![\"Human](\"https:\/\/www.ecoticias.com\/en\/wp-content\/uploads\/2026\/10\/white-sands-human-footprints-track-package-15.jpg\")
Animal tracks cross the same surfaces. They belong to mammoths and their relatives, ground sloths, canids, possibly bears and a few birds. In one spot a large canid track sits right on top of a human footprint.<\/p>\n\n\n\n
Some layers also carry long grooves. The authors link them to people “dragging sticks or travois consisting of a single pole or crossed poles, presumably during the transport of resources.”<\/p>\n\n\n\n
Children and adults on the move<\/h2>\n\n\n\n
Foot length splits the walkers into four groups. Eight prints came from children under 4, and 72 from children about 6 years old. Twelve came from children near 12, and 60 from teens or adults.<\/p>\n\n\n\n
The sieved dirt held no stone tools or other artifacts. The authors found “no evidence for congregation or habitation” at the site. They write that “the travois features support the hypothesis of a transit site,” a place people crossed on their way somewhere else.<\/p>\n\n\n\n
“Even though these footprints have been buried in the gypsum mud for more than 20,000 years, they look like someone walked out on the playa yesterday,” Tierney said. “This is an incredibly rare opportunity to be able to do paleoclimate reconstruction and combine it with archeology in the same exact place.”<\/p>\n\n\n\n
Tree pollen checked the seed dates<\/h2>\n\n\n\n
The first dates, published in 2021, came from radiocarbon in seeds of Ruppia, a water plant that grew in the lake. Critics argued that old carbon in the lake water, known as the hard-water effect, could make those seeds look too old.<\/p>\n\n\n\n
“Although the veracity of the age estimates has been challenged, the chronology and supporting evidence remain conclusive,” the authors write. A second round of tests with conifer pollen and luminescence<\/a> had already backed the seed ages. But those pollen dates carried error bars of more than two millennia.<\/p>\n\n\n\n The university credits “innovative extraction procedures used to isolate up to 75,000 individual pollen grains per sample and refined dating methods used at the USGS Radiocarbon Laboratory.” The lab checked its process on pollen more than 110,000 years old from Snowmass Village, Colorado.<\/p>\n\n\n\n Pollen ran up to about 1,330 radiocarbon years younger than seeds from the same levels. The best of four age models puts Dansgaard-Oeschger event 2, a warming spike in Greenland ice, at about 23,200 years ago, give or take 300 years.<\/p>\n\n\n\n The researchers then studied the climate “at a timescale equivalent to a human generation, or approximately 50 years,” the university said.<\/p>\n\n\n\n “The White Sands sediments are unique in that they allow us to reconstruct environmental conditions during the last ice age at a very high temporal resolution, so that we can see fluctuations that were relevant for the humans present at that time,” Tierney said.<\/p>\n\n\n\n Tierney’s group in Tucson measured hydrogen isotopes in the waxy coating of ancient leaves, which track rainfall. The team also used fats from microbe membranes, known as GDGTs, to gauge temperature and salt. At the Universidad de Granada, where co-author Gonzalo Jim\u00e9nez-Moreno works, researchers counted 200 to 525 pollen grains per sample under a microscope.<\/p>\n\n\n “This tells us that local changes in aridity at White Sands were quite large and followed global climate shifts,” Tierney said.<\/p>\n\n\n\n From about 24,200 to 23,600 years ago, Lake Otero covered the trench site. During the last ice age the lake spread over most of what is now White Sands National Park. Conifers on the mountain slopes made up as much as 40 percent of the pollen, mostly pine.<\/p>\n\n\n\n Tierney said temperatures in the Southwest were generally cooler then, around 50 degrees Fahrenheit (10 degrees Celsius). Today’s annual mean in that area sits around 60 degrees (16 degrees Celsius).<\/p>\n\n\n\n Around 23,600 years ago the region began to warm, and the lake pulled back to the west. Oak and sagebrush replaced the conifer forest on the slopes. The warming sped up about 22,400 years ago, and the basin started to dry out.<\/p>\n\n\n\n Then came Dansgaard-Oeschger event 2. White Sands got less winter rain, and its water turned saltier. According to the university, pollen in the layers shows pine forest changing to pinyon and juniper, “all within about 100 years.”<\/p>\n\n\n\n That dry spell ended the open lake for good. A wet playa took its place, and the authors write that “humans and megafauna in the Tularosa Basin were able to travel across a newly exposed mosaic of wet and dry ground.” The oldest footprint layer in the trench dates to that same event.<\/p>\n\n\n\n Tierney said changing amounts of pollen from Ruppia, an aquatic plant that likes desert streams and springs, show Lake Otero rose and fell over about 1,500 years. In wet spells Ruppia made up more than 20 percent of the pollen, and as much as 60 percent.<\/p>\n\n\n\n “Eventually the lake shrunk more and more until it gave way to a flat playa,” Tierney said. “And throughout that whole sequence, people were walking there, leaving their tracks alongside those of mammoths, giant sloths and dire wolves.”<\/p>\n\n\n\n “Humans witnessed a complete floral turnover from conifer forest to sagebrush and oak steppe, the recession of pluvial Lake Otero, and centennial-scale swings in hydroclimate, including severe aridity during D-O 2,” the authors write.<\/p>\n\n\n\n People returned through all of it. The authors call the shrinking lake “a destination that was visited repeatedly for nearly two millennia by local residents and\/or people migrating through the basin.” That pattern, they add, “is a testament to the importance of the vital resources that were available there.”<\/p>\n\n\n\n “It’s remarkable that early humans in the region were real-time witnesses to a rapidly changing environment discernible within a human lifetime,” Springer said. She called it “really food for thought.”<\/p>\n\n\n\n Ed Jolie, the Clara Lee Tanner Associate Professor of Anthropology at the U of A, worked in the field on the dig. Jolie, who is Oglala Lakota and Hodulgee Muscogee, is also associate curator of ethnology at Arizona State Museum. He said the findings “humanize the deep Indigenous past of the Americas.”<\/p>\n\n\n\n “This research continues to remind scientists and the wider public that these resilient ancient human populations are the ancestors of contemporary Indigenous peoples, providing important scientific evidence in support of sovereign Native nations’ oral traditions and reinforcing the fact that we have been here since time immemorial,” Jolie said.<\/p>\n\n\n\n White Sands warmed while the Northern Hemisphere as a whole kept getting colder, from about 23,000 to 18,000 years ago. Its record looks more like sea surface data off California, where warming began as early as 26,000 years ago.<\/p>\n\n\n\n The authors write that the trench holds “the only quantitative temperature estimates for this region of the American Southwest.”<\/p>\n\n\n\n Fossils from Canada’s Yukon show that the ice age American cheetah, a close cousin of the puma<\/a>, roamed the same continent. Much later, people in Alaska left more than 80,000 objects at a 13,800-year-old base camp<\/a>.<\/p>\n\n\n\n “Biometric estimates were hampered by the small number of tracks on individual horizons,” the authors write. The team pooled all 152 prints to estimate ages and heights.<\/p>\n\n\n\n About 90 percent of the model runs gave a positive link between the two records. The closest fits needed the ice core clock shifted by about 100 years.<\/p>\n\n\n\n Next, the researchers want to learn what mechanisms could let a warming event in Greenland cause drying in the American Southwest.<\/p>\n\n\n\n The full study was published in Science Advances<\/a>.<\/p>\n\n\n\n The USGS, the National Science Foundation, Britain’s Arts and Humanities Research Council and the Western National Parks Association funded the work. The park service issued the dig permits at White Sands National Park<\/a>, and the University of Arizona<\/a> released the results.<\/p>\n\n\n\n Illustration: Karen Carr \/ University of Arizona<\/p>\n","protected":false},"excerpt":{"rendered":" In January 2022, a crew that included USGS research geologist Kathleen Springer and her colleague Jeffrey Pigati went back to … <\/p>\nClimate snapshots about 50 years apart<\/h2>\n\n\n\n
![\"USGS](\"https:\/\/www.ecoticias.com\/en\/wp-content\/uploads\/2026\/10\/white-sands-trench-springer-pigati-sampling.jpg\")
A lake that shrank to a playa<\/h2>\n\n\n\n
People kept coming back for nearly 2,000 years<\/h2>\n\n\n\n
A record unlike others in the Southwest<\/h2>\n\n\n\n
Open questions about the drought link<\/h2>\n\n\n\n