Encyclopedia knowledge: how many species have humans extinct?

In the past century, the extinction rate of species under human intervention was faster than that of nature 1000 times.

There are 75 species extinct every day and 3 species extinct every hour in the world.

Many species disappeared from the earth before they were described and named by scientists.

A research team led by Jeremy Thomas of the British Center for Ecology and Hydrology reported in the recently published Science magazine that in the past 40 years, the species of native birds in Britain have decreased by 54%, the species of native wild plants by 28% and the species of native butterflies by 7 1%. Insects, which have always been considered to have a large number of species and strong adaptability, are also facing extinction.

Scientists infer that the earth is facing the sixth mass extinction. Dr. Jiang Zhigang, chief researcher of Institute of Zoology, Chinese Academy of Sciences and executive deputy director of China Endangered Species Science Committee, also believes that from the perspective of nature conservation biology, since the industrial revolution, the earth has entered the sixth extinction period.

If we extend the butterfly survey to other insects in Britain and invertebrates on the whole earth, we are obviously facing a serious biodiversity crisis.

A species refers to a natural group of individuals who can mate with each other and produce fertile offspring. Extinct species are those that have not been clearly found in the wild in the past 50 years. "Mass extinction is not only the extinction of one species, but the extinction of many species in a relatively short geological history, that is, hundreds of thousands or millions of years." Dr Jiang Zhigang said.

British scientists analyzed the survey data of birds, plants and butterflies in Britain in the past 40 years and found that the number of these insects decreased on a large scale. Moreover, it is worrying that this phenomenon of large-scale population decline occurs in all major ecosystems, all over Britain, rather than concentrated in a few areas with serious ecological deterioration. Thomas said: "Insect species account for more than 50% of the global species, so their mass extinction is bad news for the biodiversity of the earth."

Since the industrial revolution, many species have appeared on the earth, such as great auk, North American passenger pigeon, South African spotted donkey, Bali Lake in Indonesia, Australian marsupial, Zhili macaque, Alpine antelope, Platts wild horse, Taiwan clouded leopard and so on. According to the Red List of Endangered Species published by IUCN, there are still 1/4 species of mammals, 1.200 species of birds and 30,000 species of plants in the world at present.

Since multicellular organisms were born on the earth 600 million years ago, there have been five mass extinctions.

The first mass extinction on the earth occurred at the end of Ordovician 440 million years ago, and about 85% of the species became extinct.

About 365 million years ago, in the late Devonian, the second extinction occurred, and marine life suffered heavy losses. The third extinction occurred at the end of Permian about 250 million years ago, which was the largest and most serious in the history of the earth. It is estimated that 96% of species on the earth are extinct, including 90% of marine life and 70% of terrestrial vertebrates.

The fourth time happened 65438+85 million years ago, and 80% of reptiles became extinct. The fifth time happened in the Cretaceous period 65 million years ago, which is also a well-known one. The dinosaurs that ruled the earth for 65.438+600 million years became extinct.

Dr Jiang Zhigang explained that the first five mass extinctions were mainly caused by geological disasters and climate change. For example, the first mass extinction was caused by global climate cooling, and the one that happened at the end of Cretaceous was that an asteroid hit the earth and caused the global ecosystem to collapse.

At present, the sixth mass extinction is going on, and human beings have become the culprit. Experts believe that it is difficult to say whether humans will be included.

Dr Jiang Zhigang does not deny that species extinction is a natural law from an evolutionary point of view. For example, the giant panda population is currently in decline. However, since the emergence of mankind, especially since the industrial revolution, the population of the earth has been increasing and more and more means of subsistence are needed. The scope of human activities is getting bigger and bigger, and there are more and more disturbances to nature. In this way, a large number of forests, grasslands and rivers disappeared and were replaced by roads, farmland and reservoirs ... The natural habitat of living things was fragmented by traces of human activities. "Every road is an insurmountable obstacle for animals. Even the butterfly populations distributed on both sides of the road are isolated and no longer fly around for gene exchange as before. " Dr. Jiang Zhigang said sadly, "Not to mention the large animals such as Tibetan antelope, lion and tiger."

Some scientists estimate that in the past 200 million years, 90 species of vertebrates have become extinct every 100 years, and one higher plant has become extinct every 27 years. However, due to human interference, the extinction rate of birds and mammals increased by 1000 times, reaching1000 times.

Stuart Pim, a famous biologist at Duke University in the United States, believes that if species decrease at this rate, by 2050, a quarter to half of the existing species will be extinct or endangered.

Existing species are decreasing, but it is difficult to produce new species.

According to the fossil record, after each extinction, some new advanced groups were replaced. The rapid reproduction of mammals after the extinction of dinosaurs is a typical example.

But Dr. Jiang Zhigang believes that creatures are always evolving, and all the creatures we see now have evolved over a long period of time. So it takes a long time and a lot of space to produce new species. But now, under the management of people everywhere, the natural environment is getting worse and worse, and organisms have lost the environment and conditions for natural evolution. Species are constantly dying out naturally, but it is difficult to produce new species.

Just like a tiger, if it is given enough living space to hunt freely, it may evolve and produce a new species similar to a tiger, but now it is difficult for it to survive, let alone evolve.

The surface of the earth is a huge biosphere composed of all biological species such as animals, plants and microorganisms and their living environment, and human beings are one of them. A large number of creatures disappeared in the sixth extinction, but it is difficult to produce new species like the first five. The earth's ecosystem is far more fragile than we thought. When it is damaged to a certain extent, it will lead to the collapse of the system on which we live.

If the last moment doomed by human actions comes, will human beings become survivors?

65 million years ago, after the asteroid hit the earth, the sulfur dioxide, carbon dioxide, rock fragments and dust formed by the impact soared into the sky, covering the whole earth, and also caused a large number of volcanic eruptions, and the temperature of the earth rose sharply in a short time.

A few years after the impact, sulfur dioxide in the stratosphere attached to the dust, forming sulfuric acid droplets, covering the whole earth and blocking the sun. The photosynthesis ability of surface plants is greatly weakened, and the temperature drops sharply. Dinosaurs couldn't adapt to the bad climate and began to die.

A large amount of salt evaporation may have destroyed the ozone layer that protects the earth. Volcanic eruption on the surface of the earth caused plants to wither, acid rain formed by sulfuric acid droplets in the sky, and cruel winter killed more dinosaurs.

The winter has finally passed, and the sun can shine on the earth again. However, a large amount of carbon dioxide in the atmosphere led to a strong greenhouse effect, and the temperature of the earth began to rise sharply. The dinosaurs that once ruled the earth for 65.438+0.6 billion years finally became extinct.

background information

According to the statistics of the State Environmental Protection Administration, six kinds of large mammals were extinct in China in the 20th century: Platts wild horse (1947), alpine antelope (1920), Xinjiang tiger (19 16) and China rhinoceros with one-horned horn (65438).

There are 1000 rare and endangered species, 28 extremely endangered species and 7 extinct or possibly extinct species in China. Among gymnosperms, 63 species are endangered, 14 species are extremely endangered, and 1 species is extinct. 433 species of vertebrates are threatened, and 10 species are extinct or may be extinct.