Earth has been wrought by mass extinctions, the causes of which have been debated for years. For example, renowned biologist and researcher, E.O. Wilson, notes that the earth appears to have cooled significantly during all of the first four mass extinctions, the first three cooling events possibly being caused by continental drift. This, coupled with the fact that no iridium was found in deposits dating from those time periods, led him to conclude that the first four mass extinctions were not attributed to asteroids or volcanoes, but more likely, to climate change (Wilson, 1992).
However, Niles Eldredge, paleontologist and author of Life in the Balance: Humanity and the Biodiversity Crisis, believes the causes may not be quite so cut and dried. According to Eldredge, the Ordovician extinction, which occurred approximately 440 million years ago, was probably caused by climate change, but the Devonian extinction of 370 million years ago, may or may not have been caused by climate change. He believes the Permian extinction of 245 million years ago could have been caused by a bolide impact similar to that at the end of the Cretaceous period, and that the cause of the Triassic extinction 210 million years ago is still largely unknown (Eldredge, 2001). This supports what Wilson reports in his book, The Diversity of Life, when he speaks of the opposing arguments regarding the cause of the Cretaceous extinction 65 million years ago. Basically, there are numerous theories to consider, many having much scientific evidence to back them up. For the first four extinctions, however, climate change does seem to be the prevailing theory (Wilson, 1992).
With this history in mind, we may ask ourselves what will cause the next mass extinction on earth. The answer, unfortunately, seems to point directly at humanity itself. Current life on earth is threatened, because due to human-accelerated global warming, we are headed towards an Anthropocene extinction event (4ecotips, 2006), meaning one caused by man. Similar to other extinction events, such as at the end of the Cretaceous period, when scientists believe an exploding asteroid produced meteorites that fell to the Earth (Mader, 2007), this extinction will likely be just as severe, yet may occur over a longer period of time. As the earth warms, the polar ice caps will melt and oceans will rise, severely flooding cities all along the eastern coast of the United States, perhaps even covering a large portion of Florida (Lovgren, 2004). It is predicted that the world’s oceans will become so acidic that coral reefs will disintegrate, Mediterranean forests will burn year round, and many parts of the world will be so hot they can no longer support human life. As a result, all those who have the means will flock to the half of the world that is still habitable, placing even stronger pressures on already-stressed ecosystems (4ecotips, 2006). Species will become extinct by the thousands, having not enough time to adapt to their changing world. As the cycle continues, food will become scarce to the point that, those humans that have not already died from their now toxic surroundings, will follow this course of extinction as well.
If this all occurs, we will likely experience a mass extinction, followed by a period of accelerated evolution, resulting in a planet unrecognizable when compared to its current existence.
4ecotips. (2006). Global warming threatens no future for life on earth. Retrieved March 27, 2009, from http://www.4ecotips.com/eco/article_show.php?aid=782&id=240
Eldredge, N. (2001). The sixth extinction. Retrieved April 5, 2009, from http://www.actionbioscience.org/newfrontiers/eldredge2.html#primer
Lovgren, S. (2004). Warming to cause catastrophic rise in sea level? Retrieved, March 26, 2009, from http://news.nationalgeographic.com/news/2004/04/0420_040420_earthday.html
Mader, S.S. (2007). Biology (9th ed.). New York, NY: McGraw Hill.
Wilson, E.O. (1992). The diversity of life. New York, NY: W. W. Norton & Company, Inc.