Dinosaur Extinction Theories
Two
main theories exist in paleontology (the study of dinosaurs) today, each having a different view of what
killed the dinosaurs and other organisms at the K-T boundary. K-T stands for Cretaceous-Tertiary, which marks the time between when dinosaurs existed and when they were extinct. Evidence found in this layer of the Earth's crust helps unlock the mystery of what caused this mass extinction.
There are a few things that scientists can generally agree upon. One of which is that there was a global
climatic change. Climate is the weather in an area over many years. It's believed that the environment changed from a warm, mild one to a cooler,
more varied one (sometimes very hot, sometimes very cold). However, the cause
of this climate change, and the speed at which it occurred differ according to
the various theories.
Another fact that can usually be agreed upon is that
along with the climate change there was also a massive disturbance on the
earth, which threw up soot (fine black particles made of carbon) into the air, causing short-term acid rain, a
release of poisonous gases, and drastic cooling. The long-term consequence of
this disturbance would have been a global greenhouse effect (warming and
reduced sunlight). 
The last piece of common ground between scientists is that
in several places around the globe, at or near the K-T boundary, there is a
thin layer of clay with an unusually high content of iridium (a rare metal
similar to platinum). The high amount of iridium may be evidence for the dust
cloud.
Source: http://www.ucmp.berkeley.edu/diapsids/extinctheory.html
Select a Theory
*Although you are welcome to research other theories, these are the two most widely accepted theories in paleontology.
Asteroid/Meteor
Volcanism
Websites to check out:
*This website has some excellent background information under Extinction: Why did the dinosaurs go extinct? “What is Extinction”, “The Alvarez Asteroid Theory,” and “Other K-T Extinction Theories” are good sources for you to get research information from.
*This is an interactive website! You can click on the different theories and look at the evidence supporting each one. Make sure to check out all of your options.
*Scroll down the page to check out information on the various extinction theories.
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