Humans Arrived in North America More Than 30,000 Years Ago, Study Suggests

Archaeologists have obtained radiocarbon dates for the faunal bones excavated from Coxcatlan Cave, a dry rock shelter located within the southern portion of the Tehuacan Valley, southern Puebla, Mexico. The dates for the bone samples from the early depositional levels of the cave ranged from 33,448 to 28,279 years old.

Coxcatlan Cave, a rock shelter located within the southern portion of the Tehuacan Valley in Mexico. Image credit: Andrew Somerville.

Coxcatlan Cave, a rock shelter located within the southern portion of the Tehuacan Valley in Mexico. Image credit: Andrew Somerville.

Coxcatlan Cave is a north-facing, dry rockshelter site in the southern portion of the Tehuacan Valley along the alluvial slopes of the Sierra Madre Oriental.

The cave is several meters above the valley floor on a low bluff. It extends approximately 30 m in length and 8 m in width.

Within the cave, archaeologists previously excavated to a maximum depth of 4 m, documenting 28 horizontal stratigraphic levels, or habitation zones, and 42 discrete occupational episodes.

The zones occupied by people who did not make or use pottery, referred to as the Preceramic zones, are the earliest levels of the rock shelter.

These zones have been divided into four cultural phases — the Ajuereado, El Riego, Coxcatlan, and Abejas phases — based on changes in the stone tool technology, basketry and woven matting, and settlement patterns.

The earliest evidence for human occupation in the Tehuacan Valley occurred during the Ajuereado phase.

“Even though previous studies had not dated items from the bottom of Coxcatlan Cave, we were not expecting such old ages,” said Dr. Andrew Somerville, a researcher in the Department of World Languages and Cultures at Iowa State University.

“The findings add to the debate over a long-standing theory that the first humans crossed the Bering Land Bridge into the Americas 13,000 years ago.”

“We weren’t trying to weigh in on this debate or even find really old samples. We were just trying to situate our agricultural study with a firmer timeline,” he added.

“We were surprised to find these really old dates at the bottom of the cave, and it means that we need to take a closer look at the artifacts recovered from those levels.”

Dr. Somerville and colleagues selected a sample of 17 bones — eight lagomorphs (hares and rabbits) and nine deer specimens — from the Ajuereado levels of Coxcatlan Cave for radiocarbon dating.

The findings provide the researchers with a better understanding of the chronology of the region.

However, questions still remain. Most importantly, is there a human link to the bottom layer of the cave where the bones were found?

“If closer examination of the bones provides evidence of a human link, it will change what we know about the timing and how the first people came to America,” Dr. Somerville said.

“Pushing the arrival of humans in North America back to over 30,000 years ago would mean that humans were already in North America prior to the period of the Last Glacial Maximum, when the Ice Age was at its absolute worst.”

“Large parts of North America would have been inhospitable to human populations. The glaciers would have completely blocked any passage over land coming from Alaska and Canada, which means people probably would have had to come to the Americas by boats down the Pacific coast.”

The results appear in the journal Latin American Antiquity.


Andrew D. Somerville et al. New AMS Radiocarbon Ages from the Preceramic Levels of Coxcatlan Cave, Puebla, Mexico: A Pleistocene Occupation of the Tehuacan Valley? Latin American Antiquity, published online May 19, 2021; doi: 10.1017/laq.2021.26


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