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?

• Extinction (more info)
A number of extinction concepts are discussed and loosely defined here, followed by a survey of some important extinction and "extinction-like" events, primarily from the Phanerozoic.


• Extinctions: Cycles Of Life and Death Through Time ( This site may be offline. )
Definitions of extinction and a thorough discussion of extinction processes with examples of minor and major extinction events are presented here.

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

• Extinctions: Cycles Of Life and Death Through Time ( This site may be offline. )
Definitions of extinction and a thorough discussion of extinction processes with examples of minor and major extinction events are presented here.

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

• Survival of the Fittest? (more info)
This classroom exercise explores characteristics of a physically "hardy" group of animals, the crocodiles. The purpose of this exercise is to examine data about modern crocodiles and postulate why such creatures have endured much of the geologic past.

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

• What Killed The Dinosaurs?: The Great Mystery ( This site may be offline. )
This site presents some background information about the K-T boundary and supplies information about the kinds of organisms most affected.


• 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?

• 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. )
Some problems with the past and current interpretation of the K-T boundary are outlined here.

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.