thinks DNA probably wasn’t well preserved, but extracting it is still worth a try.) Bit by bit, researchers will begin to piece together a portrait of the hominin, who died by a hot spring so many eons ago only to be unearthed and then cut into floor tile for someone’s home.Paleotonologists and quarries, as Hawks wrote in his blog post, exist in an “uneasy symbiosis.” The industrial extraction process unearths far more rock than scientists could ever hope to, but it leaves science at the whim of commercial practice. Alçiçek, the Turkish geologist who spotted the skull in the early 2000s, says far fewer fossils are being found in travertine quarries these days because the technology has changed. Twenty years ago, companies were able to extract only the “uppermost part of the travertine body, which is rich in fossils,” he wrote in an email, but now they can dig deeper, into layers devoid of fossils. Today, he says, discovering a fossil in the travertine quarries is rare.Industrial quarrying can also damage the fossils it does uncover. That Homo erectus skull, for example, was already chopped up by the time Alçiçek saw it, and the rest has never been found. In 2007, back when the skull discovery was first announced, his collaborator Kappelman mused in a draft of a press release about where other pieces might have ended up. “Turkish travertine is sold all around the world today,” Kappelman said back then. “Some lucky shopper at Home Depot might just be surprised to find a slice of Homo erectus entombed in her kitchen countertop.”To this day, Kappelman told me, he still goes straight to the travertine-tile section whenever he shops at Home Depot. The rest of this jawbone has to be somewhere.theatlantic.com