A year ago, when Josep Par´es first told Eudald Carbonell how old he thought a certain layer of rock in north central Spain was, Carbonell’s response was simple but dramatic. If you are wrong,’’ he told his colleague, a geologist, this will be the end of your career. The rock, from a site called Atapuerca, contained remains of human ancestors, and Par´es’s date indicated the bones were far older--and more important--than anyone had previously believed.
Par´es’s career is safe. His dates, checked and rechecked and announced last August, show that those bones and the stone tools found with them are at least 780,000 and probably close to a million years old, making them twice as old as any other European ever found. And so Carbonell, who works at Rovira i Virgili University in Tarragona, Spain, and is the leader of the archeological team at Atapuerca, can now say with some confidence, Between 800,000 and one million years ago there was an important hominid presence in Europe, without fear of contradiction.
Together with some million-year-old stone tools uncovered this year at another Spanish site known as Orce, the finds are giving researchers their first sense of who colonized Europe. The hominids represented by the bits and pieces of bone--four individuals, including one child--look quite primitive and could be a new species, possibly distant ancestors of the Neanderthals, who didn’t appear until about 200,000 years ago.
Precisely what happened in Europe before the Neanderthal presence has troubled anthropologists for some time. They generally believe that our ancestor Homo erectus hotfooted it out of Africa at least a million years ago, reached the Middle East, and then--according to all the available evidence--stubbornly, repeatedly, turned right. Erectus sites have shown up in India, in China, in Indonesia. But Europe was a complete blank.
The fossils now filling in that blank come from a limestone cavern at Atapuerca called Gran Dolina. And the dates for the fossils have been etched in the stacked layers of Gran Dolina rock by Earth’s magnetic field. When that rock was forming, magnetic grains in the sediment took on the orientation of Earth’s field, like tiny compass needles. But Earth’s magnetic field flips every so often, sometimes pointing toward the North Pole and sometimes toward the South Pole, and the compass needles in the different rock layers record those flips. Since the flip chronology has been well established, the direction of the needles in any given layer can give an approximate age to the rock.
The last major flip, marked by what is known as the Matuyama- Brunhes boundary, happened about 780,000 years ago, when the field swung from south to north. There are 11 stratigraphic layers of rock at Gran Dolina, and the Matuyama-Brunhes signature was originally thought to be near the bottom of the stack. That meant the higher layers--including the one bearing the fossils, TD 6, which is in the middle of the stack--had to be quite a bit younger. So when Carbonell and his colleagues first found bones in TD 6, in 1994, they were pleased, but they didn’t think they had anything remarkable.
Then Par´es, who works at the CSIC Institute of Earth Sciences in Barcelona, became suspicious of the magnetic chronology. Chemical weathering in rocks can cause false signals--near the surface of the rock it creates a new mineral whose grains can take on the orientation of the current normal’’ magnetic field. In the Gran Dolina stack, that weathering would make the layers on top seem younger than they really were and would move the Matuyama-Brunhes boundary lower down. Par´es, seeing signs of such weathering, heated samples from each layer to remove such misleading overprints’’ and measured the underlying magnetic imprint. The result: The true flip boundary lay not below TD 6 but some distance above it. That meant the fossils suddenly aged by several hundred thousand years, and the hominids could have arrived in Europe not long after Homo erectus emigrated from Africa.
Although the European fossils are now the same age as some erectus specimens from Southeast Asia, they look decidedly different. Details of the face make it look like a northern African hominid, Homo ergaster, while aspects of the jaw resemble those of a species called Homo heidelbergensis, which appeared in Europe about 400,000 years ago and may have given rise to the Neanderthals. Tracing the connections promises to be quite interesting, but it’s going to take more bones.
We’re beginning to get a database from Spain, of all places, where we had absolutely zero, says F. Clark Howell, an anthropologist at the University of California at Berkeley who has worked closely with the Spanish team. The question, he says, is, Was this a fluky thing that sputtered out like a firecracker that didn’t quite light?’’ Or was it a successful colonization that lasted for millennia? And if erectus did turn left and cross into Europe, where are all the other fossil sites along the way to Spain?
I think there are more, says Howell, and sooner or later we’ll find them--hopefully in my lifetime. There should be bones in Italy and in France. But finding them is going to take a bit of luck. Looking for hominid remains is like apartment hunting in New York, says Howell. You have to know your geography, you have to find the right neighborhood. Then you look into a place and the kitchen just isn’t big enough. It takes a while.