Earth System Topics: Time/Earth History Show all Earth System Topics: Time/Earth History
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Modeling U-Series Concordia/Discordia Using STELLA
Kirsten Menking, Vassar College
U-Series dating techniques are widely used to determine the absolute ages of some of Earth's oldest rocks, but the concordia/discordia diagram can be quite difficult for students to grasp. I have produced a STELLA-based lab exercise to develop students' understanding of this important chronologic technique. Students create models of the two isotopic decay systems and run these models to create the concordia diagram. They then carry out experiments in which they "add" or "remove" varying amounts of lead or uranium in simulation of metamorphism. In the course of the lab, students are introduced to the concepts of exponential decay and secular equilibrium as well as modeling concepts such as the creation of if-then statements.
Using Dendrochronology to Determine the Age and Past Environments of the Black Forest Region, Colorado, USA
Paul Grogger, University of Colorado at Colorado Springs
The use of dendrochronology in determining the geologic history of a location. The development of an understanding how tree growth can indicate the relationships between climate, geomorphology, ecology and archeology.
Determining Earthquake Recurrence Intervals from Trench Logs
Patricia Cashman, University of Nevada-Reno
Trench logs of the San Andreas Fault at Pallett Creek, CA are the data base for a lab or homework assignment that teaches about relative dating, radiometric dating, fault recurrence intervals and the reasons for uncertainty in predicting geologic phenomena. Students are given a trench log that includes several fault strands and dated stratigraphic horizons. They estimate the times of faulting based on bracketing ages of faulted and unfaulted strata. They compile a table with the faulting events from the trench log and additional events recognized in nearby trenches, then calculate maximum, minimum and average earthquake recurrence intervals for the San Andreas Fault in this area. They conclude by making their own prediction for the timing of the next earthquake.
Roping Geologic Time
Randall Richardson, The University of Arizona
After having talked about the geologic time scale, I ask for two volunteers from the class to hold a rope that is 50 feet long. I say that one end is the beginning of the Earth (4.6 billion years ago), and the other is today. I then give out 16 clothes pins and ask various students to put a cloths pin on the 'time line' at various 'geologic events'. Throughout the activity I have a quiz going on where the students calculate percentages of Earth History for major geologic events, and compare it to their own ages. On their time scale, the dinosaurs died only about two 'months' ago! The exercise is very effective at letting them get a sense of how long geologic time is, and how 'recently' some major geologic events happened when you consider a time scale that is the age of the earth.
Ocean Crust Ages Lecture Tutorial
Karen Kortz, Community College of Rhode Island; Jessica Smay, San Jose City College
Students work on this Lecture Tutorial worksheet on ocean crust ages in groups during lecture. It directly confronts misconceptions students have about the patterns of ages of the ocean crust, and interpretations that can be made.