New discoveries in Mexican caves advance the time humans entered the Americas by 10,000 years
The population growth of the Americas marks the massive expansion of humankind on the earth. Due to the earliest dating back, the Chiquivete Cave in Mexico occupies an important position in the study of human history in the Americas, and anthropologists have focused their attention here.
With the deepening of research, humans have reached some consensus on the claim that their ancestors came from the African continent. Archaeologists and geneticists have also drawn up their migration and spreading routes.
Previously, the mainstream view also believed that the history of humans entering the American continent was not long, but it was only 13,000 to 16,000 years old. But the exact time when humans first arrived in the Americas has always been a controversial topic. At least the exact time is still unclear.
However, in the recently published "Nature" magazine, two articles about when humans first entered the Americas have attracted worldwide attention. Their research has advanced the time when humans entered or occupied the Americas by at least 10,000 years. That is to say, the new research believes that modern humans inhabited and multiplied on the American continent about 30,000 years ago.
Of course, these two studies with more than 30 participants were not recognized by everyone, and there are still a lot of mysteries waiting to be solved in the research.
Gravel carbon dating data points to the history of human visits to the Americas 30,000 years ago
The population growth of the Americas marks the massive expansion of humankind on the earth. Among them, judging from the archaeological records of Mexico, it can be traced back to the earliest time and has an important position in the study of human history in the Americas.
Since 2012, the team led by Ciprien Adelain of the Autonomous University of Zacatecas, Mexico, has been conducting excavations in a cave called "Chiquivet" at an altitude of 2,740 meters in the Astiello Mountains in Mexico. . Here, they have discovered nearly 2,000 types of stone tools, of which 239 were buried in a deeper gravel layer. The carbon dating data of these gravel layers point to the historical indicator of 25,000 to 32,000 years.
Since the excavated tools are not many, Adelaine believes that this cave may be an occasional site visited by early humans, and was used as a shelter in the particularly cold winter. During the last ice age 26,000 years ago, North America was a place with harsh conditions. "There must be blizzards, hail and heavy snow." Adelaine said, and Chiquivert Cave is well insulated and can provide shelter for people who experience the snowstorm.
At the same time, Lorena Becerra-Valdivia and Thomas Hayam from Oxford University also set their sights on this cave. They combined the evidence of Chiquivert Cave with data from other archaeological sites in North America and the United States.
“Here, we use Bayesian age modeling methods to analyze the age data of 42 North American and Bering archaeological sites, and use the resulting age framework to clarify the temporal and spatial patterns of human transmission.” Higham said They combined these models with existing genetic and climatic evidence, and the data obtained indicated that humans may have appeared in the American continent during the last ice age between 19,000 and 26,500 years ago, but a wider occupation began. During the period of sudden warming, from 12,900 to 14,700 years ago.
Valdivia and Hiram also determined that the cultural traditions of Bellingen, Clovis, and Western origin are almost synchronized, and that these cultural traditions overlap with the time when the 18 now extinct animals finally appeared. This analysis also shows that the widespread human expansion in North America is also a key factor in the extinction of large terrestrial mammals.
Adelaine and his colleagues believe that the earliest date of modern man’s entry into the Americas can be traced back to 33,000 years ago, which is more than double the current popularity of about 16,000 years ago. The debate about entering the Americas adds a "flavor of gunpowder."
Uranium dating of mastodon remains shows that early humans came to America 130,000 years ago
However, there are still many questions about the time and way of human transmission.
In April 2017, "Nature" magazine reported a controversial study: A kind of "stone hammer" and a group of broken ivory teeth shaped by ancient humans were discovered in California, USA. These relics suggest that Homo sapiens may not The earliest humans to enter the Americas, the history of humans arriving in the Americas can be traced back to 130,000 years ago, 100,000 years earlier than previously thought.
Speaking of this discovery, we have to go back to 1992, when workers dug up the remains of a mastodon during the construction of a highway in southern California. It was about 3 meters tall and weighed 8 tons, which resembled an elephant. Of extinct animals. Archaeologists discovered at the site that there were severely broken rocks on the mastodon bones, which looked like they were used as hammers and anvils to break the bones to make bone tools or feed on bone marrow. At that time, there was no more reliable method to determine the exact age of the bones. It was not until 2012 that scientists used uranium dating technology.
They were surprised to find that these bones are 130,000 years old. A large number of previous studies have shown that Homo sapiens first arrived in the Americas through the Bering Strait nearly 20,000 years ago. The discovery of mastodon bones has pushed the history of mankind in the Americas almost 100,000 years ago.
A large number of studies also believe that during the last ice age, today’s Bering Strait was a huge ice sheet that connected Siberia and North America. Perhaps early humans migrated from Northeast Asia to the Americas at that time, and then settled in California. The southern part of the state has an archaeological site with a history of 130,000 years. However, due to the lack of the support of ancient DNA materials, it is impossible to confirm whether the ancient humans at that time made genetic contributions to the Native Americans.
Chris Stringer, a paleoanthropologist at the Natural History Museum in London, UK, is more inclined to believe that Denisovans or Neandertals were the first human ancestors to enter the Americas, because at least 100,000 years ago, they They have lived in southern Siberia, and there is no strong evidence to refute them from hiking from Siberia to Alaska.
Ancient DNA genetic data may reshape the history of the first inhabitants of the Americas
Over the years, scientists have integrated ancient and modern human DNA research and archaeological discoveries, and have basically reached a consensus on the origin of American Indians, that is, the time when humans crossed the Bering Strait to Alaska was about 20,000 years ago. The time in South America is about 14,000 to 15,000 years ago.
The remaining unresolved question is why it is assumed that at the entry point of the Bering Strait, the first human to expand south must pass through this area of central Mexico? Why is there no archaeological site of the same age as the Chikiwitte Cave found in the continental United States?
People use the coastal entry model to speculate that the earliest archaeological sites were submerged in offshore areas due to rising sea levels at the end of the last ice age. Within the continent, it may be necessary to determine and carefully investigate the appropriate age of geological or paleontological evidence, look for traces of human existence, and re-examine previous archaeological sites and excavated collections, and use new technology to find and identify human behavior. evidence.
The archaeologist and anthropologist François Lanoy of the University of Arizona in the United States believes that the latest discovery of the Chiquivete cave provides a good proof for the ancient human occupation of central Mexico. But he added that some of the data obtained from the cave is still difficult to give a reasonable explanation. For example, the stone tools may be moved into deeper strata due to geological changes or biological activities. "It may be that animals are digging the cave. Instead of moving stone tools by humans, making them look older than actual history."
Some archaeologists also believe that if they are indeed stone tools, you should be able to see traces of cleared chips on the edges, but there seems to be no clear evidence from the pictures in the paper.
As the first author, Adelaine also admitted that some tools may have been transferred to deeper strata, but the 239 oldest stone tools are buried under the impenetrable mud layer formed in the last ice age, so at least They are ancient. At the same time, he insisted that those flakes made of green crystalline limestone were man-made tools.
In addition to stone tools, the research team also tried to find other evidence of human existence. The corresponding author of the thesis and geneticists led by Esk Willerslev of the University of Copenhagen in Denmark once searched for the DNA of ancient humans in the mud of the cave, but they seemed to be out of luck and finally returned with nothing.
Archaeologist John Hoffker of the University of Colorado at Boulder said: “There is increasing evidence that human ancestors lived in the Americas 15,000 years ago, which allowed them to reach Mexico 20,000 or 30,000 years ago. Not surprisingly.” Early sites such as Chikiwitte Cave and Blue Fish Cave provide clear evidence of human activity, with artifacts dating back 24,000 years.
David Reich, a professor in the Department of Genetics at Harvard Medical School in the United States, is world-renowned for his research on ancient human genetics. The world’s top "paleogenome factory" established by him has collected more than 7,000 ancient human genome data, accounting for the world's total The Americas is also the focus of its research. Reich said that in addition to archaeological evidence, it is necessary to dig deep into ancient human genetic evidence to provide a more convincing answer to when humans first arrived in the Americas.
Our reporter Zhao Hanbin