8. Extinction Theories - Lesson Plan
- Rather than start class with any warm-up or initial discussion, begin by dividing the class into teams and giving each team a copy of the handout. It is important to keep kids from thinking about what they might have heard previously about the dinosaur extinction 65 million years ago. Many have heard about the catastrophic meteor/asteroid/comet theory and are likely to use evidence to justify their previous beliefs than to use evidence to arrive at a theory.
- Read through the first page of the handout together, stopping to answer any questions and define any vocabulary the students may be unfamiliar with (mass extinction, theory, etc.).
- Emphasize that a theory must be supported by evidence. Encourage students to throw out everything they think they know about the dinosaur extinction and instead seriously consider ANY possible explanation that is suggested by the evidence. The evidence is not equal in importance, so it’s not necessarily the number of evidence cards that matters but the conclusiveness of the evidence that matters. Thus, discourage students from using the strategy of the theory with the most number of evidence cards must be true.
- Students may need an example of what a theory looks like, particularly, the way a theory is composed of a series of logically linked statements. For instance, a theory might say “The dinosaurs, and the majority of other organisms that existed at the time, became extinct because space aliens landed on Earth. An alien virus was released, wiping out all the green life forms including all the dinosaurs and plants. This resulted in the collapse of the food web (since all the producers were wiped out) and an increase in the amount of carbon dioxide in the atmosphere (since plants no longer were using carbon dioxide for photosynthesis).”
- Once students understand the overall goal of this exercise, give them their cards and allow them to begin. Circulate around the room and help groups that get stuck or cannot agree. Make sure that students do not let their previous assumptions interfere with the process and keep students focused on the evidence cards.
- If teams finish early, force them to make their theory as clear as possible and challenge them by pointing out flaws in their logic or evidence that does not fit their ideas. For instance, point out that the Chicxulub crater was formed 300,000 years before the mass extinctions. Force students to think their ideas through completely and explain why they favor some evidence more than others.
- The following class period, or when all groups have finished, give each group a chance to present their theory, and their supporting evidence, to the rest of the class. Allow a question and answer period following each group’s presentation. Make sure that questions from other students are also grounded in the evidence and not personal attacks.
- When all groups have finished, allow an open debate about the causes of the dinosaur extinction. If necessary, clarify the various theories by writing them up on the board. Use this opportunity to discuss what pieces of evidence are stronger than others and why. If it appears that all teams favor one explanation (as happened in one of my classes), play the devil’s advocate and challenge students with evidence supporting an opposing viewpoint. Always come back to the evidence cards and keep the discussion focused on looking for a theory that best explains the evidence at hand.
- 10 minutes before the end of class, close the debate and describe the current state of affairs is in the scientific community – that scientists are very divided into the gradualist and catastrophic camps. Allow students to suggest areas of research that could help settle the debate: more conclusive information about how quickly or slowly the extinctions occurred, more clear evidence of asteroid or meteor impacts, more detailed radioactive dating information, etc.