COLUMN: Geologists looking at recent sediments: White Sands ancient human footprints 

Three localities in New Mexico have provided significant findings in the understanding of human occupation in North America.

After studying deposits containing extinct bison bones in Folsom and mammoths near Clovis in the early 1900’s, geologists recently investigated the White Sands. There, recent discoveries by quaternary geologists who specialize in examining geologic deposits that were formed in the past thousands of years rocked North American archaeology.

The White Sands area in southern New Mexico contained a large lake during periods of much wetter climate than present. Mammoth footprints were known at the site since the early 1900s, and human footprints were also later observed.

The park operators requested that U.S. Geological Survey (USGS) geologists date the footprints. Most scientists would have expected the resulting ages to be 13,000 years or younger. Detailed inspection by geologists from the USGS and park scientists showed the layers that contained the footprints were gypsum-rich alluvium layers interlayered with clay and silt.

These sediments were deposited during alternating wet and dry environments along the eastern margin of the former lake (Lake Otero) in the Tularosa Basin. The geologists noticed the presence of seeds from an aquatic plant within thin clay layers interbedded with the footprint horizons or embedded in the footprints themselves.

Eleven samples from those seeds were tested for radioactive carbon 14 age dating, and the results indicated a 21,000 to 23,000 age! This unexpectedly old age caused scientists to check their data multiple times, and the results were then published in 2021.

That publication created quite a controversy, with criticism that the seeds from the aquatic plants could have been in contact with “older” water. Many archaeologists remained skeptical.

As soon as the Covid crisis was over, the USGS scientists went back to the site and through very laborious processes collected two types of dating material: pollen grains for C-14 dating from terrestrial plants (which would not have been contaminated with older lake water) and quartz grains (which were rare in the mainly gypsum layers) for optically stimulated luminescence (OSL) dating.

The resulting ages from these two independent methods were surprisingly similar to the earlier findings, causing most scientists to now accept the age of the footprints at 21,000 to 23,000 years, although some scientists remain skeptical.

The age of the footprints indicate that humans were active in Southern New Mexico during a period of widespread ice cover in North America. At that time there was no path through the ice covering Canada and the northern U.S. for the migration of people from Asia to the Americas. Any path along the coast, with towering ice shelves along the coastlines and no food access, must also be eliminated as a possibility.

Therefore, humans must have migrated here much earlier. This finding at White Sands brought a very strong set of data against the “Clovis First” theory that called for the earliest arrival of humans crossing from Asia at the Bering Straight land bridge from Asia around 13,000 years ago.

Additionally, scientists studying the mile-long set of human footprints recognize the movements of teenage-age humans and their interaction with large animals such as mammoths and giant sloths. Thousands of individual footprints have been mapped, photographed and documented before the footprints are destroyed by the harsh weather and gypsum nature of the layers.

The footprints offer a unique opportunity to relate to our human ancestors. No artifacts (wooden tools, arrowheads, sandals remnants) have yet been found at the site.

(Paul Parmentier is a retired geologist from California now living in Los Lunas. He shares the rich geology and nature features in Valencia County in a monthly column.)