The Proterozoic Fossil Record

Julie K. Bartley
,
Gustavus Adolphus College


Summary

In this specimen-based activity, students examine microfossils and stromatolites and build an understanding of the Proterozoic paleontological record.

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Context

Audience

Introductory historical geology course or undergraduate paleontology course.

Skills and concepts that students must have mastered

Basic modes of fossilization; survey of sedimentary rock types; rules for sketching hand samples

How the activity is situated in the course

Second laboratory exercise in the "fossil record" portion of the historical geology lab; in a paleontology course, this activity would be combined with other pieces examining the microfossil record of the Proterozoic

Goals

Content/concepts goals for this activity

Conceptualization of an environment dominated by microorganisms (the Proterozoic), and particularly to understand the differences between the environment at a single time slice (e.g., seafloor at a point in time) vs. the geologic structure produced over time (e.g., accumulated layers of a stromatolite).

Higher order thinking skills goals for this activity

Analysis of spatial data: relationship between 2-D and 3-D structures. Evaluation of the importance of variables in producing observed structures.

Other skills goals for this activity

Writing: brief descriptions of observations, posing hypothesiss. Drawing: creating simple representations of complex rock structures.

Description of the activity/assignment

In this laboratory exercise (2 hours), students explore the Proterozoic fossil record by examining two samples of microfossils, preserved in chert) and numerous samples of stromatolites. The laboratory exercise coincides with lecture discussions on the early history of life, and serves to illustrate the paleontological record of the Proterozoic. This exercise is the first laboratory exercise in the course that asks students to engage with and speculate upon the environmental and biological causes of the observed fossil record. The students' goal is to be able to identify some of the main environmental factors that combine to produce the diversity of stromatolite forms.

Determining whether students have met the goals

Students have conversations during the lab exercise, in which they propose hypotheses to explain their observations about stromatolites. Students hand in the product of their exercise and it is evaluated. Finally, students answer questions about stromatolite construction and microfossil preservation on the midterm exam.

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