Extinction is defined as the end of existence of a group of organisms, caused by their inability to adapt to changing environmental conditions. Throughout the existence of our planet there have been large amounts of species extinctions. For instance, the dodo, a species of flightless pigeon formerly living on the island of Mauritius, became extinct in 1665. About 10,000 to 12,000 years ago, the most of the woolly mammoths and the last of the mastodons, both members of the elephant family, died. Also about 245 million years ago at the end of the Paleozoic Era, an entire class of primitive marine animals called trilobites disappeared forever.
Over the years we have learned that extinction is a natural and ongoing phenomenon. In effect, of the hundreds of millions of species that have lived on Earth over the past 3.8 billion years, more than 99 percent are already extinct. This extremely high rate of extinction can be linked to several factors. Some of this happens as the natural result of competition between species, and is known as natural selection. According to natural selection, living things must compete for food and space. Those species incapable of adapting are faced with imminent extinction. This constant rate of extinction is sometimes called background extinction. Normal rates of background extinction are usually about five families of organisms lost per million years.
Due to several fossil finding, we know that not all extinctions are constant and gradual, some are unpredictable and extreme. The cause of these large-scale extinctions is always dramatic environmental change that produces conditions too severe for organisms to endure. Environmental changes of this caliber result from extreme climatic change, such as the global cooling observed during the ice ages, or from catastrophic events, such as meteorite impacts or widespread volcanic activity.
Extinction is a timeless trend, in fact, most scientists agree that life…

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