VOA科学技术2023--Study: Footprints in New Mexico May Be Oldest Sign of Humans

Study: Footprints in New Mexico May Be Oldest Sign of Humans

New research confirms that a fossil¹ 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 remains² 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 pollen³ and quartz⁴ 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 skeptical⁵ 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 Geological⁶ 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 genes⁷ 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 ambiguous⁸."

Words in This Story

fossil – n. something (such as a leaf, skeleton⁹, 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

1 fossil   

n.化石，食古不化的人，老顽固

参考例句：

• At this distance of time it is difficult to date the fossil.时间隔得这么久了，很难确定这化石的年代。
• The man is a fossil.那人是个老顽固。

2 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

3 pollen   

n.[植]花粉

参考例句：

• Hummingbirds have discovered that nectar and pollen are very nutritious.蜂鸟发现花蜜和花粉是很有营养的。
• He developed an allergy to pollen.他对花粉过敏。

4 quartz   

n.石英

参考例句：

• There is a great deal quartz in those mountains.那些山里蕴藏着大量石英。
• The quartz watch keeps good time.石英表走时准。

5 skeptical   

adj.怀疑的，多疑的

参考例句：

• Others here are more skeptical about the chances for justice being done.这里的其他人更为怀疑正义能否得到伸张。
• Her look was skeptical and resigned.她的表情是将信将疑而又无可奈何。

6 geological   

adj.地质（学）的

参考例句：

• aeons of geological history 数以亿万年计的地质史
• The workers skirted the edge of the cliff on a geological survey. 工人们沿着崖壁作了一次地质勘察。 来自《简明英汉词典》

7 genes   

n.基因( gene的名词复数 )

参考例句：

• You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因，所以能够活得很长。 来自《简明英汉词典》
• Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪

8 ambiguous   

adj.引起歧义的，模棱两可的，含糊不清的

参考例句：

• This sentence is ambiguous in sense.这个句子意思不清楚。
• The title of this chapter is ambiguous.这一章的标题含义模糊。

9 skeleton   

n.骨骼，框架，骨干，梗概，提要

参考例句：

• A long illness made a skeleton out of him.长期的卧病使他骨瘦如柴。
• Her notes gave us just the bare skeleton of her theory.她的笔记只给我们提供了她的理论的梗概。