Relative Geologic Time and the Geologic Time Scale

Bret Bennington

Hofstra University

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Initial Publication Date: August 27, 2009 | Reviewed: June 24, 2014 (see revision history: 2 events)

Summary

Group simulation of the development of the geologic time scale illustrating concepts of correlation and relative time. Extremely effective for teaching the significance of the geologic time scale.

Historical Geology, Biostratigraphy/Biogeography | College Introductory, College Lower (13-14)

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Context

Audience

I use this activity in my Introduction to Historical Geology course and my Introduction to Dinosaurs and the Mesozoic World course. Useful in any course where students encounter geologic time for the first time.

Skills and concepts that students must have mastered

None really, although a brief introduction to fossils and strata is helpful (I use the Grand Canyon to illustrate these).

How the activity is situated in the course

Usually the first activity I do in class.

Goals

Content/concepts goals for this activity

Superposition, correlation using fossils, relative time, origin of the peculiar period names in the geologic time scale, and significance of fossils and evolution for providing a biological calendar of Earth history.

Higher order thinking skills goals for this activity

Students are asked to explain why their is a gap in time in the strata of the Grand Canyon but no physical gap in the rock layers.

Other skills goals for this activity

Group activity that helps "break the ice" at the beginning of a course.

Description of the activity/assignment

Students are given a short introduction to fossils, strata, Steno's law of superposition, and the development of the geologic time scale from initial description of systems, through the realization that fossils could be used to correlate between systems, to the assembly of the modern geologic time scale. Then, each student in the course is given a sheet of paper with a simple stratigraphic column and associated fossils representing a geologic system on one side and a short description of the location and history of discovery of the system on the other. On a large wall, students then assemble four geologic columns from their systems representing mainland Europe, Great Britain, the Eastern U.S. and the Western U.S. using the fossils illustrated on their sheets to correlate systems. The instructor guides this process by placing the first system on the wall and by providing some narration as the columns take shape. Europe and Great Britain are assembled first, one sheet at a time, providing when completed the framework of the modern geologic time scale. Once this is up on the wall, the remaining students can assemble the other two columns in minutes using fossils to correlate between American and European systems. A temporal gap in the Grand Canyon sequence provides an opportunity to discuss the incompleteness of the rock record in any one place and a system composed of igneous and metamorphic rocks with no fossils is used to point out the difference between radiometric (absolute) and biostratigraphic (relative) dating.