There are many excellent websites that discuss the K-T extinction:
Earth and Life History (Earth Sciences)
4. Evidence from rocks allows us to understand the evolution of life on Earth. As a basis for understanding this concept:
a. Students know Earth processes today are similar to those that occurred in the past and slow geologic processes have large cumulative effects over long periods of time.
b. Students know the history of life on Earth has been disrupted by major catastrophic events, such as major volcanic eruptions or the impacts of asteroids.
e. Students know fossils provide evidence of how life and environmental conditions have changed.
g. Students know how to explain significant developments and extinctions of plant and animal life on the geologic time scale.