Relative and Absolute Geologic Time with Maps and Spreadsheets
Skills and concepts that students must have mastered
How the activity is situated in the course
Content/concepts goals for this activity
Higher order thinking skills goals for this activity
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Description of the activity/assignment
Much of what we know about the geologic history of Earth is based on information in rocks now exposed at Earth's surface. Research into Earth history is much like research into human history, but instead of searching through accounts written on sheets of paper as historians do, geologists examine layers of rock. Relative dating of geologic features involves putting geological events in a correct time sequence from oldest to youngest. Absolute dating yields a number (years or Ma = mega-anna = millions of years). In this exercise, students learn and apply the concepts geologists use to determine the relative and absolute ages of rocks.
Student materials for this exercise include a Microsoft Excel spreadsheet with with data for radioactive decay and isotopic dating and an MS Word instruction sheet. The exercise is divided into three parts.
In Part I, students study stratigraphic principles and use them to interpret both a map and a vertical cross section. The Geologic Column is introduced in relative terms.
Part II involves calculating the fractions of parent and daughter isotopes in samples using the equation for radioactive decay and the decay constants for three isotopic systems (40K-40Ar, 238U-206U, and 14C-14N). Students also graph their results and interpret the graphs in terms of half-life and decay constants.
In Part III, students calculate isotopic ages for three rocks, bracket the ages of undateable rocks, and interpret the Geologic Time Scale in absolute terms.
Determining whether students have met the goals
Teaching materials and tips
- Activity Description/Assignment: Student Instructions for Geologic Time Acitivty (Microsoft Word 2007 (.docx) 5.6MB Jun17 19)
- Instructors Notes: Instructors Notes for Geologic Time Activity (Acrobat (PDF) 3.4MB Jun17 19)
- Student Workbook for Geologic Time Activity (Excel 2007 (.xlsx) 1MB Jun17 19)
- Europa Poster for Geologic Time Activity (Acrobat (PDF) 845kB Jun17 19)
Valley, J.V., et al., 2014, Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography: Nature Geoscience, vol. 7, pp. 219-223. Online resource – Accessed 17 June 2019
GSA Geologic Time Scale, 2012: Online resource – Accessed 17 June 2019
Harwood, R., 2017, Relative Dating Exercise: Online resource – Accessed 17 June 2019
Urban, T., 2013, Putting Time into Perspective: Online resource – Accessed 17 June 2019