A Mini-Lesson

"THEORY" CHOICES: WHAT HAPPENED TO THE DINOSAURS?

author unknown

EVOLUTION

 SYNOPSIS

 CONCEPTS

NOTICE: The word "theory" is used here in its less restricted sense, referring to a relatively untested yet plausible explanation for a particular event or process. The more accurate term would be "hypothesis". However, in this lesson, for convenience, we will retain the use of "theory", generally in quotation marks to reflect that understanding. It should be made clear to students that neither word should ever be used to represent a casual "guess" or "hunch", as implied in the phrase "It's only a theory".

CONCEPTS

1. Some evolutionary change is rapid and discontinuous.

2. Extinction plays in role in macroevolution.

3. Scientists use specific criteria in deciding which "theory" is better.

STUDENT OBJECTIVES

Students will...

1. be able to list the evidence for a given "theory".

2. be able to compare "theories" on the basis of this evidence.

3. suggest other criteria which could be used to choose best "theory".

4. state how this investigation relates to the fluid nature of science.

 MATERIALS

 STUDENT HANDOUTS

(see end of lesson for the formatted handouts).

 Copies of two articles from Scientific American, Oct.1990. There should be enough so that each student has a copy to take home for homework. Half of each class will do the first article, half will do the second article. (See details and additional articles below, under "SOURCES").

Questions for homework (see end of this lesson)

Questions for in-class group discussion (see end of this lesson)

 TEACHING STRATEGY

TIME:

day 1 - a few minutes to explain the assignment and pass out articles and questions.

day 2 - one full period for group discussion and follow-up class discussion.

TEACHING STRATEGIES:

DAY 1:

THEORY - HYPOTHESIS - GUESS?
Before doing this lesson, be sure that your students are aware of the proper distinction between theory, hypothesis, and a hunch or guess. If this was studied earlier, use this opportunity for review by asking what the two different possible explanations presented for dinosaur extinction would be properly called: theories, hypotheses, or something else [hypotheses]. If not studied earlier, this would be a good time to discuss the proper and inappropriate usages of these terms. They are defined nicely on site by Martin Nickels in his paper on THE NATURE OF MODERN SCIENCE & SCIENTIFIC KNOWLEDGE: Scroll down to part IV of the paper, where these terms are defined.
It should be emphasized that the word "theory" as used in science should NEVER be used for any non-scientific explanation, e.g. a religious belief, or in reference to a casual hunch or guess, as in "it's only a theory" (even though this is, unfortunately, the common colloquial meaning). Also, because a hypothesis may, after some indefinite degree of confirmation, rise to the level of "theory" (or part of a theory), references to a hypothesis as a "theory" should be presented with qualifying quotation marks.

a. Divide students into groups of 4

b. Give two students in each group the article on asteroid extinction ("An Extraterrestrial Impact", by Walter Alvarez and Frank Asaro, Scientific American, Oct.1990, pp.78-84).

c. Give the other two students the article on volcanic extinction ("A Volcanic Eruption", by Vincent Courtillot, Scientific American, Oct.1990, pp.85-92).

d. Give each student a copy of the homework questions (end of lesson) to answer for use next day.

DAY 2:

a. Ask the students to share their answers in their groups.

b. Students should then discuss and answer the group questions.**

c. Class discussion can then follow.

d. You may want to bring in even more "theories" on extinction of dinosaurs, provided in the supplementary articles.

EVALUATION:

1. Answers to individual and group questions can be checked, for accuracy of content, and/or evidence of mental involvement.

2. Given another set of alternative explanations, with evidence, students must demonstrate how they should go about establishing which works best.

EXTENSIONS AND VARIATIONS

It's important that students should be discouraged from using the subjective "going with the explanation that sounds best" approach. They should realize that there are criteria for selecting the better choices.
Provide your students with a copy of the "Fair Tests: Basic Model for Critical Thinking in Science", and ask them to apply those criteria to the above study.

SOURCES:

For an excellent discussion of three different hypotheses on the likely cause of this extinction, get Dinosaurs: The Science Behind the Stories, ed. by Judith Scotchmoor et al, published by the American Geological Institute (2002), and available online from http://www.agiweb.org/pubs/pubindex.html. Note especially chapter 12: Dinosaur Extinction: Changing Views (pages 99-106), where the three hypotheses are presented and discussed. A very recent episode in this controversy was revealed in a Nature news article (10 April, 2003) in which new core samples from the reputed crater suggest an alternative explanation. Click here for a PDF copy of the brief article, along with a few review questions.

Check your local public library or nearby college/university library:

For the two articles used in this lesson:
"Debate: What Caused the Mass Extinction?" by Alvarez, Asaro, and Courtillot, Scientific American, Oct.1990, pp.76-92.

Most recent article: "What Wiped Out the Dinosaurs?" by Edwin Dobb, Scientific American, June 2002, pp. 36-43. This article documents recent discoveries in the Hell Creek Formation (Montana) suggesting significant ecological destabilization leading preferentially to dinosaur declines just prior to the K/T boundary and the asteroid event.

"The Dinosaur Massacre: A Double-Barreled Mystery" by Robert Jastrow, Science Digest, Sept.1983

"The Real Jurassic Park" by Jim Robbins, Discover, March, 1991

"Cretaceous Splashdown" by Tom Waters, Discover, Sept. 1990

"The Dinosaur Acid Test" by Tom Waters, Discover, Feb. 1990

Please note that there are many articles available on this topic, particularly in the early 1980s. Any combination of them can be used effectively. The two suggested are somewhat technical, and may need to be paraphrased to be used with younger students. Teachers may advise students to skim the more technical parts and concentrate on the parts which answer the questions.

USEFUL WEB LINKS:

"What Killed the Dinosaurs?" (Univ. of Calif. Museum of Paleontology)
<http://www.ucmp.berkeley.edu/diapsids/extinction.html>

Then there's this explanation: How Jell-O Killed the Dinosaurs:
<http://www.frankwu.com/Jell-O.html>

Many more recent discussions and evidence can be seen by Googling asteroid dinosaur debate

 ATTRIBUTION

Some of the ideas in this lesson may have been adapted from earlier, unacknowledged sources without our knowledge. If the reader believes this to be the case, please let us know, and appropriate corrections will be made. Thanks.

1. Original Source: unknown (one of the ENSI participants)

2. Reviewed / Edited by: Martin Nickels, Craig Nelson, Jean Beard: 12/15/97

3. Edited / Revised for website by L. Flammer 5/99
Updated 7/2008

1. What happened to the environment of the earth following this disaster that could have caused mass extinctions?

2. What evidence is there to suggest that this catastrophe actually took place?

3. Over how long a time period did these effects take place?

4. What kinds of species became extinct and what kinds of species survived?

First, share your homework answers among the group members.

1. What characteristics do the two "theories" have in common?

2. How are the two "theories" different?

3. Which "theory" does your group accept and why? (This is not an opinion, it should be based on evidence).

4. What does this discussion tell you about the nature of science?