I.eMass extinction。Biomass extinction refers to the sudden death of a large number of organisms in more than one geographical area in a relatively short geological period, resulting in a sudden and sharp decline in the number of biological species in a short time.[1]
The extinction and rebirth of living things are natural phenomena in the evolution of life, which occur almost every moment.The existing statistical data show that the life on the earth is dying out at an average rate of 2-5 families every 1 million years;There were 1 billion to 4 billion kinds of animals, plants and fungi on the earth, of which more than 97% have been extinct.
Global extinction
Announce
edit
In the whole life history, biological replacement occurs at an uneven speed.At least 22 times in 540 million years since PhanerozoicExtinctionEvents with global impactMass extinctionThe following five times.
The Ordovician Silurian mass extinction occurred 440 million years ago, consisting of two episodes, which are separated by 500000 to 1 million years.The first scene is that many creatures living in warm shallow sea or deeper sea have become extinct. The extinct genera account for 60%~70% of the total genera at that time, and the number of extinct species is as high as 80%.The second act is that those living in the colder waters that survived the extinction event in the first act were destroyed.
Late DevonianMass extinctionOccurred 375 million years ago, its extinct families accounted for 30% of the total families at that time, and more than 70 families of marine animals were extinct. Terrestrial organisms also suffered heavy damage.The extinction event lasted for a long time, was large in scale and affected many categories.
Late Permian organismsCluster extinctionIt happened 252 million years ago.It was the largest of the five mass extinctions, resulting in the disappearance of about 70% of the families of terrestrial organisms and 95% of the species of marine organisms, and the extinction of trilobites, tetracorals, bedstead corals, super foraminifera, and crinoids, which flourished in the early Paleozoic, and the overall collapse of the reef ecosystemImmobilized biological communities quickly withdrew from the stage of history.
Late Triassic organismCluster extinctionIt happened 208 million years ago.Although the impact of cluster extinction at the end of Triassic is relatively slight, which is the weakest of the five cluster extinction, there are also 1/3 of the family extinctions.
At the end of the Cretaceous, the mass extinction of organisms occurred 65.5 million years ago, marking the end of the Mesozoic Era.About 26% of the families, more than half of the genera and 75% of the species disappeared in this mass extinction.This mass extinction event has impacted the marine and terrestrial ecosystems, and since then, the biological appearance of the Cenozoic has changed.
Is human being in the sixth mass extinction
The sixth mass extinction may have begun in the Neolithic Age 11000 years ago, when humans had better tools to hunt wild animals more easily.Since more than 200 years agoindustrial revolutionSince the beginning of the era, human productivity has advanced by leaps and bounds. A large number of forests have been cut down, a large number of wild animals have been hunted, a large number of mines have been mined, a large number of waste gases and wastes from factories have been discharged, and the earth's ecological environment has been greatly damaged.
There are more than 5000 known living mammals, but 1/4 of them may be extinct;At present, 1211 bird species are endangered, accounting for 1/8 of the total;The world's endangered plant species account for 47% of all species!In the past period of mass extinction, on average, only a few species were extinct every day, but now the number of extinct species has soared to 100 every day. If this is calculated, 3.65 million species will be extinct within 100 years.If there are 20 million species of living things in the world, the species on the earth will disappear in 1000 years.andExtinction of speciesThe rate of extinction of three species per year is nearly 10000 times faster than that of the prehistoric normal situation, and 1 million times faster than that of the formation of new species, which is far faster than any prehistoric mass extinction.Therefore, in a sense, it may not be too much to call it the sixth cluster extinction.
However, some scholars believe that human understanding of today's biodiversity on the earth is far from enough, and the short history of human beings has not been able to feel the whole process of the extinction of life clusters, not to mention the ability of nature to regulate itself is far stronger than human understanding.It seems that there is insufficient evidence to assert that the sixth cluster extinction is taking place.[2]
The "culprit" of mass extinction
The reasons for mass extinction of organisms are complex and diverse, and the reasons for each mass extinction are different.It is generally believed that climate change and its related events caused two episodes of Ordovician SilurianExtinctionThe main reason for.The mass extinction at the end of Devonian is a global cooling event similar to that at the end of Ordovician, which is believed by some people.The comet impact event may be the cause of the extinction of the cluster.At the end of the Permian, the mass extinction was the result of the joint action of large-scale underground magmatic activity, which caused the surface methane release and volcanic eruption.The end of Triassic mass extinction occurred against the background of long-term climate change, rapid sea level fluctuations, and disasters both inside and outside the earth.Asteroid impact theory is widely accepted as the main factor that caused the extinction of Cretaceous organisms, but there are also other different views.
In addition, the large radiation of living things is closely related to the mass extinction. When the mass extinction of living things occurs, not all the living things on the earth are extinct, but some living things with strong adaptability or where the environment is not seriously deteriorated will survive and pass through the survival period.In the mass extinction, most of them are less adaptable and primitive creatures.When they withdraw from the stage of history, they create a living space for more adaptable and progressive creatures.When the earth's ecological environment starts to improve, such creatures will quickly become active and occupy the space left by extinct creatures.At the same time, many new species will appear in the new environment, making the biological world gradually enter a period of great development, which is the so-called biological radiation.[2]
Meet conditions
Announce
edit
There are four conditions for mass extinction:
Magnitude: the extinction value with substantial significance.
Breadth: It has a global breadth.
Range: involving a wide range of different taxons.
Intermittent: limited to relatively short geological interval.[3]
Causes and consequences
Announce
edit
There are many reasons for the extinction of biological swarms, such as extraterrestrial collision, volcanic activity, climate cooling or warming, transgression or regression (sea level rise or fall) and hypoxia.Every major extinction event can cause more than 80% - 90%Extinction of species。However, a few species with strong vitality or escape ability can endure the extremely harsh environment caused by the disaster, or escape from the disaster area to other places for refuge and survive.At the same time, environmental changes caused by disasters have also created conditions and opportunities for the birth of new species.The surviving and newly born species during the mass extinction began to recover and develop after the extinction event, and thus created a new chapter in biological evolution. Therefore, every global extinction event is accompanied by the recovery and development of organisms.
classification
Announce
edit
According to fossil records, there have been five major mass extinction events of biological groups in geological history, namely, mass extinction in the end of Ordovician, Devonian, Permian, Triassic and Cretaceous.CretaceousThe extinction event attracted attention because of the extinction of dinosaurs, but the Permian extinction event was the largest one with the most biological groups involved and the most far-reaching impact.
The first mass extinction occurred at the end of the Ordovician period 440 million years ago, resulting in the extinction of about 80% of the species.
The second timeMass extinctionOccurred in the late Devonian period about 365 million years ago, marine organisms suffered from the disaster of extinction.Devonian is the age of fish. Devonian is a period of great changes in the biological world of the earth. The large-scale march from ocean to land is the most prominent and important biological evolution event in this period.
The third and most serious mass extinction occurred at the end of the Permian period about 250 million years ago, leading to more than 95% of the earth's biological extinction.In the late Permian, the largest and most far-reaching biological mass extinction event occurred in the global geological history.Trilobites, tetracorals, transverse corals, fly foraminifera and crinoids, which flourished in the early Paleozoic era, were all extinct, and brachiopods, ammonites, echinoderms and bryozoans were also severely hit.Amphibians flourished in a large number in the Permian period, with the common euodontoid salamanders. Reptiles continued to develop, and warm blooded reptiles, theropods, pioneers of mammals, also began to develop.
The fourth extinction occurred in the late Triassic 200 million years ago, and reptiles suffered heavy damage.Triassic is the period of the rise of reptiles and gymnosperms, and the first period of Mesozoic.
The fifth mass extinction occurred in the Cretaceous period 63 million years ago. Scientists believe that it was caused by an asteroid hitting the earth. Since then, the dinosaurs that ruled the earth for a long time disappeared from the earth, withdrew from the stage of history, and mammals began to appear.[3]
influence
Announce
edit
In the past 100 years, human beings have destroyed the environment and abused natural resources, resulting in a sharp decline in species in the world.Since the emergence of human beings, especially after the industrial revolution, human beings have only paid attention to the practical value of specific biological sources and developed them wantonly, ignoring the indirect and potential value of biological diversity, so that the Earth's life support system has been mercilessly eroded by human beings.Scientists estimate that in the past 200 million years, 90 vertebrates and one higher plant would be extinct every 100 years and 27 years on average, respectively, without human interference.In this context, human interference has increased the extinction rate of birds and mammals by 100 to 1000 times.Since 1600 years ago, 724 species of recorded higher animals and plants have been extinct.The vast majority of species have been extinct before humans knew it.The earth is experiencing the sixth time that human destruction of the environment is the main causeMass extinction。
