Biological extinction occurs whenever a species of animal or plant life is permanently lost. Because of a variety of factors, the earth is currently losing "perhaps one species per day" (5:338). One of the strongest factors in causing this loss is human activity. For example, hunting, pollution, and the clearing of the rain forests can all be blamed for the destruction of many species. The issue of biological extinction raises questions regarding the threat of mass extinction. Mass extinction occurs when a large number of different species die out during the same period of time. Human beings are dependent upon the natural ecosystem for their survival. Mass extinction would have an adverse effect on the balance of nature as it exists in the world today. As such, the threat of mass extinction has important implications for the future fate of humankind.
Fossil records indicate that five mass extinctions occurred during prehistoric times. The latest such extinction occurred approximately 65 million years ago, at the end of the Cretaceous era. At that time, the dinosaurs were wiped off the face of the earth. In addition, "about 15% of known marine animal families became extinct" (1:98). Several theories have been advanced to account for the prehistoric extinctions. One such theory proposes that the dinosaurs were poisoned by the flowering plants which first started flourishing during that time (5:193). Another theory, known as the Impact Theory, was first proposed by Walter Alvarez in the late 1970's. Alvarez discovered large amounts of iridium in various parts of the earth. Iridium is not indigenous to the earth and is usually found only on the meteorites and other heavenly bodies which have crashed on the planet. Because of this, Alvarez theorized that a huge asteroid or comet hit the earth during the late Cretaceous period and created a cloud of dust which blocked the sun. Without sunlight, most of the plants becam...