May 21, 2012
Greece should be filled with hominid bones and stone tools. Its location makes it the perfect gateway to Europe for the earliest hominids leaving Africa, and even during dry and cold spells that made many other parts of the world uninhabitable, Greece remained pleasant. Yet the country’s archaeological record is bare from 1.8 million to 125,000 years ago, a period known as the Early to Middle Pleistocene.
And here’s why: Only 2 to 5 percent of Greece’s paleoanthropological record from this period has survived. That’s the conclusion of the authors of a new study in Quaternary Science Reviews that looks at the geological processes that preserve or destroy bones and artifacts.
To be fair, Greece’s record isn’t completely empty. Anthropologists have found some handaxes and a few skulls, a Homo heidelbergensis in the cave of Petralona and two Neanderthals in Apidima. The problem is that these finds are poorly dated. Many of the discoveries have been made on the surface, meaning there’s no geological context or stratigraphy—the depositional layers that build up in a sequence over time—to help researchers figure out when the fossils and tools were left behind. And without dates, these pieces of evidence are hard to interpret.
One explanation for the lack of discoveries is that hominids never really set down roots in the area. If they didn’t live there, there was nothing to leave behind. Vangelis Tourloukis of the University of Tübingen in Germany and Panagiotis Karkanas of Ephoreia of Palaeoanthropology–Speleology of Southern Greece don’t buy this explanation. So they looked to the region’s geology to solve the puzzle of the missing hominids, reviewing a range of previous studies.
One thing they considered was the changing sea level over time. During cold periods, more of the world’s water is locked in polar ice sheets and glaciers, and sea level recedes, exposing parts of the seafloor. When it gets warm again, the ice melts and the ocean rises. Tourloukis and Karkanas found that during parts of the Early and Middle Pleistocene, much of the Aegean Sea, east of Greece, was dry land. In fact, the total area that was exposed then equals the area of the Greek Peninsula today (more than 50,000 square miles). If you assume all dry land was a possible living site of hominids, that means half of the potential archaeological record is now gone, submerged beneath the Aegean, the researchers say.
Back on dry land, a range of climatic and geologic factors influenced the likelihood that bones and artifacts were preserved. One of the biggest contributors was water: Rivers and streams eroded the landscape, washing sediments (and artifacts) away and piling them up somewhere else. In the Early and Middle Pleistocene, climatic conditions led to periodic catastrophic flooding, the researchers noted, and “archaeological assemblages [were] subjected to disturbance, reworking or total destruction every few thousands, hundreds or even tens of years.”
Tectonic activity, the movement within Earth’s crust and mantle that shapes topography, caused further problems. Greece is a very tectonically active region, and in the Early and Middle Pleistocene, the crust was being stretched. At one point, the stretching changed directions, raising blocks of earth and exposing bones and artifacts to destructive erosion for thousands of years. (Meanwhile, some blocks were buried, which helped protect artifacts. Such basins are probably where most potential archaeological sites are today.)
Another issue is Greece’s rugged, steep terrain. More than half of the country is mountainous or hilly, where landslides can easily bury or destroy archaeological sites.
After reviewing this geological evidence, the pair’s final step was to estimate how much of Greece’s archaeological record from this period may still exist. This takes a little bit of math. Here are the important numbers:
10 percent: Not all of Greece’s land is composed of Early to Middle Pleistocene-aged deposits. Sediments from other time periods also make up the landscape. The researchers estimated about 10 percent of the Greek Peninsula is dated to this period.
40 percent: This is the area of Greece that isn’t too steep and mountainous for fossils and tools to be preserved over time.
50 percent: Right off the bat, the researchers eliminated half of the potential archaeological record because it’s now at the bottom of the Aegean Sea.
So, the amount of the potential archaeological record that may still be out there is 10 percent of the 40 percent of the 50 percent—or just 2 percent. With some tweaks in their expectations and assumptions, the researchers say it could be as high as 5 percent.
These odds don’t seem great, but Tourloukis and Karkanas have an optimistic outlook. Because so much more land was exposed in the past, forming a natural land bridge with Turkey, hominids dispersing from North Africa through the Sinai Peninsula and the Middle East could have easily followed the southern coast of Turkey into coastal Greece and then on to Italy and the rest of Europe. And the geological evidence suggests the landscape would have been home to numerous lakes, lagoons, marshes and streams rich in valuable plant and animal resources. Why wouldn’t hominids have wanted to live there?
With this new assessment, archaeologists now have a better chance of finding traces of these hominid Shangri-Las.
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