HUMAN EVOLUTION

The Last Continent

~23,000 to 15,000 years ago (earliest dates disputed)

Phanerozoic · Cenozoic · Quaternary · Pleistocene · Late Pleistocene

The Americas were the last habitable continent people reached, by way of the land bridge at Beringia and the Pacific coast below it. Footprints at White Sands, in New Mexico, lie between layers of seeds dated to about twenty-three and twenty-one thousand years ago, which would put people there during the coldest part of the last ice age. That chronology was challenged in Science and defended in the same issue. Widespread occupation from about fourteen thousand seven hundred years ago, as the climate warmed abruptly, is not what is in dispute.

Why it matters

Two questions meet here and will not separate: when people arrived, and why eighteen genera of large mammals stop appearing shortly afterwards. The earlier the arrival is pushed, the longer humans and mammoths shared the land, and the harder it becomes to blame the extinctions on a sudden encounter.

Dating & uncertaintyDisputed

Footprints at White Sands are bracketed by seeds dated to 23,000 to 21,000 years ago, which would put people in North America during the glacial maximum. Those dates have been challenged, on the grounds that old carbon dissolved in the lake water could have made the radiocarbon ages thousands of years too old, and defended in the same issue. Widespread occupation from about 14,700 years ago is not contested.

Sources

1. Bennett et al. (2021), Science · Evidence of humans in North America during the Last Glacial Maximum
2. Madsen et al. (2022), Science · Comment on Evidence of humans in North America during the Last Glacial Maximum
3. Becerra-Valdivia & Higham (2020), Nature · The timing and effect of the earliest human arrivals in North America

Earth history as one day

23:59:59.56438 ms before midnight

if Earth’s 4.54 billion years were compressed into a single day