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Go back to: Challenges | Next Section: Endangered SpeciesAll species die and disappear someday. This is known as extinction. In most cases, extinction is a means by which a new species arises. There is debate over the pace of extinction. Generally, there are two large types of extinction. This is also known as natural extinction. Background extinction refers to the extinction that occurs naturally in the evolution process. 0.00003% of species become extinct naturally according to fossil records. This extinction has been occurring since the origin of life on earth. During the ecological process, the natural extinction occurs following the evolution of the species. If a species cannot succeed in adapting to its surroundings it eventually becomes extinct. Factors of background extinction include gradual changes in temperature, humidity, predator-prey relationships , and tectonic plate movements. David Raup estimates that the average species stays around for 4 -22million years before it becomes extinct and that 99.9 of all the species that have ever existed are now extinct. In mass extinctions, large numbers of species become extinct each year for tens of thousands to millions of years. Terrestrial biodiversity has experienced five great mass extinctions during the past 500 million years. These mass extinctions have been 20-60 million years apart and there have also been shorter mass extinctions (loss of 15-24% of all species) in between. A period of mass extinction is often regarded as having a loss of 25-70% of all species. The extinction of the dinosaurs is a fine example of mass extinction. Scientists argue over the causes of mass extinction. Some say that rapid climate changes such as the ice age caused the extinction of many species, and some say that other catastrophic events such as large volcanic eruptions and meteorites impacts into the earth causes extinction. Nevertheless, mass extinction which can be the bane of one species, however, can become an opportunity for another. How, after five mass extinctions, could there be such an immense amount of biodiversity today? This fact can be explained by the concept of adaptive radiation. Adaptive radiations are evidence of the earth's capability to regenerate biodiversity. All mass extinctions have been followed by periods of recovery, known as adaptive radiations. After almost every mass extinction, numerous new species have evolved to fill new or vacated ecological niches in the changed environment. The extinction of dinosaurs, for example, was followed by an explosive rise of mammals. Fossil records suggest about 10 million years or more are required for adaptive radiations to rebuild biological diversity after a mass extinction. Go back to: Challenges | Next Section: Endangered Species
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