In the history of the Earth's life from scratch, to diversification, experienced up to hundreds of millions of years. For a more intuitive understanding of the evolutionary history of the Earth, the French scientist Reeve vividly 4.6 billion years compressed into one day: 1/4 before the time of the day, the Earth is in the clock points to 6:00, the lowest grade algae began to appear in the ocean, they are the longest until the 20:00, mollusks began activities in Oceanologia Et Limnologia 23:30, dinosaurs, but only "faceless" of a mere 10 minutes hurried on this day the final 20 minutes, mammals appeared, and quickly 23:50, primate ancestors debut in the final two minutes, their brains expanded three times, become human .
Reeve depicting the history of Earth is like a show, the various types of biological likened actor on the stage, which in turn stage, a wonderful interpretation and grand party. However, it was on stage, someone withdrew.
This is a long process, not just animals and plants reincarnation process, but also the birth of many species to extinction process. According to researchers fossil research, five times the Earth mass extinction and a number of smaller extinction events occurred at least. Perhaps many people will not understand, research on extinction of ancient times what practical significance? In the study of geology, there is an important way of thinking called "In the ancient theory this (future)," The ultimate goal is to understand the past in order to better understand the present and predict the future. If you know that our planet now also in a new round of mass extinction period, you will appreciate the genuineness of a sense of crisis.
Next, let us into ancient times, explore the mysteries of mass extinctions ......
1st: 440 million years ago glacial mass extinction
In the Ordovician period, shallow widespread on Earth, the climate is very suitable for biological growth, many marine organisms during this period, such as trilobites, crinoids, corals and nautilus etc.
However, to about 446 million years to 444 million years ago (ie, during the Late Ordovician) of 200 million years, the first mass extinction event took place on Earth, known as the "Ordovician extinction event." During the extinction event, about 85% of global species extinction, about 27% of families and 57% belong to extinction, from the number of extinct genus of view, the extinction of species ranked No. 3 in the fifth mass extinction event bit.
Paleontologists believe that this mass extinction was caused by the cooling of the global climate. Earth was going through the Andean - Saharan ice age, glaciers so large ocean currents and atmospheric circulation cooling, global temperatures drop, locked glacier water, causing sea level fall. These changes alter the biological habitat, coastal biosphere has been severely damaged, resulting in a large number of species extinction.
Zhidezhuyi that after the mass extinction soon, the Earth will enter the annals of the geological history of the Silurian period, and life on Earth has started to recover rapidly. Then those survivors is how to avoid catastrophe, the rebirth of it?
When in July 2005, of a geologist in Hangzhou, Zhejiang Yuhang District, Leshan geological resource survey, inadvertently on a cliff next to the pavilion only a few millimeters in diameter found in fossil shells. After continuous research, geologists found on this cliff a variety of fossil trilobites, crinoids, etc., and their survival between the age of 440 million years ago, belongs to the Ordovician and Silurian period. These tiny biological demonstrated during the Late Ordovician to Early Silurian biological evolution connection century. Experts in the late Ordovician, Silurian early century, Hangzhou is still in the low latitudes in the southern hemisphere, are deepwater area, while the original animals can only survive in shallow water. However, "natural selection, survival of the fittest", in the face of abnormal changes in the environment, only those who take the initiative to transform itself in order to gradually adapt to changes in the biological environment. They reduced the body to adapt to the deep sea environment, with special geographical environment in shallow water to deep water transition zone, and gradually migrate to the deep water, escaped the catastrophe, so that when the Hangzhou area as the late Ordovician mass extinction some of the survivors biological "sanctuary." So, someone guess: whether life on earth is in Hangzhou region had rarely left the seeds? Or say the least, at least this deep water area of Hangzhou was one of Silurian source of biological recovery blog.
2nd: marine life 375 million years ago, was hit in the mass extinction
Earth in the Devonian, many land rises above sea level and become land, paleogeography undergone great changes. This period ferns flourish, the rise of insects and amphibians, invertebrates into the rapid development period, the number of animals and fish species increased, modern fish began to appear, so Devonian often called "fish age."
However, 375 million years ago to 360 million years ago, Devonian to Carboniferous transitional period also there was a mass extinction, the incident lasted for about 1,500 years. There are many times during the peak of extinction, mass extinction of marine life, while the smaller terrestrial organisms affected. In terms of size, when 82% of the global extinction of marine species, almost all of the shallow coral extinction of deep-sea corals are also part of the extinction. The scale of the extinction event ranked No. 4 in 5 major extinction event.
About the reasons for the extinction event, some scholars believe that the end of the Ordovician similar, but also because of global cooling that the earth into the Karoo ice age some scholars believe that a comet colliding with Earth occurred during the event Others considered to be a large number of terrestrial plant breeding, they have evolved well-developed root depth of several meters below the surface soil, accelerated weathering terrestrial rock soil macronutrient released into surface water, resulting in water-eutrophication, hypoxia led to the seabed so that the mass extinction of marine species.
In 2010, an American scientist at Ohio University has proposed a new point of view. His study found that there is a natural nature species extinction process, new species will continue to replace the old species. The Late Devonian extinctions occur quantity and no significant increase in the number of very rare species only nascent, leading to sharply relative biological species extinction phenomenon occurs.
What does this mean? His view is that a large-scale invasion of species prevents the formation of new species, which led to extinction. Simply put, in the Devonian period, as the geological changes, sea-level change, land connected to each other, began to form terrestrial ecosystems, terrestrial amphibians began to move, some species have access to them had never lived surroundings. These budding species is invasive species, they flourish, to seize territory and resources, to prevent the generation of new species. Therefore, to prevent biological invasions, for today's biodiversity conservation is concerned, there is still an important reference.
3rd: 250 million years ago, a giant volcanic eruption caused mass extinction
In the Permian-Triassic transition period 250 million years ago, and so far the largest known extinction event a total of about 57 percent of the world's families, 83% of genera and species of marine life about 96% occur on Earth, and about 70% of terrestrial biological species extinct.
The extinction event and how did this happen? Recently, scientists at MIT and the CAS Nanjing Institute of Geology and Palaeontology found that the mass extinction event only experienced a short period of time 60,000 years, which for the entire history of the Earth, the only " blink of an eye. "
At that time, the frequent volcanic eruptions, ash deposited in the cover up all at the same time, but also for us to accurately record the scene at that time. Scientists have found that China Changxing County, Zhejiang Province Meishan section of stratigraphic section, clearly reflected the extinction process: in stratigraphic sections, more to the top of the formation, rugose corals, trilobites and other biological more scarce with the passage of time disappeared. Scientists are using carbon isotope analysis and other methods to determine the specific timing of these events, it was found Meishan section mark layer of volcanic ash mass extinction 25 million years ago began to 2.51941 ended at 2.51880 billion years ago, which means that mass extinction occurred about 60,000 years of this period, is a sudden extinction event.
At the same time, has been calculated, at the beginning of the biological mass extinction at that time, the earth's temperature is 25 , but to end at extinction, the Earth's temperature rose to 33 , within a short period of tens of thousands of years the Earth's temperature increased by 8 . Suffice it to say at the time the Earth experienced a global range of temperatures, temperature, drought, wildfires continue to burn out until the carbon dioxide concentration, marine life and also a large number of deaths due to hypoxia. Study the culprit, that was the massive volcanic activity, resulting in a large number of surface emissions of greenhouse gases and the greenhouse effect quickly.
4th: 208 million years ago, unexplained mass extinction
Dating back 200 million years ago in the Triassic to the Jurassic period of transition, the fourth mass extinction event on Earth, the impact of extinction throughout the land and sea, resulting in about 23% of global and 48 families % extinction of the genus, which ranked last in the size of five mass extinction events. It is also the extinction event, to provide a vast dinosaur living space, making Jurassic dinosaurs to become land animals advantage. The extinction event lasted very short, less than 1 million years, the reason has not yet been decided.
Views on the extinction of the most common is caused by a meteorite hit the Earth. France has a Rochechouart crater, geological age about 201 million years ago, this has been eroded crater diameter of about 25 kilometers, the original diameter may be about 50 kilometers, but some experts believe that this volume is insufficient cause mass extinctions. In 2013, Japanese scientists in the country near the coast Gifu Sakahogi rivers and tsukumi Oita Prefecture were found in a high concentration of osmium metal, the metal surface in the very rare, but it is abundant in meteorites. After isotope analysis confirmed that different osmium and surface newly discovered it exists osmium, which is the source of meteorites. They think that it is a diameter of 3.3 to 7.8 km of the meteorite hit the Earth caused by the strike led to the Triassic to Jurassic mass extinction.
In addition, there is a view that this incident was caused by the outbreak of large-scale climate change volcano related. In the Triassic period, a large number of volcanoes spewing lava and gases, changing the prevailing climatic conditions, carbon dioxide emissions from ocean acidification may also cause the extinction of marine and terrestrial organisms.
Fifth: the dinosaur era biological mass extinction 65 million years ago
February 15, 2013, a number of near-Earth asteroids 2012DA14 to position only 2.77 million km from Earth, the Earth's passing, although it does not hit Earth, but scientists really made to sweat. Because the asteroid about 44 meters in diameter, weighing up to 12 tons. If it hit Earth, the explosion will release the equivalent of 2.3 million tons equivalent of energy, almost shocked the world in 1908, the energy of the Russian Siberia Tunguska explosion.
However, our planet can not always be so lucky. Today, large and small craters on Earth hundreds, each one representing a traumatic year. The most famous one impact event, resulting in the first five mass extinction Earth, then the Earth's dominant dinosaurs unfortunately wiped out, and that is the Chicxulub meteorite impact event.
Dinosaurs are a class can support the body and hind legs to walk upright vertebrates, mostly inhabit the land, first appeared in the late Triassic about 225 million years ago, the dominant global terrestrial ecosystems over 160 million years, until about the late Cretaceous period 65 million years ago extinction. But the descendants of the dinosaurs - the birds survived, multiply so far.
The extinction of dinosaurs, scientists have proposed a variety of hypotheses, previously one of the more well-known are the following four: First, "says climate change." The hypothesis that the Earth 65 million years ago, climate change caused by a large number of plants and animals suddenly the other, "said geomagnetic changes." The hypothesis that the Earth's magnetic field when the sudden change caused a great number of animals being Third, the "acid rain says." The hypothesis that the late Cretaceous period on Earth possible through the strong acid rain, caused the extinction of dinosaurs Fourth, "said angiosperms poisoning." The hypothesis that the Earth angiosperms gradually replaced the gymnosperms later, after which contained toxins accumulate in food animals, leading to the extinction of dinosaurs. Of course, each of which has a scientific hypothesis side, but there are also controversial. Today, widely recognized by the international community is "meteorite impact theory."
The late 1970s, a Mingjiaogelun Penfield geologist engaged in oil exploration in Chicxulub Yucatan region of Mexico, the Yucatan Peninsula was surprised to find in the sea bed off the coast below, there is a 70 km diameter arc terrain. After his access to relevant information, found that there are one such arc terrain on the Yucatan Peninsula, the two actually can be synthesized in a complete circle, the diameter of the synthesized up to 180 kilometers across. However, because he is engaged in oil exploration work, this discovery did not attract his attention, which has nothing to do with the discovery of oil will not be published.
Later, there have been scientists in this new discovery, such as shocked quartz, gravity anomaly, glass and other meteorites proves this circular structure is formed by meteorite impact, but the impact body presumed diameter of at least 10 kilometers, from the impact energy equivalent 1014TNT equivalent, is the largest one in the world of all known bombing. Later, it was found that the formation of meteorite impact crater about 65 million years ago. With the deepening of the study, the scientists believe the Chicxulub meteorite impact event is the cause of the Cretaceous-Tertiary mass extinction of the dinosaurs.
Chicxulub impact event will be triggered massive tsunamis, earthquakes and volcanic eruptions, dust and debris from the impact will cause global turmoil, a long time obscured the sun, obstruct plant photosynthesis, resulting in the collapse of the ecosystem, a series of the disaster eventually led to about 17% of the world's families, 50% of genera, 75% of species extinction, scale extinction event ranked No. 2 in the fifth mass extinction event.
Glossary:
Osmium: 6th period of the Periodic Table group elements, platinum group metals, one of the members. Element symbol Os, atomic number 76, relative atomic mass 190.2, is a heavy platinum group metals, on earth densest material ever found in the world.
Shocked quartz: quartz or strike called by the earthquake quartz, is a micro-structure and different general quartz silica, formed only under very high pressure and temperature limited.
Gravity anomaly: Because Earth mass distribution irregularities caused by the gravitational field of gravity vector at each point and the number of normal gravity vector g poor. It is the study of the shape of the Earth, the Earth's internal structure and gravity surveys, as well as important data correction spacecraft orbit.
Tektites: silicon content high natural glass materials (average content of about 75% SiO 2). Its appearance is similar to obsidian on Earth, also known as "like obsidian", but the composition and structure of obsidian big difference.
(Author: Xi Cheng)
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