Mass Extinction Essay -- K-T Extinction

ABSTRACTSeveral mass extinctions have occurred during the Earths history. The Cretaceous third Boundary (K-T) defunctness caused the loss of at to the lowest degree three-quarters of all species known at that time including the dinosaurs. The cause of this mass extinction is a controversial subject among scientists but the fossil evidence of its accompaniment is abundant.INTRODUCTIONThe K-T Extinction occurred 65 million years ago. Many species perished in that extinction. Today evidence for this extinction can be seen in the fossil record. Biological, botanical and geological evidence at the Cretaceous Tertiary Boundary show that some enormous event occurred that caused mass extinction of life on the Earth. dissension about the cause of the K-T extinction exists with two main theories currently being in favour. One theory is called Intrinsic Gradualism and believes the cause of the K-T Extinction was a unwind and gradual Earth generated event, caused by intense volcanic acti vity and the effect of plate tectonics. The second theory is known as Extrinsic Catastrophism and proposes that the K-T Extinction was caused by a sudden and violent catastrophic event such as the Earth being struck by a meteor or asteroid. The K-T Extinction supports the concept of Punctuated Equilibrium in evolution because surviving species evolved and others were exterminated. This creates the stepladder effect of evolution seen in the fossil record .THE K-T EXTINCTIONThe Cretaceous period occurred betwixt 144 and 65 million years ago. The K-T Extinction is an event that happened at the end of this period 65 million years ago. By the beginning of the Tertiary period eighty-five percent of all species disappeared, making it the second largest mass extinction event in geological history (The End-Cretaceous (K-T) Extinction, accessed 2000).Among the species that perished were the dinosaurs, pterosaurs, belemnoids, many species of plants, pull up ferns and seed-producing plants, a mmonoids, marine reptiles and rudist bivalves. Severely affected organisms included planktic foraminifera, calcareous nannnoplankton, diatoms, dinoflagellates, brachiopods, mollusca, echinoids and fish. Mammals, birds, turtles, crocodiles, lizards, snakes and amphibians fared much better and were mostly unaffected by the End-Cretaceous mass extinction (The End-cretaceous (K-T) Extinction, accessed 2000... ...pdated 1995, accessed 3 Sept. 2000), Dino hum What killed The Dinosaurs ? Current Arguments,http//www.ucmp.berkeley.edu/diapsids/extinctheory.htmlLowood, H. 1998 (updated 7 Sept 1999, accessed 30 June 2000), Stanford Presidential Lectures and Symposia in the Humanities and Arts, Stephen Jay Gould,http //prelectur.stanford.edu/lecturers/gould/index.htmlSmith, P.L. 1997a (updated 1997, accessed 3 Sept. 2000), Biological Evidence,http//www.science.ubc.ca/geol313/lecture/kt/biol/biol.htmSmith, P.L. 1997b (updated 1997, accessed 3 Sept. 2000), The Marine Realm,http//www.science.u bc.ca/geol313/lecture/kt/biol/marine/marine.htmSmith, P.L. 1997c (updated 1997, accessed 3 Sept. 2000), The Terrestrial Realm,http//www.science.ubc.ca/geol313/lecture/kt/biol/terres/terres.htmSmith, P.L. 1997d (updated 1997, accessed 3 Sept. 2000), Geological Evidence,http//www.science.ubc.ca/geol313/lecture/kt/geol/geol.htmSpeculated Causes of the End-Cretaceous Extinction (accessed 3 Sept. 2000),http//www.wf.carleton.ca/Museum/cretcause.htmThe End-Cretaceous (K-T) Extinction (accessed 3 Sept. 2000),http//www.wf.carleton.ca/Museum/cretmass.htm