Extinctions

Earth is now entering its sixth period of mass extinction, defined as a major decrease in the number of species in a relatively short period of time. Extinctions are a normal part of the evolution of ecosystems. New species evolve, other species die out, and over millennia the diversity of life on the planet has increased.

The previous five mass extinction events are believed to have been caused by prehistoric meteor impacts and/or significant climatic changes (themselves caused by a variety of factors). The fifth event occurred 65 million years ago and wiped out an estimated 50% of Earth's species, including the dinosaurs. In the current time, a similar percentage of Earth's species are again threatened with extinction but this time as a result of the ...