Catastrophism and Mass Extinctions

From the middle of the nineteenth century until about 1980, most geologists and other earth scientists opposed the idea that impact events played any significant part in the history of life on earth.

In 1980 Walter and Luis Alvarez and their colleagues Frank Asaro and Helen Michel published an historic paper suggesting that an asteroid about 10 kilometers (6 miles) in diameter struck the earth sixty-five million years ago at the end of the Cretaceous. The resulting impact should have left a crater at least 160 kilometers (100 miles) in diameter. If the impact site were in the ocean, huge tsunami ("tidal waves") would rise several kilometers in height, sweeping hundreds of kilometers across the continents, sweeping away everything in their path. As hot material ejected from the impact rained back down, huge fires would start up all over the world. Dust thrown up by the impact would have spread out covering the entire world in darkness. Temperatures would have dropped precipitously. Plants would have failed to receive enough sunlight to allow photosynthesis to continue. After the plants died, plant-eating animals dependent on them would die, as would meat-eating animals once their plant-eating prey were gone. Conditions in the oceans would not be much better as massive acid rain buildup poisoned the water and destroyed shell-bearing creatures, disrupting the entire food chain. About 70% of all species died out at the end of the Cretaceous. This included the dinosaurs which had dominated the landscape for over 160 million years.

Since 1980, the theory that the impact of a large asteroid or comet brought about the demise of the dinosaurs and many other forms of life at the end of the Cretaceous (the "K-T boundary") has gained in popularity. Some scientists remain unconvinced by the evidence, however. The following web pages discuss this mass extinction event as well as others before and since.

• Asteroids of Death by E.S. Matalka discusses the asteroid impact hypothesis for the extinction of the dinosaurs. Matalka is critical of this idea. He suggests David Archibald's marine regression hypothesis is more likely.
• Carriers of Extinction by Carl Zimmer suggests that the megafaunal extinctions at the end of the last ice age were caused by pathogens carried by migrating humans.
• Chicxulub Impact Crater Provides Clues to Earth's History by Virgil L. Sharpton dicusses the most likely site for the main impact at the end of the Cretaceous, Chicxulub in the Yucatan, Mexico.
• Chicxulub Seismic Experiment discusses an ongoing project by the Crustal Geophysics group at Imperial College, London, U.K. to study the Chicxulub impact structure. In the summer of 1996 the group acquired a series of wide-angle and normal-incidence reflection seismic profiles onshore and offshore across the structure.
• Cracking The Mystery by Anthony Spaeth discusses the suggestion by Sankar Chatterjee and Dhiraj Kumar Rudra that a 600 km crater, mostly submerged in the Arabian Sea off Bombay, India, is the site of the "dinosaur killer" impact at the end of the Cretaceous. Chaterjee and Rudra suggest that this "Shiva crater" and that one at Chixculub were caused by fragments of the same large object striking about 12 hours apart as the Earth rotated.
• Crashing Comets and Dead Dinosaurs offers an overview of the impact theory for the dinosaur extinction at the end of the Cretaceous. There's also an interesting description by Dennis Schatz of how to make your own comet for classroom demonstrations.
• Crater of Death provides the transcript of a BBC television program about the Chicxulub crater and the end-Cretaceous extinction event.
• Dinosaur Extinction: One More Hypothesis offers the text of the 1956 paper by M. W. De Laubenfels from the Journal of Paleontology suggesting a large impact might have caused the end-Cretaceous dinosaur extinction.
• Dinosaur Extinction Page by A. Buckley discusses the asteroid impact and volcano theories for the demise of the dinosaurs.
• Dinosaur Volcano Greenhouse Extinction by Dewey McLean discusses the volcano versus asteroid extinction theories. McLean is the originator of the volcano theory, which couples the K-T extinctions to a major perturbation of earth's carbon cycle caused by the Deccan Traps mantle plume vulcanism.
• Dinosaurs, Comets, and Asteroids --Resources from NASA offers an excellent list of web sites, books, article, teacher's resources about impact-induced extinctions.
• Dinosaurs -- Fact Sheet discusses why they went extinct.
• Disaster from space discusses evidence in favor of a large impact event causing the extinction at the end of the Cretaceous.
• Do or Die: Extinction from the St. Louis Science Center summarizes several ideas about why the dinosaurs became extinct at the end of the Cretaceous.
• Dusk Of The Dinosaurs by Michael J. Benton reviews two books about the dinosaur extinction controversy: T.Rex and the Crater of Doom by Walter Alvarez and The Great Dinosaur Extinction Controversy by Charles Officer and Jake Page.
• End of a Legacy: How did the dinosaurs meet their demise? by Andrew Maas is an eigth grade science project surveying some of the possible causes for the extinction of the dinosaurs.
• Extinction pages lists Web pages which discuss extinctions.
• Extinctions due to impacts, past and future offers the abstract and audio (RealAudio format) of a presentation by Owen Toon.
• Extinctions: Cycles of Life and Death Through Time from the Hooper Virtual Paleontological Museum discusses the asteroid impact and volcano hypotheses for the end-Cretaceous extinction. Includes sections on mass extinctions in Earth history, minor extinctions, patterns of extinction, extinction in the early Holocene, and more.
• Georges Cuvier (1769-1832) was one of the founders of vertebrate paleotology. Cuvier established extinction as a fact. He ascribed extinctions to periodic "revolutions" or catastrophes, events which Cuvier cosidered to have natural causes.
• Impact Catastrophe that ended the Mesozoic describes a Hypercard stack for the Macintosh which discusses the impact catastrophe at the end of the Cretaceous.
• K-T Event discusses the impact event at the end of the Cretaceous.
• Mass Extinctions deals with the dinosaur extinction as well as mass extinctions in general.
• Possible Collisions on Earth due to Asteroids and Comets by Karen Krupinsky and Tammy Seergae offers a student activity to research and evaluate different theories for the extinction of the dinosaurs, including the impact hypothesis.
• Scientists find evidence of dinosaur-killing asteroid - Feb. 16, 1997 offers the text of an AP wire story detailing new evidence supporting the impact hypothesis for the extinction of the dinosaurs. Core samples in the Caribbean indicate a "dead zone" lasting about 5,000 years after the impact.
• Sky is Falling! or What Did in Dino? discusses the end-Cretaceous impact extinction hypothesis.
• T-Rex and the Death Star from the H. V. McKay Planetarium in Melbourne, Australia discusses the impact theory for the extinction of the dinosaurs.
• What killed the dinosaurs? surveys a number of different hypotheses advanced to explain the extinction of the dinosaurs.
• Brian Goff's What killed the dinosaurs? is critical of the impact theory for the demise of the dinosaurs.
• What Really Killed the Dinosaurs? from New Scientist, August 16, 1997 discusses the asteroid impact, volcano, giant molecular cloud, and giant disintegrating comet hypotheses.
• When the sky fell on our heads: Identification and interpretation of impact products in the sedimentary record by Philippe Claeys assesses the geological evidence for a killer strike in terms of impact products at the end of the Cretaceous.
• Works in Progress: Extinction reports on recent research into a simple model of extinction proposed by Mark Newman and Gunther Eble. They suggest all extinction is caused by environmental stresses, such as the impact that killed the dinosaurs.

The growing popularity of the impact theory as an explanation for the extinction at the Cretaceous-Tertiary boundary opened the door to a reexamination of the role played by impact processes in shaping Earth history. The following web pages show how such neo-catastrophist thought now influences the teaching of geology.

• Earth, Wind, and Fire -- A Catastrophist View of Geology presents the syllabus of a course taught by Philip Allen and Alex Densmore at the University of Dublin, Trinity College. Allen and Densmore state that "Earth's history can be thought of as a slow, gradual story punctuated by a series of catastrophic events that have irrevocably affected the earth and its inhabitants. Our aim in this course is to introduce you to the way the earth formed and how it works, focusing on big events like meteorite impacts and mass extinctions, as well as more commonplace disasters like earthquakes, volcanic eruptions, and floods. By learning about these events, you'll learn a bit about the way things were, the way things are, and the way things will be - all of which are of interest to the earth sciences."
• The Fall and Rise of Catastrophism is based upon a lecture by Trevor Palmer given at Nottingham Trent University on April 25, 1996. Palmer discusses the history of orthodox catastrophist thinking, from its low point in the middle of the last century, to the current neocatastrophist revival.
• Geology 204 Natural Disasters is the syllabus for a course by Steven A. Nelson at Tulane University which discusses cosmic impacts as well as earthquakes, volcanos, landslides, subsidence, flooding, exceptional weather, coastal erosions, and other natural disaster.

Back to catastrophism.
Back to my interests.
Back to my home page.

Last modified by pib on July 6, 2003.