As many as 500 million kinds of plant, animal and microorganism have made this planet home since life began over 3.5 billion year ago.
Today, there are only 5 million to 10 million species alive we do not know exactly how many, because there are many biologically uncharted areas such as the tropical rain forests where some estimate that such as the tropical rain forests, where some estimate that over 90% of the living organisms remain unclassified. Thus, since life began, about 490 million species have become extinct.
As study of the history of life from an evolutionary prespective tercher us that biological extinction is a fact of life. As species evolve, the old give way to the new. Many of the so called extinct species are represented today by their descendants. Thus, many species did not off as such but were simply altered during evolution.
Other species vanished completely as a result of drastic climatic changes or increasing environmental resistance created by excess predation or disease.
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The dinosaurs, for example, perished rather abruptly all over the world 65 million years ago, possibly as a result of global cooling.
Much more recently, at the end of the pleistocene epoch 10,000 years ago, many large mammals such as the sabertooed tiger and giant tree sloth vanished from North America. Their extinction resulted either from climatic changes at the end of the Ice Age of possibly from Siberia.
As these people moved south and east, they hunted the large mammals such as they wooly mammoth wooly rhinoceros, giant deer, ground sloth, mastodons, giant beavers, sabertoothed tigers, bibson, and elk. They undoubtedly also competed for the same food resources.
From the end of Pleistocene until now, the earth’s climate has been fairly constant and relatively few plants and animals have become extinct in the 1800s, 84 animals species and subspecies are known to have vanished.
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By 1984 the number had risen to 184, and if trends continue, many scientists believe, 170 more species will disappear by 2000, bringing to total to more than 350 if conditions turn considerably wore. More than 700 additional species might be destroyed before the end of the century.
One vertebrate species is becoming extinct every nine months, compared with a natural rate of one species every thousand years. When plants, insects, and microbes are added, the rate may be as high as one species per day. Ecologists argue that plant extinctions will have much more profound impacts on the ecosystem the extinction of animals, because plants from the base of the food web.
Some authors assert that if the world’s population continues to grow and nations continue to destroy wildlife habitat by expanding agriculture and other activities at the current pace, the extinction rate could reach 20,000 species a year. At the rate 400,000 species of plants and animal could be wiped out in 20 years.
World wildlife expert Norman Myers argues that we could lose 1 million species by 2000. Although such high rates of extinction are probably exaggerated extinction will undoubtedly increase unless we make conscious efforts to curb population growth and properly manage our renewable and nonrenewable resources.