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Just-in-Time Teaching (JiTT) WarmUp Activity: Cambrian Explosion

Laura Guertin, Penn State University Delaware County
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1) How do scientists come up with the number 2 billion years ago for the first branch of life? Explain the dating technique and information that is used.

2) Describe the evidence AGAINST the Cambrian Explosion. What are the assumptions that go along with this?

3) Based on the readings/lectures/and your own "gut instincts," what do you believe was the trigger "responsible for a huge expansion in size, complexity and body architecture of animals and all of the major animal phyla in existence today"?

Student Responses:

See the Just-in-Time Teaching page on assessment for information and ideas on how to evaluate student responses.

References and Notes:

Articles that students may be assigned to read for this set of questions include (but are not limited to):

Wilford, J.N., "First branch in life's tree was two billion years ago." The New York Times Book of Fossils and Evolution, p. 100-103.

Wilford, J.N., "Using genes as a clock, study traces animal life back a billion years." The New York Times Book of Fossils and Evolution, p. 104-107.

The use of Just-in-Time Teaching is discussed in detail on the JiTT Starting Point page.

Additional information on JiTT is available in the book:


Geoscience:Geology:Historical Geology

Resource Type

Activities:Classroom Activity:Just in Time Teaching

Grade Level

College Lower (13-14):Introductory Level

Ready for Use

Ready to Use

Earth System Topics

Time/Earth History


Teach the Earth:Teaching Environments:Intro Geoscience