GEOLOGIC TIME: PRINCIPLES & APPLICATIONS

Summary

Average inquiry level: Structured

This inquiry-based lab about the principles of relative and numerical dating allows students to apply reason and logic to determine the order of geologic events, to experimentally create a radioactive decay and ingrowth diagram, and to calculate numerical ages using algebra. This lab is designed for face-to-face instruction.

By the end of lab, students will be able to:

• Determine the order of geologic events using relative dating principles.
• Calculate the age of rocks using numerical dating principles.
• Select correctly from the range of available numerical dating tools to access Earth history at different scales and in different materials.
• Explain how past events from geologic time influence the present and future.
• Demonstrate numerical literacy around units, graph manipulation, and using formulas.

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Context

Audience

undergraduate, introductory, for majors or non-majors

Skills and concepts that students must have mastered

Note: This lab can be placed at any point in the semester - Can add more or less detail to the lab if needed.

Part 1: Familiar with types of dating methods (relative versus numerical).

Part 2: Familiar with fundamentals of the rock cycle (intrusion, sedimentary deposits, contact metamorphism, etc.). Exposure to depictions of Earth in cross section; nature of sedimentary deposits (horizontality and lateral continuity). Familiar with principles of relative dating (basic definitions) and unconformities. Students do not need to be familiar with the Geologic Time Scale, processes of fossilization, or know rock names. Students should know the three rock types.

Part 3: Basic math; Lecture on subatomic particles, ions vs. isotopes, radioactivity, process of radioactive decay; Basic understanding of some common isotopic systems that are geologically useful.

Part 4: Completion of prior parts of lab

How the activity is situated in the course

stand-alone exercise

Goals

Content/concepts goals for this activity

geologic time, relative dating, numerical dating, calculation of dates, radioactive decay

Higher order thinking skills goals for this activity

reasoning and using logic to justify answers, focusing on critical thinking processes rather than a definitive answer

Other skills goals for this activity

searching the internet, working in groups

Description and Teaching Materials

We advise that this lab be printed in color so that cross sections will be easier to interpret.

Part 1. Earth and life history - string of 20 foot length; color printed and laminated cards provided with the activity, cut to ~ 3x5 inches; paper clips; tape to secure the string to the wall

Part 2. Relative Dating - 2 different large rock samples or large color images of outcrops for each lab group. One showing inclusions, another showing a cross-cutting relationship with an event or another rock type (dike; fault). Large color print out or projection of North America Tapestry of Time and Terrain map (available as PDF here: https://pubs.usgs.gov/imap/i2781/)

Part 3. Numerical Dating - Packs of mini M&Ms (30 candies per group); calculator/phone; Dixie cups; paper towels or blank paper

(Optional: rather than using M&Ms, instructors can choose to use different types of candies, such as Skittles, as a precaution for students who may have allergies to chocolate. Another option would be to use pennies or clothing buttons with the sides painted as a different color (ex. one side white, one side black). If this option is chosen, the student handout will need to be updated to reflect the use of non-M&M materials).
Online option: students can use an online coin-flip simulator (example: https://www.random.org/coins/)

Part 4. Conclusions - None.

Materials Provided
a. Student Handouts:
Student lab handout Geologic Time Lab.docx (Microsoft Word 2007 (.docx) 12.7MB Aug16 21) and Timeline Cards distributed to students Timeline cards.pptx (PowerPoint 2007 (.pptx) 45.3MB Aug16 21)
b. Instructor Materials: