When Did Humans Cross Land Bridge? Perhaps Immediately

It emerged later than previously believed, just under 36K years ago: study
By Arden Dier,  Newser Staff
Posted Jan 4, 2023 1:23 PM CST
When Did Humans Cross Land Bridge? Perhaps Immediately
The landscape of Bering Land Bridge National Preserve is shown on Aug. 14, 2013.   (Wikimedia Commons)

New research indicates the ice sheets that covered North America during the last ice age developed "surprisingly quickly and much later in the glacial cycle than previous studies had suggested"—and the implications could be big. There's been much debate about when the Bering Land Bridge that once connected Asia to North America was able to have been traversed. We know that sea levels fell as water became locked in ice sheets during the peak of the last ice age, known as the Last Glacial Maximum (LGM), which lasted from 26,500 to 19,000 years ago. But according to study author Tamara Pico of UC Santa Cruz, "more than 50% of the global ice volume at the [LGM] grew after 46,000 years ago," which "implies that there was a substantial delay in the development of ice sheets after global temperatures dropped."

Researchers reconstructed the sea level history by analyzing nitrogen isotopes in the remains of marine plankton taken from seafloor sediments in the western Arctic Ocean and identified a signature indicating when the waters of the Pacific Ocean flowed into the Arctic Ocean, and when they did not. "Some of the ice sheet histories that have been proposed differ by quite a lot, and we were able to look at what the predicted sea level would be at the Bering Strait and see which ones are consistent with the nitrogen data," Pico says in a release. According to researchers, the Bering Land Bridge emerged around 35,700 years ago and remained traversable during the LGM when "ice volume increased rapidly."

The study findings "shorten the time between the opening of the land bridge and the arrival of humans in the Americas," according to a release. "People may have started going across as soon as the land bridge formed," says Pico. Previous genetic findings suggest humans lived along the Beringia gateway as early as 30,000 years ago and reached the Americas by 16,500 years ago. However, new discoveries—including stone tools in Mexico dated to as early as 32,000 years ago—have led to theories suggesting the first humans in the Americas crossed not the land bridge, but either the Atlantic Ocean or Pacific Ocean by boat. The land bridge would've remained passable until 11,000 to 13,000 years ago, when it was flooded again, according to the study, published last week in PNAS. (More Bering Land Bridge stories.)

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