Unit 2: Causes of Mass Extinction
During Unit 2, students will learn about the causes of two past mass extinctions and discuss the controversies surrounding these causes and the evidence upon which the theories in the debates are based. Before class, students will be assigned to read one of a set of different articles about theories for the causes of the end-Cretaceous and the end-Permian mass extinction. During class, students will get in groups with others who read different articles to pool their knowledge about flood-basalt eruptions and catastrophic asteroid impacts. They will re-group to compare and contrast the two proposed causes of the end-Permian and end-Cretaceous mass extinctions and the mass extinctions themselves.
By the end of the unit, students will be able to:
- Explain how the effects of either flood basalts or meteor impacts could cause a mass extinction.
- Describe evidence for flood-basalt eruptions or massive impacts at the end of one of the ancient mass extinctions.
- Describe the probable effects of a flood-basalt eruption or a massive impact.
- Compare and contrast the end-Permian and end-Cretaceous ancient mass extinctions.
Overarching Module Goals
- Use of data: This unit stresses the challenge of interpreting evidence (when it is available), but students are not directly working with measurements.
- Interdisciplinary and system-based problem-solving: Flood basalts and massive impacts can be both directly and indirectly lethal because of their effects on Earth's systems such as the atmosphere and hydrosphere, so the students will explicitly discuss these.
- Big Ideas of Earth Literacy: This unit addresses Big Idea #1 (the use of observations in science), #3 (Earth's systems), #4 (continuous change), and #6 (evolution of life explicitly). It addresses #2 (the age of Earth), #5 (its status as a water planet), and #8 (the danger that natural hazards pose to humans) implicitly.
Context for Use
This unit is the second of a series of five lessons in the Changing Biosphere: Lessons from the Past Module. It can be used in almost any size of class, but students need to be able to talk to one another. It is designed for a 50-minute class period.
In order to participate, students need to do a reading before the class in which the jigsaw exercise takes place (learn more about Jigsaws). If the instructor expects that some students will not do their assigned reading, the students should take a reading quiz before that class, and an alternate assignment should be available for those who do not pass.
Before class, either assign the students who have passed the reading quiz into SuperTeams (at least one student each from reading groups A, B, C, or D; try to avoid creating groups larger than five students), or have a list of those who have passed and have them sort themselves into SuperTeams.
Description and Teaching Materials
Break students into topic groups and assign different readings. Give all students the Unit 2 - Student Worksheet - MS Word (Microsoft Word 2007 (.docx) 61kB Dec27 16)/Unit 2 - Student Worksheet - pdf (Acrobat (PDF) 118kB Dec27 16) to help guide their reading and to prepare them to run the discussion. Also give them access to the Unit 2 Study Guide (Vocabulary) (Microsoft Word 2007 (.docx) 16kB Jan19 17)/Unit 2 Study Guide (Vocabulary) - pdf (Acrobat (PDF) 93kB Jan19 17). Each article is approximately 2000 words and should take less than half an hour to read.
- Group A will read about flood-basalt eruptions at the Deccan Traps at the end of the Cretaceous (Acrobat (PDF) 319kB Apr3 17)
- Group B will read about flood-basalt eruptions at the Siberian Traps at the end of the Permian (Acrobat (PDF) 319kB Apr3 17)
- Group C will read about the impact at Chicxulub about the end of the Cretaceous (Acrobat (PDF) 340kB Apr3 17)
- Group D will read about possible end-Permian impacts (Acrobat (PDF) 340kB Apr3 17)
Students take a brief quiz (either online before class or at the start of class) to indicate that they completed and understood the reading . If it is being graded and administered before class, it could be taken electronically through a class management system (CMS) like Blackboard or Moodle. One advantage to electronic CMS quizzes is that students can be given multiple (even unlimited) chances to take them to get a passing score.
There is a different quiz for each reading group (all of the following are for instructor only):
This exercise depends on student participation and that in turn will depend on student preparation. Since all of the students in a group have different readings, a group with an unprepared student will not have access to the information it needs to complete its task. As instructor, you will need to decide how to assess student readiness. You will need to make your criteria for readiness clear to the students before the assessment. For example, if you are giving students a quiz that they can take online an unlimited number of times using their notes and the original article, you might tell them that they will need a score of 80% or more on one of those attempts to pass. It is up to you if you want to count the score as a grade. You should remind them that their quiz performance will allow you to put people who have done the reading into the same discussion groups (it is also in the handout).
On the day of class, students should bring their worksheets, writing implements, and either a copy of the article or their notes. Depending on the arrangement of your classroom, you may want to distribute clipboards with the worksheets.
The simplest (at least in a small class or one with consistently high attendance) is for the instructor to assign students to SuperTeams (consisting of at least one student from each reading group, but no larger than five students if possible) before class. In a large class where people are often absent or late, the instructor will need to come to class with a list of the students broken up by reading group and whether they passed their reading quiz and then assemble SuperTeams quickly at the start of class. You do not need to tell the whole class who has passed the quiz (even if it is not graded). Just place students who have passed the quiz together on one set of SuperTeams, the ones that should be able to complete the exercises, and place those who have not in a different set, ones that will at least work on the exercises if they have access to the readings that they were supposed to do. If the unprepared students do not have access to their articles in the classroom and did not bring a printout, you can decide whether to give them another project to work on.
In a large class with low average attendance, it is easier to let the students form their own SuperTeams at the beginning. This runs the risk of prepared students struggling to complete the exercise because they have an unprepared student in the group who is the only one with access to one of the readings. To encourage preparedness, enforce individual accountability with grades: both for the reading quiz beforehand, and participation points, assigned by the group using a Peer-Assessment Form - MS Word (Microsoft Word 2007 (.docx) 12kB May16 16)/ Peer-Assessment Form - pdf (Acrobat (PDF) 93kB May16 16). When you initially assign the articles, remind the students of these grades. In class, have each student put his/her reading-group code (A,B,C, or D) on a piece of paper and hold it out so that others can see it and round up a group with at least one of each letter (but no more than five if possible). Alternatively, if you have printed out their readings for them previously, make sure to print each article (red for the article on the Deccan Traps, blue for the article on the Chicxulub Impact or whatever is available) and have the students find appropriate group members that way.
If anyone in class has visual impairments or cannot move around the classroom quickly, allow them to remain in place, and have other students go to them to form groups. Students who arrive after step 1 has started may have a difficult time catching up if placed in groups with students who have done the reading. If you know that the late student is well prepared for the exercise, you could add him or her to a SuperTeam with other prepared students as a fifth member.
In-Class Exercise (45-50 min)
If you have a computer attached to a projector, you can post the Unit 2 Presentation (PowerPoint 2007 (.pptx) 734kB Dec27 16)/Unit 2 Presentation (pdf) (Acrobat (PDF) 677kB Dec27 16), but it is just a summary of what is on the Unit 2: Student Discussion Guide (MS Word) (Microsoft Word 2007 (.docx) 61kB Dec27 16)/Unit 2: Student Discussion Guide (pdf) (Acrobat (PDF) 118kB Dec27 16). Do not spend class time reading this aloud to them.
Most of the class (at least 35 min), will be student-centered. The instructor's job will be to keep track of time and to facilitate by moving among groups, answering questions, and prompting student discussion if it wanders off track or seems incomplete. The
If students who did not do the reading carefully before class have access to their articles, they can start reading and fill in the answers to the questions in step 1 on their own, and they can try to do the Venn diagrams with other students who have been assigned to work with them. Alternatively, have them trade articles with the students who they would ordinarily be paired with and read those instead.
At the end of the third step, the instructor starts talking to the class as a whole. Ask one group to explain how the end-Cretaceous and the end-Permian extinctions were similar and how they were different (or split it up among multiple groups). You may need to ask other groups to add to the explanation (10 min, or fewer if the initial grouping process made the earlier part of the lesson take more than 35 min).
At the end, if any time is left, tell the students that there are other theories to explain mass extinction, such as disease epidemics or radiation bursts from supernovas, but that these are hard for science to tackle, because we are not sure what kind of evidence they would leave behind.
At your discretion, you can assign a short homework assignment (Unit 2 Homework (MS Word) (Microsoft Word 2007 (.docx) 15kB Jan17 17) /Unit 2 Homework (pdf) (Acrobat (PDF) 43kB Jan17 17) ) asking students about their own assessments of the evidence discussed in this lesson. The instructor can collect these (or a random sample of them in a large class) to see whether the students engaged with the material that they read and discussed (Guidelines for Grading Homework (MS Word) (Microsoft Word 2007 (.docx) 12kB Jan19 17)/ Guidelines for Grading Homework (pdf) (Acrobat (PDF) 55kB Jan19 17)). It will take 5 to 15 minutes depending on other things that the student is doing at the time.
Likewise, especially if the students chose their own SuperTeams, ask them each to fill in a Peer-Assessment Form - MS Word (Microsoft Word 2007 (.docx) 12kB May16 16)/ Peer-Assessment Form - pdf (Acrobat (PDF) 93kB May16 16) on paper or online through the CMS and to turn them in at the start of the next class for participation points.
Teaching Notes and Tips
This lesson is a jigsaw, a form of cooperative learning in which students work together to master part of the content of a lesson, then teach each other. It is student-centered, so the instructor does not lecture (except possibly for a few minutes at the end), but facilitates student discussion.
If this unit is being taught as part of a course or module about the current mass extinction, the students could compare and contrast the ancient mass extinctions with the current (sixth) mass extinction.
Assessment on Student Reading (all of the following are for instructor only):
- If you want to give these quizzes to the different groups to persuade the students to do the reading carefully before class, administer them online through your course management system or have them do the appropriate quizzes as homework.
Consider using the discussion questions as short-essay exam or homework questions:
Learning Outcome #1:
- Explain, using cause-and-effect language, how either a flood-basalt eruption or the impacts of a large (6+ km-long) meteor could cause a mass extinction, specifically either the end-Permian or the end-Cretaceous mass extinction.
Learning Outcome #2:
- Describe evidence that indicates whether flood-basalt eruptions and impacts occurred at the end of either the Permian or the Cretaceous and where they happened.
Learning Outcome #3:
- How does the end-Permian mass extinction differ from the end-Cretaceous mass extinction in terms of causes, effects of those causes, and evidence for those causes?
- How does the end-Permian mass extinction resemble the end-Cretaceous mass extinction in terms of causes, effects of those causes, and evidence for those causes?
Instructors should consider modifying questions and setting standards for answers to best reflect the levels and emphases of their courses. Here is the
References and Resources
- Earth Impact Database — A list of all of the verified impact craters discovered to-date on Earth and links to pages with information on meteors, impacts, and craters.
- Impact Earth (Purdue's impact simulator) — The user inputs the diameter and density of the meteor, angle and velocity of impact, distance from impact, and the environment in which the crater forms (the site makes some suggestions about likely ranges), and the program describes likely effects of the impact, including a description of the crater, the amount of energy released, airblast and thermal radiation at the location chosen, etc.