In geological history, a period of large-scale glacial activities occurred in cold climates, called the ice age, and the ice age. There were three times this ice age, namely the late Precambrian period, the Carboniferous-Permian period and the Quaternary period. When the Quaternary Ice Age came, the annual average temperature on the earth was 10℃~15℃ lower than the present. More than one-third of the continents in the world are covered with ice and snow, with an area of ​​52 million square kilometers and a thickness of 100 ice.

About 0 meters, sea level drops by 130 meters. The Quaternary Ice Age was divided into 4 ice periods and 3 interglacial periods. During the Interglacial period, the climate warms up, sea level rises, and the earth regains its vitality. The Quaternary Ice Age has the most relics, such as the fjords of the Scandinavian Peninsula, the numerous moraine hills in Northern Europe, Central Europe, and North America, the U-shaped valleys and steep peaks in the Alps, and the huge ice brisks in the Jurass Mountains at the junction of France and Switzerland, which are all products left by the action of Quaternary glaciers.

[Edit this section] Definition of ice age

The ice age can be divided into broad and narrow meanings. The ice age in the broad sense is also called the ice age. The ice age in the narrow sense refers to the ice age that is one level lower than the ice age. The ice age refers to the geological period on the earth with cold climate, thickening polar ice sheets, and wide spreading, and sometimes strong glacier effects in medium and low latitude areas. The colder period in the ice age is called the ice age, and the warmer period is called the interglacial period. The ice age, the ice age and the interglacial period are both geological time units divided according to climate. The duration of the ice age is equivalent to the geological age unit or greater than the genus. The time interval between the two ice ages can be several centuries. According to statistics, the occurrence of the ice age period has a period of 150 million years. The duration of the ice age is equivalent to the period of geological age units.

In the billion years of geological history, there have been at least three major ice ages around the world. It is recognized that the Great Ice Age in the late Precambrian period, the Carboniferous-Permian Great Ice Age and the Quaternary Great Ice Age. In areas where glaciers have been active, the remaining moraines are the main objects of glacier research. The moraine layer of the Quaternary Ice Age is the most complete, widely distributed, and the most detailed study. During the Quaternary, according to the changes in the glacier coverage area, it can be divided into several ice ages and interglacial periods. The ice cover areas account for about 30% of the land surface area respectively.

and 10%. However, the glacier development level in the ice ages of each continent varies greatly. For example, the ice sheet on the European continent once reached 48° north latitude, while Asia only reached 60° north latitude. Due to the differences in climate change with regions and research methods, the division of ice ages varies in different regions. In 1909, A. Penke and E. Bruckner of Germany studied Quaternary glacier deposition in the Alps and divided and named 4 ice periods and 3 interglacial periods. Subsequently, corresponding ice periods and interglacial periods were also divided around the world.

[Edit this section] Causes of the Ice Age

There are various arguments about the cause of the Great Ice Age, but many researchers believe that it may be related to the solar system's cycle in the Milky Way. Some believe that the sun has the smallest luminosity when it reaches the near-glacial center point, which makes the planets cool and form the Great Ice Age on Earth; some believe that the material distribution in the Milky Way is uneven. When the sun passes through areas with high interstellar material density, it reduces the sun's radiation energy and forms the Great Ice Age on Earth.

The melting of the Antarctic ice sheet caused a large amount of fresh water to be injected into the ocean, and the concentration of seawater was reduced. The "ocean conveyor belt" gradually stopped: the warm current cannot reach cold seas; the cold current cannot reach warm seas. Global temperatures decreased, and another ice age was coming. Most of the northern hemisphere was frozen.

Experts say non-human or disease has caused it to disappear ten thousand years ago

[Edit this section]Flora and flora characteristics

During the Ice Age ten thousand years ago, the North American continent was full of giant beasts, such as long-haired mammoths, sharp-toothed mastodons, felines with saber-toothed feathers and giant bears. But over thousands of years, these giant beasts have become extinct. Many experts believe that humans killed these giant beasts. Last August, our newspaper also reported on the title "Humans destroyed the Ice Age Behemoth?". However, the authoritative magazine "Nature" published on May 11 published a new research report, which said that the extinction of giant beasts 10,000 years ago was caused by climate change rather than humans or diseases.

Human camps do not have mammoths and wild horse corpses

Fossils of the corpse show that humans are keen on hunting bison and moose, but they all survived

Scientists such as Dale Guthre from the University of Alaska dated 600 American bisons, moose, elk, mammoth, wild horses and human bones from 18,000 to 9,000 years ago, and found that before human footprints set foot on Alaska and now the Yukon region of Canada, the number of mammoths and wild horses was declining sharply. However, at the same time, the number of bisons existed in large quantities, and the number of moose and elk was also increasing sharply. If humans over-hunting led to the extinction of giant beasts, they should first catch small deer. Why did bisons exist in large quantities, while moose and elk increase sharply?

A more interesting discovery is that fossil records show that humans are more keen on killing bison and moose, but they survived. "I imagine that humans can hunt any animal they can kill. But the human camps do not have any mamma and wild horse corpses, on the contrary, there are only a lot of remains of bison and elk."

The reason for the extinction of giant beasts such as mammoths and wild horses is that they cannot find enough food due to the warming climate. The preserved pollen samples indicate that climate changes have caused changes in the nutritional supply of these animals. Scientists from the University of Canada and Alaska believe that from the Pleistocene to the Holocene, that is, the late Pleistocene, the climate changed from cold and drought to warm and humid, and the dwarf grass grew more lush, and then forests appeared. The giant beasts such as mammoths and wild horses that survived well in cold climates cannot adapt to the new climate. Because mammoths and Latin American horses cannot find enough food from the forest, they did not survive. "A long time ago, the number of bison and elk increased greatly. The only reasonable explanation is that the latter has a large source of food."

Antiochlee also said that the fossil record has caused doubts about the extinction of a great plague. Scientists have believed that fatal diseases would cause all species to become extinct, but this is not reflected in the fossil record. And diseases that can contend and cause deaths of multiple species are very rare, and bison, elk and moose are not affected, so it can be inferred that this assumption is not valid.

[Edit this section] Expert opinion

Some problems are difficult to solve at present

Although there is currently no sufficient evidence to prove the true cause of the extinction of behemoths, many evidences suggest that the cause of extinction of large animals in Pleistocene is more likely to be a common result of human and climatic factors rather than simply belonging to one of them. However, to prove this, we also need to know when the population of each continent has increased to a point that is sufficient to affect the extinction of large animals, and to determine how climate parameters change will affect the number range of animals hunted. To understand this, fungal spores in large animal feces in lake deposits need to be studied, and DNA is used to simulate the changes in the number range of large animals. In order to more detailed understanding of whether the last ice age conversion is different from the early ice age conversion, it is necessary to improve the level of chronological research and reconstruct the paleoclimates of South America and Africa.

Disputes among all parties

The new conclusion sparked three major controversies

However, the new conclusions did not reach a consensus. Some scientists are cautious about the research, believing that mammoths may die from climate change in Alaska and Yukon, but in other parts of the continent, human indiscriminate killing is still the main cause of the extinction of mammoths.

1. Human hunting theory

Some scientists believe that the first time humans entered the North American continent from Siberia was about 12,000 years ago, while the mammoth and wild horses died roughly between 11,500 years ago and 12,500 years ago, and the two coincided exactly. Therefore, some scientists inferred that hungry humans over-hunting these mammals led to their extinction.

They believe that if climate change is the main factor leading to the extinction of behemoths, then the extinction time of behemoths around the world should be consistent, because the impact of climate change on the world is the same. However, the extinction time of behemoths in different places is different, which shows that only the time when humans migrate to various places can be reasonably explained. David Steman, a researcher at the University of Florida, said that temperature changes play a very important role in the process of biological extinction. However, many animal species are more vulnerable to human attacks, and the threat to humans is even much greater than that of climate change.

2. Disease extinction

Some scientists believe that the climate change theory view is difficult to explain a fact: in the previous climate change, sometimes the climate changed violently, and the mammoth was not extinct. Obviously, climate change is not the only reason. At the same time, the human hunting theory is difficult to establish. Because archaeological discoveries show that there are few traces of human activities in the gathering places of mammoth. On the other hand, at that time (11,000 years ago), human hunting tools were extremely simple, mainly relying on stone tools, and it was quite risky to round up huge and strong mammoths.

A research paper in the journal Molecular Biology and Evolution in February pointed out that scientists found viral DNA on the gene fragments of mammoths, which belongs to an endogenous retrovirus. This virus has undergone thousands of years of reproduction, evolution, and still survives, indicating that it has an important impact on the gene chromosomes of organisms. This discovery supports the theory of disease extinction.

Three, comprehensive factor theory

Some scientists have obtained evidence from simulation experiments, chronology, archaeology, paleontology, and ecology to prove that the cause of extinction of large fauna in Pleistocene should be attributed to the combined effect of human factors and climatic factors. They believe that it is too simple to think that humans begin to appear and their hunting activities are the cause of extinction of some large fauna. In fact, there is evidence that the debate that overhunting (in a narrow sense) is the cause of extinction of large fauna does not apply to Western Europe, Siberia and Alaska, nor even to Australia and central North America. Without the climate change of the late Pleistocene, despite the emergence of humans, Alaska horse herds, Eurasian mammoths and Irish deer might have survived for a longer time.

Recent data have shown that humans accelerated the extinction of large fauna. But at the same time, humans played a certain role in climate change during the late Pleistocene.

In the history of Earth's climate change, ice ages and interglacial periods have always appeared alternately, adding and decreasing clothes for the Earth. So when will the next ice age come? Due to the result of people releasing a large amount of carbon dioxide into the air, the earth has an unprecedented state in history. Therefore, some scientists boldly predict that the ice age may never come back.
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