Age of the oldest human footprints in North America at White Sands park refined

White Sands National Park in New Mexico preserves human footprints that scientists regard as the oldest evidence of people in North America. A new study has refined their age: between 23,500 and 21,700 years. This was the time of the Last Glacial Maximum, that is, the period when the ice sheets reached their greatest extent.

The study was led by Jessica Tierney of the University of Arizona and Kathleen Springer of the US Geological Survey. The scientists examined fossil pollen, hydrogen isotopes in the waxes of plant leaves and the chemical composition of sediments. They dated the layers to an accuracy of roughly 50 years. The average temperature then was about 10 °C, whereas now it is close to 16 °C. The coniferous forest in the area gave way to sagebrush and oak steppe. During one abrupt warming, which is recorded in the Greenland ice cores as well, the pine forest yielded within 100 years to piñon and juniper, and the landscape grew very arid. Lake Otero, which occupied most of what is now the park, gradually shallowed and turned into a flat salt-encrusted basin.

Beside the human footprints, the tracks of mammoths, giant sloths and dire wolves have been preserved