Mass Extinction Essay -- K-T Extinction

ABSTRACT Several mass extinctions have occurred during the Earth’s history. The Cretaceous – Tertiary Boundary (K-T) Extinction caused the loss of at least 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 it’s occurrence is abundant. INTRODUCTION The 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. Controversy 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 slow and gradual Earth generated event, caused by intense volcanic activity 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. Th is creates the stepladder effect of evolution seen in the fossil record . THE K-T EXTINCTION The Cretaceous period occurred between 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 (â€Å"The End-Cretaceous (K-T) Extinction†, accessed 2000). Among the species that perished were the dinosaurs, pterosaurs, belemnoids, many species of plants, except ferns and seed-producing plants, ammonoids, 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 (â€Å"The End-cretaceous (K-T) Extinction†, accessed 2000... ...pdated 1995, accessed 3 Sept. 2000), Dino Buzz – What killed The Dinosaurs ? – Current Arguments, http://www.ucmp.berkeley.edu/diapsids/extinctheory.html Lowood, 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.html Smith, P.L. 1997a (updated 1997, accessed 3 Sept. 2000), Biological Evidence, http://www.science.ubc.ca/~geol313/lecture/kt/biol/biol.htm Smith, P.L. 1997b (updated 1997, accessed 3 Sept. 2000), The Marine Realm, http://www.science.ubc.ca/~geol313/lecture/kt/biol/marine/marine.htm Smith, P.L. 1997c (updated 1997, accessed 3 Sept. 2000), The Terrestrial Realm, http://www.science.ubc.ca/~geol313/lecture/kt/biol/terres/terres.htm Smith, P.L. 1997d (updated 1997, accessed 3 Sept. 2000), Geological Evidence, http://www.science.ubc.ca/~geol313/lecture/kt/geol/geol.htm â€Å"Speculated Causes of the End-Cretaceous Extinction† (accessed 3 Sept. 2000), http://www.wf.carleton.ca/Museum/cretcause.htm â€Å"The End-Cretaceous (K-T) Extinction† (accessed 3 Sept. 2000), http://www.wf.carleton.ca/Museum/cretmass.htm