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Geosciences LibreTexts

3.1: Overview

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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.

    Figure 3.1: Geologica cross-section of the crater at Chicxulub. Archived by WebCite®

    Kring, David A. TITLE. NASA/University of Arizona Space Imagery Center. 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.

    Figure 3.2: 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.

    Click for a text description Figure 3.2.

    (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 three weeks to complete. 18 Sep - 8 Oct 2019.

    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).

    Lesson 3 assignments

    Requirement Submitted for grading? Due date
    Reading: An introduction to recent debates No 24 Sep
    Problem set: Antipodes and Geologic Time, part 1 Yes—Submitted to the "Antipode and timescale problem set part 1" assignment in Canvas 24 Sep (end of week 1)
    Problem set: Antipodes and Geologic Time, part 2 Problem set: Antipodes and Geologic Time, part 2 1 Oct (end of week 2)
    Reading: The K/T extinction event Yes-Graded discussion in Canvas participation spanning 25 Sep - 1 Oct (2nd week)
    Reading / Discussion: Exploring a controversial theory—the Permian/Triassic Extinction Yes-Graded group discussion in Canvas 1 Oct (end of week 2)
    1 Oct (end of week 2) Yes—Submitted to the "Impact craters problem set" assignment in Canvas 8 Oct (end of week 3)
    Reading: Recovering from an extinction No 8 Oct
    Discussion: Teaching and learning about mass extinctions Yes—Graded discussion in Canvas participation spanning 2 - 8 Oct (3rd week)


    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.