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
- 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,
- 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
- 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
- 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.
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Last modified by
pib on July 6, 2003.