A period of extreme cooling in western Europe may have driven away the continent’s earliest human species, leaving the region devoid of hominins for about 200,000 years, a new study suggests.
Previously, scientists assumed humans had continuously occupied Europe since they first arrived more than a million years ago. But the new analysis, published last week in Science, points to an era devoid of historical evidence of humans.
This period, researchers say, coincided with a freeze. Tzedakis and his colleagues reconstructed the past climate by analyzing a deep-sea sediment core taken off the coast of Portugal. In the layers of prehistoric sediment, organic molecules produced by marine plankton provided a window into sea conditions, and buried pollen grains preserved a record of land vegetation. By putting this data into computer simulations, the researchers found a previously unknown period of cooling about 1.15 million years ago.
During this cooling, average winter temperatures plummeted by 9 to 13 degrees Fahrenheit in the eastern Atlantic, per a statement from London’s Natural History Museum. Air temperatures in the usually mild Mediterranean dropped well below freezing, writes BBC News’ Pallab Ghosh.
“Such a large change in temperature would have hit these humans hard, and they didn’t quickly recover,” Chris Stringer, a Natural History Museum scientist and co-author of the paper, says in the statement. “It would have led to changes in the flora and fauna as well, which could have left these humans with limited food options. Smaller cold stages later on would have delayed any recovery further, meaning that western Europe was probably depopulated for a long period of time.”
The first hominids to arrive in Europe from Africa were likely Homo erectus, a species of early humans with modern human-like body proportions. Fossils and stone tools from H. erectus that date to around 1.8 million years ago have been unearthed in Georgia. Evidence of the species dates to about 1.4 million to 1.5 million years ago in Italy and southern Europe and to about 1.2 million years ago in Spain.
Then, according to the new findings, the cold snap hit around 1.15 million years ago, causing early humans to either leave the area or die off. The frigid conditions likely extended along the Mediterranean coast, perhaps as far as southwestern Asia, per the museum statement. It wasn’t until between 850,000 and 950,000 years ago that humans returned to Europe, the researchers say. These humans, possibly the more advanced species Homo antecessor, were likely much more resilient to the cold, with “evolutionary or behavioral changes that allowed survival in the increasing intensity of glacial conditions,” Tzedakis tells Will Dunham of Reuters.
The cooling period was likely caused by the melting of an ice sheet that covered the Arctic and parts of North America and Europe, creating an influx of freshwater that would have weakened a vital ocean current called the Atlantic Meridional Overturning Circulation by up to 95 percent. Researchers recently predicted a weakening of this current again, which they say could occur within this century because of human-caused climate change.
Michael Petraglia, a paleoanthropologist and director of the Australian Center for Human Evolution at Griffith University who was not involved in the study, tells Live Science the paper “made good sense” and could be relevant for current climate change research.
“The environmental, fossil and archaeological evidence are in good agreement for regional abandonment and perhaps even the extinction of early [human] populations,” he tells the publication. “This is a story of how climatic variability had profound effects on hominin populations in the past, with implications for all of humanity today who face extreme weather events and changes in ecosystems.”