VOA慢速英语--在墨西哥发现的工具表明人类更早到达北美（在线收听）

Stone tools found in a Mexican cave suggest people were living in North America as early as 26,500 years ago, much earlier than past research has shown.

Scientists recently reported they had found 1,930 limestone tools in a mountain cave in Mexico's north-central Zacatecas state. The discovery included small flakes and fine blades that may have been used for cutting meat. Small points were also found that could have been used as spear tips for hunting.

Ciprian Ardelean is an archeologist at the Autonomous University of Zacatecas. He is the lead writer of a study on the findings that appeared in the publication Nature. Ardelean told the Reuters news agency the tools were between 31,000 and 12,500 years old. Traveling groups of hunter-gatherers lived in the area off and on for thousands of years.

Ardelean said it is possible some of the objects were even older than 30,000 years. But so far, the evidence is not strong enough to support that claim. Also, his team was unable to recover any human genetic material from the cave. "The peopling of America was a ... complex and diverse process," he told Reuters about the findings.

Tom Dillehay is a professor of anthropology at Vanderbilt University in Nashville, Tennessee. He was not involved in the study. He told The Associated Press that currently, the most widely accepted dates for the earliest known humans in North American are between 15,000 and 17,000 years ago.

A prehistoric stone tool found at a cave in Zacatecas in central Mexico is seen in this image released on July 22, 2020.

A prehistoric stone tool found at a cave in Zacatecas in central Mexico is seen in this image released on July 22, 2020.

Dillehay said the proposed date for the objects may be correct if further studies can confirm the results. However, he said he thinks they are probably not more than 20,000 years old, and most likely are between 15,000 and 18,000 years old. Dillehay does not question that some of the objects are probably man-made. But he said he would like to see further evidence of human use of the cave, such as cut bones and burned, plant-based food remains.

Ruth Gruhn is a professor of anthropology at the University of Alberta in Edmonton, Canada. In a Nature commentary, she said the results should bring new consideration to six Brazilian sites proposed to be older than 20,000 years. Those age estimates are now "commonly disputed or simply ignored by most archaeologists as being much too old to be real," Gruhn wrote.

Another study is also providing new evidence that modern humans may have arrived in North America much sooner. That study centered on evidence of human presence at 42 sites around North America, as well as the position of a land bridge that connected Siberia to Alaska.

The research, also reported in Nature, suggests humans may date back to at least a time known as the Last Glacial Maximum. During that period - from about 26,000 to 19,000 years ago and immediately thereafter - thick ice covered much of the continent.

The second study also pointed to humans as the cause of extinctions of many large Ice Age animals such as mammoths and camels.

I'm Pete Musto.

Words in This Story

flake(s) – n. a small, thin piece of something

blade(s) – n. the flat sharp part of a weapon or tool that is used for cutting

spear – n. a weapon that has a long straight handle and a sharp point

archeologist – n. a person who studies past human life and activities by studying the bones and tools of ancient people

diverse – adj. made up of people or things that are different from each other

anthropology – n. the study of human races, origins, societies, and cultures

extinction(s) – n. the state or situation that results when something, such as a plant or animal species, has died out completely