Do NOT write on this paper. Return this paper at the end of the class period!
Extinction Hypothesis C – Volcanism
SOURCE # 1 : What Killed the Dinosaurs? - an online resource accessed at
http://www.pbs.org/wgbh/evolution/extinction/dinosaurs/low_bandwidth.html
@2001 WGBH Educational Foundation and Clear Blue Sky Productions, Inc. All Rights Reserved
Hypothesis: Volcanism
Did dinosaurs lose their dominance suddenly or gradually? Some scientists think the answer lies locked within the
remnants of long-dormant volcanoes.
Massive beds of ancient lava found around the world depict an Earth 65 to 70 million years ago where volcanic
eruptions were commonplace.
According to the volcanism hypothesis, this global-scale volcanic activity spewed so much gas, ash, and dust into the
atmosphere that it kept sunlight from reaching Earth's surface. Temperature and plant production plummeted, and
dinosaurs and many other organisms that were poorly adapted to the harsh conditions perished.
Evidence for the Volcanism Hypothesis
Lava Flows
Immense lava flows cover nearly 200,000 square miles of the Deccan region of India, reaching
depths of more than 6,500 feet in places. Lava flows like these provide evidence of a rash of
volcanic activity for at least 500,000 years leading up to the extinction of the dinosaurs.
Rare Metal
The metal iridium, which is similar to platinum, is very rare on Earth's surface but is more common
in asteroids and in molten rock deep within the planet. Some scientists think the presence of high
concentrations of iridium at the geological layer associated with the dinosaur extinction could be the
result of extremely large-scale volcanic activity.
Fractured Crystals
These crystals, often called "shocked quartz," show a distinctive pattern of fracturing caused by
high-energy impacts or explosions. Although geologists generally acknowledge that a comet or
asteroid impact would cause these fractures, some scientists conclude that they could also be the
result of volcanic eruptions.
Fossil Record
A gradual decline in the number of dinosaur species would likely mirror an equally gradual cause of
their ultimate extinction. Conversely, a sudden "now you see them, now you don't" end to the
dinosaurs implies a catastrophic cause. Depending on location and interpretation, the fossil record
seems to say different things. A gradual decline in the number of dinosaur species would likely
mirror an equally gradual process like climate change caused by global volcanism.
SOURCE # 2: What Killed the Dinosaurs? - an online resource accessed at
http://www.ucmp.berkeley.edu/diapsids/dinobuzz.html:
DinoBuzz web-site from the University of California Museum of Paleontology © 1994–2006
by the Regents of the University of California.
The "intrinsic gradualists"
Those scientists falling into this category believe that the ultimate cause of the K-T extinction was
intrinsic; meaning of an Earthly nature; and gradual, taking some time to occur (several million years).
Two main hypotheses exist today:
1. Volcanism: We are quite certain that the end of the Cretaceous period that there was increased
volcanic activity. Over a period of several million years, this increased volcanism could have
created enough dust and soot to block out sunlight; producing the climatic change. In India
during the Late Cretaceous, huge volcanic eruptions were spewing forth floods of lava which
can be seen today at the K-T boundary (these ruptures in the Earth's surface are called the
Deccan traps). The chemical composition of the lava rocks in India shows that they originated in
the Earth's mantle, which is also relatively rich in iridium. This richness would explain the iridium
layer.
2.
Plate Tectonics: Major changes in the organization of the continental plates (continental drift) were occurring at the
K-T boundary. The oceans (especially the Interior Seaway in North America) were experiencing a regression; they
were receding from the land. A less mild climate would have been the result, and this would have taken a long time.
Large scale tectonic events did occur in the Mesozoic several times, and no extinction events have been conclusively
associated with them yet.
Note that these two above hypotheses are inextricably tied together; volcanism cannot occur without
the action of plate tectonics, and vice versa. If the extinction was intrinsic and gradual, both processes
probably played a role.
Do NOT write on this paper. Return this paper at the end of the class period!
SOURCE # 3 : Guide to the DinosaursDinosaur
of Colorado?
- an online resource accessed at
Extinction
http://webspinners.com/dlblanc/paleo/dino-colo/index.php
A resource of the Morrison Museum in Colorado Written by Donald L. Blanchard @2004
Volcanic Eruptions - The Deccan Traps:
The basaltic lava eruptions of the Deccan Traps of western India (the Deccan is a region of India, and
'traps' comes from a Dutch word meaning 'staircase'.) was mentioned as a possible source of the iridium
found in the K/T boundary "iridium spike." It has been proposed that the outgassing, combined with
possible explosive episodes, could have been sufficient of itself to have caused the same kind of a
"Nuclear Winter" scenario as proposed for the giant meteor impact.
While this possibility cannot be easily refuted, it seems unlikely, given the nature of the lava flows that
make up the Traps. These flows were caused when the Indian subcontinent passed over the Chagos
Archipelago plume as India drifted north to collide with Asia. The Deccan Traps were produced over a
span of some 500,000 years by basaltic fissure flows, very similar to the eruptions that regularly occur in
Iceland. Basalt has little trapped gas in it, and tends to erupt non-explosively, rather flowing smoothly,
and sometimes nearly continuously, much like the current round of eruptions in Kilauea, Hawaii. Where
plumes lie under continents, they do tend to produce occasional, but very infrequent, explosive events,
leading to the formation of a caldera, which eventually fills in with fissure flow basalt. Yellowstone
National Park lies in just such a caldera, and sometime in the next few thousand or tens of thousands of
years, Yellowstone will be covered over by fissure flow basalts. The basalts of the Snake River Valley
mark the location of past calderas, now obliterated by fissure flow lavas. In fact, the Snake River Basalts
and the Yellowstone Park are a currently active example of exactly the process which formed the Deccan
Traps. This process is really quite common in the geological history of the Earth, and only coincidently
seems to be associated with a mass extinction. Certainly we are not suffering, nor have suffered in the
recent past, from an ecological collapse caused by the Snake River Basalts or the Yellowstone Caldera.
