Controversies in the Earth Sciences

Exploring a controversial theory


In this next activity, we'll concentrate on the relatively new and controversial theory that an asteroid impact caused the Permian/Triassic extinction event. By doing this, I admit that I'm deliberately not spending time on the other theories that have more adherents, such as the theories that Lee talked about in the video on the previous page. First, I want us to talk about impacts in general this week. Second, this gives us a way to compare what the state-of-the-art thinking is with respect to extraterrestrial impacts for the Permian/Triassic extinction while the evidence for an impact at the K/T boundary is still fresh in our minds.

We will not discuss the papers below as part of a graded discussion. Please do read them because some of the knowledge you get from them will help inform you when you work on the impact craters problem set Cross-out refers to what we did last time I taught this course. I left it in instead of deleting it so you can see what the assignment was. I alternate between discussing the K/T and the P/Tr each time I teach this class.

Reading/Discussion Assignment


  1. I have divided up the relevant reading material for this activity into two sets. Each set contains one scientific paper, as well as press releases, summaries, and/or comments from other scientists that are directly related to that paper. First, find your teams and then read each of the popular press articles and each scientific paper designated for your team. You will see that there are specific questions that go along with each set of readings, which you will be addressing in the discussion component of this activity. I want you to know the arguments the authors make without getting bogged down by technical details. I suggest keeping track of terminology or technical details that are confusing to you and post them to your team's discussion board. This looks like a lot of reading at first glance, but the articles aren't too long. You will engage in a team discussion of your team's set of papers in the "Lesson 3 - Permian/Triassic Extinction" team discussion forums. (See "Submitting your work" below)
  2. Next, skim the discussions that went on in the other team's forum so that you are acquainted with all of the reading material. You can ask them questions if there's something you don't get!
  3. Then, engage in a class discussion of these hypotheses, which will take place in the "Lesson 3 - Permian/Triassic Extinction" class discussion forum. (See "Submitting your work," below.)

    Special note to Group-Work-Haters: I am dividing you up in teams because I have assigned more reading than I think each of you can be expected to process on your own. So, each of you only has to read half of it. Therefore, the job of the group discussion is to clarify your thinking about the papers and also to provide an overview to the other team, through your discussion, of the content of the papers you read.

    Team 1

    1. SCIENTIFIC PAPER - Becker, L., Poreda, R. J., Hunt, A. G., Bunch, T. E., & Rampino, M. (2001). Impact event at the Permian-Triassic boundary; evidence from extraterrestrial noble gases in fullerenes. Science, 291(5508), 1530–1533.
    2. PRESS RELEASE - Kerr, R. A. (2001). Whiff of gas points to impact mass extinction. Science, 291(5508), 1469–1470.
    3. Farley, K. A., Mukhopadhyay, S., Isozaki, Y., Becker, L., & Poreda, R. J. (2001). An Extraterrestrial Impact at the Permian-Triassic Boundary? Science, 293(5539), 2343a. doi: 10.1126/science.293.5539.2343a.


    1. What's a fullerene and what's the connection between fullerenes and an extraterrestrial impactor?
    2. Evidence for an impact is different in this case than for the K/T boundary impact.How and why?
    3. How is the size of the asteroid estimated from the He data? Could you follow the logic here?
    4. What are the objections raised by Farley and Isozaki?How does Becker's group reply to the objections?Which do you find more compelling?What should be done next to try to settle this debate?

    Team 2

    1. SCIENTIFIC PAPER - Becker, L., Poreda, R. J., Basu, A. R., Pope, K. O., Harrison, T. M., Nicholson, C., et al. (2004). Bedout; a possible end-Permian impact crater offshore of northwestern Australia. Science, 304(5676), 1469–1476.
    2. PRESS RELEASE - Science and Technology: Bang and blame; The end of the Permian. (2004).The Economist,371(8375), 89.
    3. Wignall, P., Thomas, B., Willink, R., Watling, J., & al, E. (2004). Is Bedout an Impact Crater? Take 1/Response. Science, 306(5696), 609.
    4. Renne, P. R., Melosh, H. J., Farley, K. A., Reimold, W. U., et al. (2004). Is Bedout an Impact Crater? Take 2/Response. Science, 306(5696), 610.
    5. Glikson, A. (2004). Comment on "Bedout: A Possible End-Permian Impact Crater Offshore of Northwestern Australia". Science, 306(5696), 613b. doi: 10.1126/science.1100404.
    6. Becker, L., Poreda, R. J., Basu, A. R., Pope, K. O., Harrison, T. M., Nicholson, C., et al. (2004). Response to Comment on "Bedout: A Possible End-Permian Impact Crater Offshore of Northwestern Australia". Science, 306(5696), 613c. doi: 10.1126/science.1103906.
    7. Dalton, R. (2004). Comet impact theory faces repeat analysis. Nature, 431(7012), 1027.


    1. Assuming that Becker's arguments are true about the P/Tr extinction having been caused by an impact, what is the evidence in favor of Bedout as the crater location for that impact?
    2. What is the evidence against Bedout as the crater location for the end-Permian extinction?
    3. What parts of this story of the hunt for the crater are similar to the Chicxulub story and what parts are different?

    Class discussion


    1. Why do you think the impact theory is popular for the K/T extinction but not for the P/T?
    2. The previous lesson in this course dealt with a controversy that involved both science and public policy because it concerned hazard mitigation. In this case, the debate is really just scientific. (i.e., nobody on this planet faces some immediate danger if we can't pin down a kill mechanism for the P/T extinction). Does that fact change the way you approach your thinking about it? Does it seem like it changes the way the scientists who wrote these articles approach it?

    Submitting your work

    You will need to participate multiple times during the discussions.

    1. Enter your team's forum of the "Lesson 3 - Permian/Triassic Extinction" team discussion forums (there is one for each reading set).
    2. You will see the discussion questions posted there.
    3. Respond to one question that hasn't already been chosen by another student. If all questions have already been addressed, then select a question where you can further the discussion and post there.
    4. Return to the discussion periodically to read your classmates postings and to respond by asking for clarification, asking a follow-up question, expanding on what has already been said, etc. week 2 of this lesson
    5. After the team discussion period ends, read the discussion threads in the other team's forum. If you can't get the gist of the articles they read, ask them some questions until you have a clearer picture.
    6. Enter the "Lesson 3 - Permian/Triassic Extinction" class discussion forum.
    7. Repeat steps 2-4 above. week 3 of this lesson

    Grading criteria

    You will be graded on the quality of your participation, both in your team discussion and in the discussion involving the whole class. See the grading rubric for specifics on how this assignment will be graded.

    Optional further reading

    The articles below are press releases that accompanied scientific papers that detail other theories for the end-Permian extinction event. Check them out: