Yukta Kulkarni ’22
Humans have been populating Earth for hundreds of thousands of years, mainly inhabiting areas in East and South Africa. It was thought that humans had first arrived in the Americas around 15,000 years ago. However, new findings from excavations at Chiquihuite Cave in central-northern Mexico provide evidence that humans could have been present thousands of years earlier than originally predicted, an estimation of about 33,000 years ago.
Chiquihuite Cave is located in the Astillero Mountains approximately 1,000 meters above the floor of the valley and has multiple excavation sites. Two strata, or layers of rock, were identified to be used as chronostratigraphic markers (marking the age of the strata with respect to time). From these strata, bones, charcoal, and sediment were used for radiocarbon dating and optically stimulated luminescence dating. One younger stratum was estimated to be around 16,000 years old. The other stratum was gauged to have been formed before the Last Glacial Maximum (LGM), which is the last time that the glaciers were at their greatest size, around 33,000 years ago. The researchers deduced that the chronological sequence specified by the samples agreed with the composition and arrangement of the strata. Further evidence that demonstrates early human occupation are the stone tools discovered in the older stratum. Stone morphed into unnatural shapes indicates that something existed at this location to carve them. Additionally, extractions were executed on samples to test for environmental DNA. Researchers found that during the LGM era, a mix of forest species such as junipers, firs, pines, and grasses were present.
Strata chronostratigraphy, the presence of stone tools, and a lush environment all lead to the conjecture that humans were living in the Americas more than 30,000 years ago. It is also believed that humans were present here frequently, possibly as a result of migratory behaviors. Since the cave is located at a high elevation, any humans that may have passed through were acclimated to the environment. More excavating and DNA sampling must be done to confirm the presence of humans. For now, it is amazing to think that the first human in the Americas lived tens of thousands of years ago, a simple idea that could change the history of humans as we now know it.
 C. Ardelean, et al., Evidence of human occupation in Mexico around the Last Glacial Maximum. Nature 584, 87-92 (2020). Doi: https://doi.org/10.1038/s41586-020-2509-0
 Image retrieved from: https://commons.wikimedia.org/wiki/File:MANOT_CAVE_EXCAVATION.JPG
Byline: New evidence suggests that there was human presence in the Americas 15,000 years earlier than we had previous thought, for a total span of approximately 30,000 years.