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Footprints in time show early date for arrival of first Americans

Ancient humans made their way into America before the route was shut off by the Ice Age, arriving at least 6000 years earlier than previously thought, scientists have said.

In findings that could ‘‘revolutionise’’ the story of when humans first started to occupy the Americas, fossilised footprints discovered in New Mexico in the southern United States show that humans were present between 21,000 and 23,000 years ago. This was during a period known as the ‘‘last glacial maximum’’ when ice sheets were at their greatest southerly extent. The American heartlands were thought to have been inaccessible to humans at this time.

The question of when humans started to occupy the Americas has been fiercely debated, with the consensus settling on between 13,000 and 16,500 years ago.

For thousands of years prior to this, sea levels in the Bering Strait were low enough to allow humans to walk from Asia to Alaska but a wall of ice would have prevented them from travelling south into continental America.

It was not until about 13,500 years ago, as the Ice Age drew to a close, that ‘‘ice-free corridors’’ started to open up.

Some evidence has suggested that humans were present in the Americas 16,000 years ago, leading to theories that they may have been able to skirt down the Pacific coast by boat to get around the ice. Any evidence of human presence before this has been controversial. Stone tools from 27,000 years ago found in Mexico have been dismissed by some experts as naturally fractured rock fragments.

The discovery of human footprints up to 23,000 years old in New Mexico has now prompted an international team led by Matthew Bennett, a professor from Bournemouth University, to conclude that humans must have made their way south from Alaska earlier than previously thought, before the routes were cut off by ice between 23,000 and 30,000 years ago.

The ice sheets would then have extended behind them, effectively ‘‘isolating’’ that population in North America.

It also raises the possibility that humans were partly responsible for the extinction of species of ‘‘megafauna’’ in the region, including mammoths and giant sloths, that were previously thought to predate humans’ arrival.

The study, published in the Science journal, concludes: ‘‘The evidence presented here confirms that humans were present in North America before the glacial advances of the last glacial maximum closed the ice-free corridor and the Pacific coastal route and prevented human migration from Asia.’’

Loren Davis, an archaeologist at Oregon State University who was not involved in the research, told Science magazine: ‘‘If that’s true . . . it’s going to be a revolution in the way that we think about archaeology in the Americas.’’

The 60 clearly defined footprints were made by humans squelching through mud along an ancient lakeshore over more than 1500 years. Scientists were able to date the sediments around the footprints by carbon dating seeds in the surrounding rock, dating putting them between 21,130 and 22,860 old.

Bennett said: ‘‘This is unequivocal evidence of human presence at the height of the last glacial maximum, so 23,000 years ago.’’

He said it challenged the story that humans were ‘‘queueing at the door’’ in Alaska, waiting for the ice to melt.

A carbon dating expert at the University of Oxford said the team had done a ‘‘very sound job’’.

World

en-nz

2021-09-25T07:00:00.0000000Z

2021-09-25T07:00:00.0000000Z

https://fairfaxmedia.pressreader.com/article/282437057269311

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