Extinction is the end of an organism or group of taxa. Extinctions occur when a species becomes unfit for survival in its natural habitat usually to be replaced by another, better-suited species. An organism becomes ill-suited for survival because its environment is changed or because its relationship to other organisms is altered as stated from Credo Reference. The moment of extinction is generally considered to be the death of the last individual of that particular species. Mass extinctions, however, are rare events that only happen every few million years. Only recently have these events been recorded and scientist have become alarmed at these recent extinctions. Most extinctions aren’t even documented and some predict that most of present species will be gone by the year 2100. Many scientist seek to find out what causes mass extinctions, the consequences of these events, and if another extinction in the near future. In the past 500 million years, five mass extinctions have occurred according to fossil record. In each event 50% or more of our planet’s species became extinct (Campell). They occurred at the end of the Ordovican, late Devonian, the end of Permian, the end of Triassic, and the end of Cretaceous period (Thomas). Of all the mass extinctions, the Permian and Cretaceous periods received the most action. The Permian mass extinction occurred about 251 million years ago and took about 96% of marine animals. It also took a huge toll on terrestrial animals. About 65 million years ago in the Cretaceous period, the earth had another mass extinction (Campell). During this day and age, dinosaurs reined the land and pterosaur ruled the sky. The causes of extinctions can be broken down into two different categories which are, terrestrial and extraterrestrial. Firstly, in terrestrial causes, moving continents can be a major factor in extinctions. When all land masses combine, the global diversity will be lower than the different continents. With this, different...
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