Scientists Want To Find Out Why Severe Extinction Happened Repeatedly?
Billions of years ago, there are more than billions of species on the earth, but now the number of existing species is just about millions. In other word, 99% species which once appeared on the earth were extinction. Extinction exists with the history of the mankind, no species can live forever and existing species would die away one day. According to scientific research, the main reasons of extinction are competition among different species, changes in the environment and other evolutionary factors.
Scientists used to think that Severe Extinction, species extinguished in a short period of time, just happened twice. But a recent research show that there are about 23 times of the Severe Extinction. It also shows a periodicity with occurring about every 2600 years. Scientists want to find out why Severe Extinction happened repeatedly?
Take the extinction of dinosaur for example, the reasons of dinosaur extinction given by scientists are climate change, volcanic eruptions and even other absurd suspicions. In 1980, the theory about dinosaur extinction, proposed by Louis Alpha Raz, was approbated by most people. Louis Alpha Raz, winner of the Nobel Prize in Physics in 1968, said the reason of dinosaur extinction was a hit between an unknown asteroid and the earth. Huge energy was released from this hit, with the equivalent energy of hundreds of thousands of atomic bombs, which led to the extinction. It sounds inconceivable, but Louis Alpha Raz gave proofs to support his theory. Rare elements of high concentration were found at terrane which formed at the time of Cretaceous and Miocene. As is known to all, rare elements are usually found in Meteorites, so this is a proof that a Meteorite may hit the earth in late Cretaceous period. Coincidentally, a crater, 180 km in diameter, was found in 1990 at the Yucatan peninsula in Mexico, which was, considered by scientists, formed because of this hit.
To explore the reasons of species extinction is undoubtedly a difficult work. When we try our best to find out the answers, we may be confused. Thinking from a different angle, we may discover the global ecosystem is in critical condition, the same to earth crust, forest and sand. Species extinction is the result of ordinary process of evolution and it is very natural.
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desribe the main classifications of meteorites?
how do astronomers believe these diffrent types of meteorites originated?
remaining debri of destroyed planets:
rock based - planetary crust and mantles
and metal based - planetary centra
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