1/7/2024 0 Comments Gorilla monsoonUsing a sensitive instrument in the UW–Madison Department of Geoscience called an ion microprobe, the team measured the relative amounts of light and heavy oxygen at seasonal increments across the growth bands of two 125,000-year-old speleothems from Soreq Cave. Orland and his colleagues hypothesized they might be able to discern from speleothems whether two rainy seasons had contributed to their growth at times in the past because they might show a similar signature of light oxygen in both winter and summer growth.īut to make this comparison, the scientists had to make isotope measurements across single growth bands, which are narrower than a human hair. Today, the water contributing to speleothem growth throughout much of the year has both heavy and light oxygen, with the light oxygen predominantly delivered by rainstorms during the winter wet season. “It could be important context for experts studying how, why, and when early modern humans were migrating out of Africa.”Īmong these isotopes are different forms of oxygen molecules - a light form called O 16 and a heavy form called O 18. The water contains chemical fingerprints called isotopes that keep a record, like an archive, of the timing and environmental conditions under which speleothems have grown. Speleothems, such as stalactites and stalagmites, form when water drips into a cave and deposits a hard mineral called calcite. To try to better understand this seasonality, Orland and colleagues looked at cave formations called speleothems in Israel’s Soreq Cave. Some studies examining a variety of evidence, including pollen records, ancient lake beds, and Dead Sea sediments, along with some climate modeling studies, indicate summers in the region may have, on occasion, been wet. Scientists, though, have found it difficult to determine what kinds of precipitation patterns might have existed in the prehistoric Levant. Before modern times, those hot, dry summers would have presented a significant barrier to people trying to move across the landscape. Courtesy of Ian Orlandįor as long as humans have kept records, winters have been wet and summers have been hot and dry in the Levant, a region that includes Israel, Syria, Lebanon, Jordan and Palestine. Ian Orland at Soreq Cave, Israel, where some calcite cave formations are 185,000 years old. “The Eastern Mediterranean was a critical bottleneck for that route out of Africa and if our suggestion is right, at 125,000 years ago and potentially at other periods, there may have been more consistent rainfall on a year-round basis that might enhance the ability of humans to migrate.” “It could be important context for experts studying how, why, and when early modern humans were migrating out of Africa,” says lead author Ian Orland, a University of Wisconsin–Madison geoscientist now at the Wisconsin Geological and Natural History Survey, in the Division of Extension. With increased summer precipitation there may have been increased vegetation, supporting animal and human migration into the region. The likely timing of these northward monsoon expansions corresponds with cyclical changes in Earth’s orbit that would have brought the Northern Hemisphere closer to the sun and led to increased summer precipitation. That’s because science hasn’t settled how many times modern humans left Africa, or just how many routes they may have taken.Ī new study published this week in the Proceedings of the National Academy of Sciences by American and Israeli geoscientists and climatologists provides evidence that summer monsoons from Asia and Africa may have reached into the Middle East for periods of time going back at least 125,000 years, providing suitable corridors for human migration. The finding suggested that modern humans, who originated in Africa, began migrating out of the continent at least 40,000 years earlier than scientists previously thought.īut the story of how and when modern humans originated and spread throughout the world is still in draft form. Last year, scientists announced that a human jawbone and prehistoric tools found in 2002 in Misliya Cave, on the western edge of Israel, were between 177,000 and 194,000 years old.
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