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Prehistoric Climate Change May Have Encouraged Human Innovation

The development of complex tools and even art may have been spurred by shifts in weather
stone age ax



Flickr/Andrew Becraft

Today's scientists are scrambling to develop technology to cope with climate change; carbon capture technology, renewable energy and drought-resilient crops are just a few examples.

But researchers recently learned that ours isn't the first civilization to innovate as the Earth's climate shifts. A new study suggests "pulses" in technological innovation that took place between 280,000 and 30,000 years ago in present-day South Africa could have been driven by dramatic shifts in the region's weather conditions.

During this period, known as the Middle Stone Age, humans developed the first symbolic art, like engraved pieces of red ochre and ostrich eggshell containers. Artifacts such as pierced shells, likely used for necklaces, and relatively complex stone and bone tools have also been dated within this time frame.

"Looking at sources of stone used to make tools, it is clear that some have been transported for hundreds of kilometers, suggesting the existence of long-distance trading networks," Chris Stringer, merit researcher at the London Natural History Museum's Department of Earth Sciences and one of the paper's authors, said in an email.

However, these major technological and behavioral developments happened in irregular bursts, the reason for which has been a scientific enigma until now.

"Some of these cultural groupings developed very rapidly, but they also declined very rapidly," said Ian Hall of Cardiff University's School of Earth and Ocean Sciences in the United Kingdom, who also contributed to the report, published this month in the scientific journal Nature Communications.

"There had been a lot of debate about exactly what the mechanism may be for that, and climate was certainly discussed. But there was never any good evidence to suggest that there was a climate signature that matched the development," Hall said.

The researchers analyzed a marine sediment core collected off the coast of the Eastern Cape of South Africa, close to where the Great Kei River meets the ocean. About 100,000 years of river discharge is reflected in the sediments of this core, providing a detailed history of the region's hydrological conditions for the first time.

Tying warm, wet periods to richer archaeological finds
The Great Kei and other nearby rivers discharged sediment rich in iron oxides. By examining the ratio of iron to potassium in the core, the researchers learned that relatively abrupt changes in the precipitation levels took place during the Middle Stone Age.

These swift increases in precipitation and humidity, as reflected by higher levels of iron in the sediment core, were likely caused by global climate fluctuations.

During what are called Heinrich events -- natural but still largely unexplained fluctuations in the global climate -- the Atlantic Ocean's circulation slows substantially. This "bipolar seesaw behavior of the Atlantic Ocean," as the paper calls it, led to a southward shift in the Intertropical Convergence Zone, which carried the monsoon rains away from sub-Saharan Africa and into the South African region.

As a result, large swaths of sub-Saharan Africa would fall into drought, the study says, while southeast Africa became warmer, wetter and more humid, transforming into prime real estate for early human groups. These events took place within millennia -- fairly quickly, on a climatic time scale -- and resulted in changes of up to 10 degrees Celsius in mean annual temperatures.

When comparing the history of hydrological changes in the region with artifacts from the Middle Stone Age, the researchers discovered a "striking correspondence between the archaeological record of South Africa and the timing of the abrupt climate change" as seen in the marine core, the study states.

"What we found is the warmer, wet conditions in southeast Africa matched almost precisely the timing of these cooling events in the north," Hall said. "All of the archaeological evidence fell within these wet and warm periods."

Although the reason why these conditions would spur early technological developments will require further study, the researchers theorize that higher, more concentrated human populations are more likely to develop new ideas. Recent findings suggest that when human populations fall under a certain population density level, cultural knowledge disappears over time, Stringer said.

"The opposite will occur if populations are relatively dense and interacting, as ideas can be built on, with more chance of being conserved," he said.

"The link between climate, population growth and innovation is also important for us today as we have been fortunate to have had a recent and long (about 10,000 years) period of relative warmth and climatic stability," Stringer added. "As a species we have thrived in terms of numbers and in terms of innovations, but rapid and adverse climate change could certainly threaten our success."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

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