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The oldest stone tools out of Africa have been discovered in western China, scientists reported Wednesday. Made by former members of the human lineage, called hominids, the chipped rocks are estimated at 2.1 million years old.
The discovery could add a new chapter to the evolutionary history of the hominin, suggesting that some of these species have left Africa much earlier than expected and have succeeded to travel more than 8000 miles east of their place of birth.
The age of Chinese tools suggests that the hominers who made them were neither big nor big brains. Instead, they could be little biped monkeys, with brains the size of a chimpanzee.
"The implications of all this are great," said Michael Petraglia, a paleoanthropologist at the Max Planck Institute for the Science of Human History, who was not involved in the new study. "We need to re-evaluate our understanding of human prehistory in Eurasia."
The human lineage appeared in Africa; the ancestors of modern humans have separated from those of chimpanzees more than seven million years ago. But scientists have known for many years that Asia has a long human history.
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In 1891, the Dutch explorer Eugene Dubois discovers in Indonesia a human skull of about half a million dollars. # 39; years. Later, paleoanthropologists named Dubois' skull, Homo erectus, a species that was later found on many other sites in Asia; some specimens were as old as 1.6 million years old.
Asian fossils have shown that these hominins were about as tall as living humans and had enough big brains. While chimpanzees have a brain about one-third of our size, Homo erectus had a brain about two-thirds of its size.
In Africa, paleoanthropologists discovered an even longer fossil record of hominids. The oldest still found date back more than six million years.
The first hominids could walk on two legs, but they were short and had only brains the size of a chimpanzee. 1.9 million years ago, Homo erectus or a close relative crossed East Africa.
Many paleoanthropologists have come to badume that Homo erectus were the first migrants to leave Africa. But this image became blurred in the 1990s, while other hominid bones were discovered in other parts of Asia.
In Dmanisi, Georgia, scientists discovered remarkably ancient fossils, some as old as 1.75 million years old. Some stone tools found there seemed to be even older: 1.82 million years old.
Hominids of Dmanisi did not look much like Homo erectus: they were small and had tiny brains.
In China, researchers have also found evidence of early occupation of the hominin. In 1964, researchers uncovered a skull of Homo erectus in a western county called Lantian. According to preliminary estimates, there are 1.15 million years.
But in 2001, Zhaoyu Zhu, a geologist from the Chinese Academy of Science in Guangzhou, and his colleagues began to take a fresh look at the fossil site. They determined that Lantian's skull was actually much older: 1.63 million years old.
In their investigations of the area around the fossil, Dr. Zhu and his colleagues also discovered what looked like old built-stone tools 200 feet deep in the side of one's body. ravine.
The researchers decided on a thorough search of the ravine, climbing up the steep slope to search for more artifacts. "Working up and down can sometimes be overwhelming," said Robin Dennell, a paleoanthropologist from Exeter University who joined Dr. Zhu's team in 2010.
The risk bearing fruit. The researchers found more than a hundred stone tools embedded in 17 geologic layers of the ravine.
But it was painstakingly slow work because the researchers wanted to convincingly demonstrate that it was well made tools by hominans – and that they were really old.
"We wanted to make it watertight and bombproof," said Dr. Dennell
. In the new study, he and his colleagues argue that the stones could not be damaged naturally. The surrounding rock was formed from a grbadland soil, which contained no stone-sized tools and shape.
Instead, the researchers claim that Lantian hominids had to travel for miles to mountain streams to find the right stones to make tools. The hominids carried the tools with them to harvest food, perhaps using sharp stones to cut meat from the carcbades.
To determine the age of tools, researchers took advantage of the changing magnetic field of the planet.
From time to time, the Earth's magnetic field swings, turning from north to south. Magnetic minerals in the soil and the ocean are pushed in alignment with the field; when they are trapped in the rocks, they always point in the direction of revelation.
Geophysicists have accurately determined the timing of these magnetic flips, which occurred at the same time all over the world. This is a useful way to date the material found in the rock layers.
The layers in the ravine have formed over several hundred thousand years. And the oldest tools were carefully sandwiched between the rocks that formed between two magnetic field rockers: 2.14 million years ago, and a second there are about 1.85 million d & # 39; years.
Dennell and his colleagues estimate that the tools are close to the end of this window: 2.12 million years. This would make these tools the oldest evidence of hominids ever found outside of Africa.
And this makes it unlikely that the first hominids to spread out of Africa were Homo erectus. Instead, speculated Dr. Dennell, a much older branch of the human tree has ventured.
The trigger for this migration? Maybe it was finding how to make sharp stone tools.
"Suddenly, you had a primate that could get meat from a carcbad, and that opened up a new world for them," says Dr. Dennell. "This simple technology was enough to get them out of Africa and all over Asia."
Rick Potts, director of the Smithsonian Institution's Human Origins program, found this new study compelling, proving that the stones were good tools and that they were extremely old. "I think they have it," he said. However, Potts did not think that Lantian hominids were small and small. Instead, he speculated that there are fossils similar to Homo erectus over 2.1 million years old that are waiting to be discovered in Africa.
But John J. Shea, paleoanthropologist at Stony Brook University, is not yet convinced of the stones. At the very least, he argued, Dr. Dennell and his colleagues should make a statistical comparison between these supposed tools and naturally damaged rocks.
And Dr. Shea is wary of relying solely on tools to prove that the hominids were in Asia over two million years ago.
"Bottom line – no fossils of hominids, not hominids," he says.
Since paleoanthropologists have already found a 1.63 million – year – old skull in Lantian Province, Dr. Dennell said that it was possible for researchers to find a fossil of L million an [[[[[[mucholderhomininhidingbesidethetools
"Remember, it will take time," he said. "But it will be worth watching."
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