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Extinction (Dinosaurs)

The following is Box 6-4 in Chapter 6, Evolutionary Record, in my 
college textbook, "Understanding Physical Anthropology and Archeology", 
4th Ed., 1990, Robert Jurmain, Harry Nelson, William A. Turnbaugh, pub- 
lished by West Publishing Company.  Note: An "*" shows italics.
QUOTE - "The theories that have been propounded (to explain the 
extinction of dinosaurs) are legion, and one cannot do better than 
quote Jepsen on this topic: 'Authors, with varying competence, have 
suggested that the dinosaurs disappeared because the climate 
deteriorated (became suddenly or slowly too hot or cold or dry or wet), 
or that the diet did (with too much food or not enough of such 
substances as fern oil; from poisons in water or plants or ingested 
minerals; the bankruptcy of calcium or other necessary elements). Other 
writers have put the blame on disease, parasites, wars, anatomical or 
metabolic disorders (slipped vertebral discs, malfunctions or imbalance 
of hormone or endocrine systems, dwindling brain and consequent 
stupidity, heat sterilization), racial old age, evolutionary drift into 
senescent overspecialization, changes in the pressure or composition of 
the atmosphere, poison gases, volcanic dust, excessive oxygen from 
plants, meteorites, comets, gene pool drainage by little mammalian 
egg-eaters, overkill capacity by predators, fluctuation of 
gravitational constants, development of *psychotic suicidal factors*, 
entropy, cosmic radiation, shift of Earth's rotational poles, floods, 
extraction of the moon from the Pacific Basin, drainage of swamp and 
lake environments, sunspots, God's will, mountain building, raids by 
little green hunters in flying saucers, lack of even standing room in 
Noah's Ark, and palaeoweltschmertz'" (Jepsen, in Halstead, 1968,
pp. 146-147).
*Update*  In 1980, four University of California, Berkeley, scientists 
proposed an extraterrestrial cause for the extinction of many species 
of plants and animals, including dinosaurs, at the end of the 
Cretaceous. They reasoned that meteoritic material, especially iridium, 
which is very rare on earth and could only have come from an extra- 
terrestrial source, was found in deposits of the Cretaceous-Tertiary 
(abbreviated as K-T) boundary in Italy, Denmark, New Zealand, and else- 
     The Berkeley group theorized that an asteroid struck the earth,
forming an enormous crater over 100 miles across. Dust ejected from the 
crater reached the stratosphere and then spread around the earth. This 
phenomenon effectively blocked sunlight from reach the earth's surface 
for about two and a half years, suppressing photosynthesis. Most food 
chains collapsed and mass extinctions, including dinosaurs, followed.
     Further support for this "Berkeley proposal" has come from two
University of Chicago scientists, David Raup and John Sepkoski, Jr. 
They suggest that extinctions occur in periods of 26 million years, 
driven by solar system or galactic forces. Later, other scientists 
identified this driving force to be a small companion star of our sun, 
dubbed "Nemesis" (often referred to as the "Death Star"). Nemesis, it 
was argued, orbits the sun every 26 million years, and when it 
approaches the sun it passes through a cloud (called the Oort cloud) 
of billions of comets. Because of the gravitational force of Nemesis, 
some of the comets are deflected in random ways and some would move 
toward earth. It would have been one of these that struck the earth 
and wreaked the havoc of mass extinctions.
     As is the case when new ideas are proposed, scientists agree and
disagree, and Raup admits there is insufficient evidence to settle the 
matter. Opponents to the Nemesis theory have raised a number of 
(1)  Isn't this a form of Cuvier's catastrophism (see Chapter 2) that 
was rejected more than a century ago? Is Darwinian fitness no longer 
(2)  What defines mass extinction? When does ordinary extinction become 
mass extinction? Does extraterrestrial action cause immediate mass ex- 
tinction? If an extinction occurs over a long period of time, say a 
million years, can an asteroid be considered the cause?
(3)  How valid are the statistics and the statistical methods used to 
determine the 26-million-year periodicity?
(4)  Is the presence of iridium in the K-T boundary as universal on 
earth as the Berkeley group believes?
(5)  How accurate are the dating methods used to date species that have 
gone extinct?
(6)  What evidence is there for the existence of Nemesis, since no one 
has seen it?
(7)  What about terrestrial explanations such as cooling temperatures 
due to continental drift, sea level fluctuations, sea-floor spreading, 
volcanic activity, and geomagnetic reversals, etc.? Have these been 
studied as thoroughly as they could be?
(8)  Why use *extra*terrestrial phenomena to explain events on earth 
when terrestrial evidence is available? As *The New York Times* puts 
it, "Astronomers should leave to astrologers the task of seeking the 
cause of earthly events in the stars."
     The matter of dinosaur extinction is part of the larger problem of
mass extinctions. No one has yet proposed an explanation that is widely 
accepted by paleontologists, biologists, astronomers, and other 
Alvarez, Luis W., Walter Alvarez, Frank Asaro, Helen V. Michel. 
"Extraterrestrial Cause for the Cretaceous-Tertiary Extinction," 
*Science*, 208:1095-1108, June 6, 1980.
Raup, David M. and John N. Sepkoski, Jr., "Periodicity of 
Extinctions in the Geologic Past," *Proceedings of the National 
Academy of Sciences*, February, 1984.
*Note*: There are far too many references to extinctions to list 
here. *Science*, *Nature*, *The New York Times*, *Time*, *Science 
News*, *The New Scientist*, and other newspapers and journals have 
carried articles on the subject in the past few years. See *General 
Science Index*, *Periodical Index*, *The New York Times Index*, etc. 
for additional references. See also *Nemesis* by David Raup for a 
discussion of extinctions, the star Nemesis, and personal details 
about the scientists who have been working on the subject of 
     Whew!  Quite a typing exercise - please see the groups of eight
questions, some multipart.


Terry W. Colvin <colvint@cc.ims.disa.mil> 
U.S. Message Text Formatting Program; Fort Huachuca, Arizona