Hypothesized Causes of Mass Extinctions

Paper Summary:

This paper defines what is meant by mass extinction and discusses a few that have occurred on our planet and some of the theories that have attempted to explain them. The writer explains that while some believe in meteorites or comet showers, and others in volcanism, variations in sea level, global climate changes and changes in ocean levels of oxygen, still a third group of scientists believe it was likely a combination of two or more of these events. The paper concludes that it is still unclear exactly what caused mass extinctions, and because of the elapsed time it is doubtful that we will ever know for sure.

From the Paper:

"Most of us are, of course most familiar with the extinction of the dinosaurs. Practically every child is fascinated by these huge beasts that roamed our planet at one time and now do not exist at all. In 1979 Berkeley scientists discovered a piece of pink and white limestone which contained evidence of what the scientists called "the great dying." (Rogers 1). The rock was found near Gubbio, Italy, and was at one time under the sea. To make an involved story short, the Cretaceous limestone has many fossils of tiny crustaceans while these little crustacean fossils are entirely absent from the clay layer, reappearing again in the Tertiary limestone. The scientist measured the presence of iridium, and found a substantial increase in the clay--twenty five times more than normal."

Sample of Sources Used:

• BBC News. Asteroid Destroyed Life 250 Million Years Ago. 23 February 2001. Accessed 9 September 2006. <http://www.news.bbc.co.uk/2/low/science/nature/1184556.stm>
• Daley, Beth. In Crater, a Clue to Ancient Extinction. 14 May 2004. Accessed 10 September 2006. <http://www.boston.com/news/nation/articles/2004>
• Extinction Events. What was the Largest Mass Extinction Event? 2006. Accessed 11 September 2006. <http://www.lakepowell.net/sciencecenter/extinction_events.htm >
• Extinction Theories. The Great Mystery--What Killed the Dinosaurs? 2006. Accessed 12 September 2006. <http://www.ucmp.berkeley.edu/diapsids/extinctheory.html >
• Infoplease. Mass Extinction. 2006. Accessed 11 September 2006. <http://www.infoplease.com/ce6/sci/A0832139.html>

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