11 October 2023
New research confirms that a fossil of human footprints found in the U.S. state of New Mexico likely represents the oldest direct evidence of humans living in the Americas.
The footprints were discovered at the edge of the remains of an ancient lake in White Sands National Park in southern New Mexico. The research, published recently in Science, suggests the fossil dates back to between 21,000 and 23,000 years ago.
The estimated age of the footprints was first reported in Science in 2021. But some researchers questioned the dates. Researchers wondered whether seeds from lake plants used in the early dating may have taken in ancient carbon from the lake. If so, this could have changed the radiocarbon test result by thousands of years.
The new study presents two additional lines of evidence for the older date range. It uses two different materials found at the site, ancient tree pollen and quartz grains.
The reported age of the footprints questions the belief that humans did not reach the Americas until about 15,000 years ago. That was a few thousand years before rising sea levels covered the Bering land bridge between Asia and North America.
Thomas Urban is a scientist who studies ancient humans at Cornell University in New York. He was involved in the 2021 study but not the new one. He said it is an area "... that's always been controversial..." Urban said such studies are important because they deal with the last part "of the peopling of the world."
Thomas Stafford is an independent scientist who studies ancient humans and the Earth in Albuquerque, New Mexico. He was not involved in the study. He said that while he "was a bit skeptical before," he now believes it.
Stafford said it is an important finding if three completely different methods show findings from a similar time period.
The new study separated about 75,000 individual pieces of pollen from the same area in rocks where the footprints where found.
Kathleen Springer is an Earth scientist researcher at the United States Geological Survey and helped write the new paper. She said the process of dating pollen is very difficult. She added that scientists believe radiocarbon dating land plants gives more correct results than dating plants living in water. But she added there needs to be a large enough number of plants to study.
The researchers also studied damage to the structure in ancient small pieces of quartz to produce an age estimate.
Ancient footprints of any kind – left by humans or large animals – can give scientists some idea when they are from. They may record how and where people or animals walked and if their paths crossed. Animal footprints have also been found at White Sands.
Other ancient sites in the Americas point to a similar time period. These include ancient art made from animal remains in Brazil. But scientists still question whether such materials really suggest that humans were living in the Americas then.
Jennifer Raff is a scientist who studies ancient human genes at the University of Kansas. She was not involved in the study. Raff said, "White Sands is unique because there's no question these footprints were left by people, it's not ambiguous."
I'm Andrew Smith.
Christina Larson reported this story for The Associated Press. Gregory Stachel adapted the story for VOA Learning English.
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Words in This Story
fossil – n. something (such as a leaf, skeleton, or footprint) that is from a plant or animal which lived in ancient times and that you can see in some rocks
controversial – adj. relating to or causing much discussion, disagreement, or argument
skeptical – adj. having or expressing doubt about something (such as a claim or statement)
unique – adj. used to say that something or someone is unlike anything or anyone else
ambiguous – adj. able to be understood in more than one way