Extinctions on Earth

The Extinctions on Earth


Considering all the great cataclysms in the Earth throughout its long history, it is remarkable how life has managed to survive to the present. Over ninety-nine percent of all species that have inhabited the planet from the beginning have become extinct, so that those living today represent only a tiny fraction of the total. Billions of plants and animals have existed in the geologic past. Most lived during the last six hundred million years. A period of phenomenal evolution of species as well as tragic mass extinctions. The common denominator in all mass extinctions is that biological systems were in severe stress due to rapid and extreme changes in the environment. The ultimate environmental hazard is mass destruction by the impact of a meteorite, asteroid, or comet on the Earth. Over one hundred large meteorite craters have been located throughout the world, some which might be associated with mass extinctions of species. The impact of aste...