EARTH 501
Controversies in the Earth Sciences

Lesson 3: Mass Extinctions: Consensus in the Craters?

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The figure below shows a simplified geologic cross-section of an impact crater in Chicxulub, Mexico. This crater is thought by most scientists to be the impact crater resulting from the asteroid collision that caused the mass extinction event at the end of the Mesozoic era about 65 million years ago. In this lesson we will discuss prevailing hypotheses for this and other mass extinction events during Earth's history. We will also discuss the effect on evolution/diversification of life following mass extinction events.

geologic cross section of the crater at Chicxulub
Archived by WebCite® at http://www.webcitation.org/5VdFMykv2
Kring, David A. TITLE. NASA/University of Arizona Space Imagery Center. 2008-02-15. URL:http://www.lpl.arizona.edu/SIC/news/Chicxulub_drilling_hires.jpg. Accessed: 2008-02-15.

About Lesson 3

I think the subject matter of this lesson is an important educational topic for two reasons. The first is that any discussion of the pattern of evolution, diversification, and extinction of life on Earth over geologic time must necessarily bring up the subject of deep time and the age of our planet. The age of the Earth is not at all a controversial subject among scientists, but recently in the United States, public schools have been pressured to teach "alternative explanations" that have no scientific merit. The second reason is that the subject of mass extinction events ties together the disciplines of geology and biology; it is an important part of teaching and learning science to recognize that scientific disciplines are linked, even though they are usually taught in schools as completely separate fields.

photo of a signpost on which strange but pro-evolution thoughts are pasted.
Waves solidified into hydrogen atoms? Another good reason why the world needs more science teachers. I took this photo near the Circo Massimo in Rome.
(Photo: E. Richardson)

What will we learn in Lesson 3?

By the end of Lesson 3, you should be able to:

  • List the evidence for an extraterrestrial impactor at the K/T boundary
  • List other hypotheses that have been proposed for the K/T extinction
  • List the evidence for an extraterrestrial impactor at the end-Permian extinction
  • List other hypotheses that have proposed for the end-Permian extinction
  • Explain the difficulties of finding ancient impact sites
  • State how often the Earth is hit by extraterrestrial objects of various dimensions
  • Describe the aftermath of an asteroid strike (i.e., immediate and long-term environmental effects)
  • Describe the effect on evolution/diversification of life following mass extinction events
  • State the ages of the K/T extinction event and the end-Permian extinction event
  • State the age of the Earth and why we know this is true

What is due for Lesson 3?

Lesson 3 will take us three weeks to complete. 8-28 Feb 2017.

The chart below provides an overview of the assignments for Lesson 3. There are two problem sets and two discussions. One of the problem sets is broken into two parts (each part with a different due date). One of the discussions is a jigsaw activity in which you will first discuss scientific papers with a small group,and then with the whole class.

Lesson 3 assignments
Requirement Submitted for grading? Due date
Reading: An introduction to recent debates No

14 Feb

Problem set: Antipodes and Geologic Time, part 1

Yes—Submitted to the "Antipode and timescale problem set part 1" assignment in Canvas

14 Feb

Problem set: Antipodes and Geologic Time, part 2 Yes—Submitted to the "Antipode and timescale problem set part 2" assignment in Canvas 21 Feb
Reading: The K/T extinction event No 21 Feb
Reading / Discussion: Exploring a controversial theory—the Permian/Triassic Extinction Yes-Graded group discussion in Canvas participation spanning 15 - 21 Feb (2nd week)
Reading / Discussion: Exploring a controversial theory—the Permian/Triassic Extinction Yes-Graded whole class discussion in Canvas participation spanning 22 - 28 Feb (3rd week)
Problem set: Correlating impacts and extinctions Yes—Submitted to the "Impact craters problem set"assignment in Canvas 28 Feb
Reading: Recovering from an extinction No 28 Feb
Discussion: Teaching and learning about mass extinctions Yes—Graded discussion in Canvas participation spanning 22 - 28 Feb (3rd week)

Questions?

If you have any questions, please post them to our Questions? discussion forum (not e-mail). I will check that discussion forum daily to respond. While you are there, feel free to post your own responses if you, too, are able to help out a classmate.