Cretaceous-Tertiary Boundary: A Great Enigma

This page was written by Jen Aschoff as part of the DLESE Community Services Project: Integrating Research in Education.

The Z-coal at the top of the Hell Creek Formation marking K-T boundary in Montana. Details

What is the nature of the K-T boundary and how is it related to the extinction of the Dinosaurs?

There are numerous suitable thought pathways by which to explore such a question. Below, we have suggested one such pathway.

Read more about this pathway to discovery here...

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In this pathway, we begin with the most basic questions, provide resources to help answer these questions, and progress to more complex questions. The end result is not an answer, but a better understanding of contemporary arguments and supporting data concerned with the "big question". Students and instructors are encouraged to discuss favored hypotheses and provide data and reasoning to support a particular "favored" hypothesis.

Show list of questions comprising our pathway

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1. What is mass extinction?
2. What criteria must be present to infer a mass extinction? And, which of these criteria exist for the Cretaceous-Tertiary extinction?
3. Why do certain groups of organisms survive while others diminish?
4. What groups of organisms were affected by the K-T "event"? What does this tell us about possible causes of the extinction?
5. What ideas have been proposed to explain the Cretaceous-Tertiary mass extinction?
6. What geologic problems or limitations exist that make the K-T boundary and extinction question inherently difficult questions to answer?

Pathway to Discovery:

1. What is mass extinction?

Helpful Resources:

• Extinction (more info)
• Extinctions: Cycles Of Life and Death Through Time ( This site may be offline. )

2. What criteria must be present to infer a mass extinction? And, which of these criteria exist for the Cretaceous-Tertiary extinction?

Helpful Resources:

• Extinctions: Cycles Of Life and Death Through Time ( This site may be offline. )

3. Why do certain groups of organisms survive while others diminish?

Helpful Resources:

• Survival of the Fittest? (more info)

4. What groups of organisms were affected by the K-T "event"? What does this tell us about possible causes of the extinction?

Helpful Resources:

• What Killed The Dinosaurs?: The Great Mystery ( This site may be offline. )
• Extinctions: Cycles Of Life and Death Through Time ( This site may be offline. )
• Extinction (more info)
• What Killed The Dinosaurs?: The Great Mystery ( This site may be offline. )

5. What ideas have been proposed to explain the Cretaceous-Tertiary mass extinction?

Helpful Resources:

• A Tale of Two Rocks (more info)

6. What geologic problems or limitations exist that make the K-T boundary and extinction question inherently difficult questions to answer?

• What Killed The Dinosaurs?: The Great Mystery ( This site may be offline. )

Suggested Post-exercise Group Discussion Questions:

• Briefly summarize the observations that have been made concerning the K-T boundary and the extinction of dinosaurs.
• Which extinction hypothesis best describes the observations that have been made about the K-T boundary?
• Are there any problems with the science that has been done on this topic?
• What are some possible avenues for future research on this question? Give an example of a project you could do to further our understanding of the K-T boundary.