First humans in America experienced dramatic climate change

A new study has revealed that the first people to arrive in the Americas had to adapt to several extreme changes to the environment during the last ice age, over 20,000 years ago.

The study builds on previous research led by Bournemouth University and the US Geological Survey (USGS), which found footprints in New Mexico dating back 23 thousand years. These findings rewrote history by pushing back the date of earliest known human activity in the Americas by several thousand years.

“Our latest research now takes the story a step further. Rather than simply asking when people were living there, we can begin to ask: what sort of world did they live in?” said Dr Sally Reynolds, Associate Professor in Hominin Paleoecology at Bournemouth University and co-author of the study.  

During the earliest period they studied, 24,200 years ago, White Sands National park featured a large body of water, Lake Otero, which was surrounded by mountains covered in conifer trees. This was during the last ice age and temperatures were around 4°C colder than today.

The climate began to change over the next 2000 years as temperatures rose. The conifer forests were replaced by oak trees and sagebrush and the lake started to shrink. Also during this time, the lake became more saline and plants that were better suited to drier conditions grew more abundant. 

“Throughout these periods of change the people continued to visit and live in this area,” said Dr Reynolds. “The sediments containing their footprints show us their environment changed significantly within individual human lifetimes,” she added.

To understand the changes to the environment during this period, the researchers took sediment samples containing ancient pollen which revealed the types of plants growing in the region. The samples also contained organic molecules, such as waxes from plant leaves and membrane lipids produced by archaea and bacteria that gave information about rainfall, temperatures and aridity. 

The research team say it is possible that the different climates attracted people to the area because of the availability of food. For example, a shrinking lake might have led to a higher concentration of animals and plant life.

“This study fulfilled a long-term research goal at White Sands – to expand the originally published footprint site and sample for environmental indicators to help further our understanding of the complete context of conditions at the height of the Last Glacial Maximum. It’s remarkable that early humans in the region were real-time witnesses to a rapidly changing environment discernible within a human lifetime – that is really food for thought,” said Kathleen Springer, US Geological Survey research geologist and co-lead author on the current Science Advances paper. 

A previous study led by Dr Reynolds and Professor Matthew Bennett, University of Reading, with the USGS also revealed that the people there developed the earliest known form of human transport. 

However, they also caution that whilst the footprints show that people were in the area throughout this period, they cannot determine precise human movements and behaviours.

Dr Reynolds added, “The footprints give us a snapshot of the people who lived there over 20,000 years ago. But they are not a continuous movie of their lives. They are individual frames – showing moments when humans, mud, water and chance came together.”

This latest study has been published in Science Advances.