INSUBCONTINENT EXCLUSIVE:
Some of the sediment layers contained the remains of ancient grass seeds mixed with the sediment
Bennett and his colleagues radiocarbon-dated seeds from the layer just below the oldest footprints and the layer just above the most recent
According to those 2021 results, the oldest footprints were made sometime after 23,000 years ago; the most recent ones were made sometime
before 21,000 years ago.At that time, the northern half of the continent was several kilometers below massive sheets of ice
sealed off the southern half of the continent from the rest of the world for the next few thousand years.
Ancient human footprints
found in situ at White Sands National Park in New Mexico.
Credit:
Jeffrey S
Pigati et al., 2023
Other researchers were skeptical of those results, pointing out that the aquatic plants (Ruppia
cirrhosa) analyzed were prone to absorbing the ancient carbon in groundwater, which could have skewed the findings and made the footprints
seem older than they actually were
And the pollen samples weren't taken from the same sediment layers as the footprints.So the same team followed up by radiocarbon-dating
This pollen came from pine, spruce, and fir trees, i.e., terrestrial plants, thereby addressing the issue of groundwater carbon seeping into
They also analyzed quartz grains taken from clay just above the lowest layer of footprints using a different method, optically stimulated
They published those findings in 2023, which agreed with their earlier estimate.
