“It’s a bit strange what you can see in these tracks,” said Kathleen Springer, study co-author and US Geological Survey researcher. “And there was a hint that (the tracks) might be old.”
To prove it, the researchers focused on a set of exposed footprints that disappeared into the side of a small climb.
They first used ground-penetrating radar to confirm that the fossilized tracks continued inside the slope. Then, in January 2020, they carefully dug trenches around the footprints to expose them and the surrounding rock layers.
Finally, Springer and his fellow USGS researcher Jeff Pigati collected encrusted ditch grass seeds above and below the tracks and used radiocarbon dating to determine their age.
What came back was remarkable. The footprints were laid around – and in one case below – seeds that were buried between 21,000 and 22,800 years ago, suggesting two millennia of human habitation along the glacial lake some 10,000 years ago. before the Clovis people.
These results are also not based on a few single seeds of ditch grass. Springer said they found “mats” of them, leaving little doubt that the seeds were dug up exactly where their host plants germinated, sprouted and died.
The research team has since linked what was found in the soil to a clear climate signal: a well-documented period of warming around 23,300 years ago that is said to have made the lake shrink, creating new places “for all of these. people (and animals) to dab in wet sand, ”Springer said.