This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Some 23,000 years ago, during the coldest part of the last ice age, people walked across the muddy margins of an ancient lake in what is now White Sands National Park, New Mexico. The footprints they left behind have transformed our understanding of when people first reached the Americas.
When we reported dates for the White Sands footprints in 2021, our findings were met with controversy. They placed people in North America thousands of years earlier than other widely accepted sites. Subsequent work using several independent dating techniques strengthened that chronology.
Our latest research takes the story a step further. Rather than simply asking when people were at White Sands, we can begin to ask: What sort of world did they experience? Our work is published in Science Advances and Fossil Studies.
The answer is a surprisingly dynamic one that was marked by periods of rapid climate change. Our expanded excavations at White Sands have identified 20 different horizons or packages of sediment containing human footprints. Together they span almost two millennia, from about 23,500 to 21,700 years ago, firmly within the last glacial maximum (the height of the last ice age).
Alongside the footprints, the sediments contain a remarkable archive of environmental change. Pollen records the vegetation growing around the basin, while organic molecules preserved in the sediment—including waxes originally produced by plant leaves—provide information about temperature and rainfall. Together, these allowed us to reconstruct the landscape through which people were walking.
At the beginning of the record, White Sands looked very different from today. A large body of water, Lake Otero, occupied much of the basin. The surrounding mountains supported conifer forests and average annual temperatures were around 4°C colder than today.
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