Finding the Missing Half T-Rex (a study of faults)
In this structural geology activity, students are faced with a particular scenario: determine the whereabouts of the missing half of a fossil T-Rex skeleton that has been cut in half and offset by a fault. In order to solve this problem, students systematically manipulate a set of wood blocks, discovering the general rule that the beds on the uplifted side of a fault appear to migrate in the direction of their dip. This discovery allows the students to locate the missing half of the T-Rex and write a logical rationale for their solution.
By working through this activity, students deepen their understanding of basic structural geology concepts, develop their 3-D visualization skills, practice using inductive reasoning to come to a general conclusion, practice using deductive reasoning to apply a general rule to a specific problem, and improve their scientific writing skills.
The specific content learning objectives are:
- Thoroughly understand and be able to use basic structural geology terms:
- strike and dip
- hanging wall and footwall
- strike-slip fault and dip-slip fault
- right-lateral and left-lateral fault
- normal, reverse and thrust fault
- Be able to distinguish a normal fault from a thrust or reverse fault by examining the offset of dipping beds across the fault.
Context for Use
This lab activity can be used in a wide range of courses. At California State University, Chico, we use this activity in our Physical Geology and Structural Geology courses. Wendy Van Norden uses this activity in her honors geology class at Harvard-Westlake high school in North Hollywood. Before completing this activity, students should be introduced to basic geologic maps and cross sections, the concept of strike-and-dip, and the classification of faults.
Description and Teaching Materials
- Student Handout for the Missing T-Rex Structural Geology Activity
- Microsoft Word Format (Microsoft Word 360kB Sep9 09): The geologic map on page 2 does not show or print correctly if you print this file directly from Microsoft Word; the fill patterns do not show. I don't know why. From my computer, if I save this file as a .pdf and THEN print it from Adobe Acrobat, the patterns show. (I don't know why; I just accept it and don't ask any questions.)
- Adobe Acrobat Format (Acrobat (PDF) 86kB Sep10 09): The geologic map shows and prints perfectly from this file format, but you can't easily modify the file.
- You will also need one set of blocks per lab table: Plans for constructing the blocks (Microsoft Word 93kB Dec17 08).
- Geologic Map and Cross Section (Illustrator 316kB Dec17 08) (Adobe Illustrator Format): For those folks who have Adobe Illustrator version CS2 or higher, and wish to make alternate versions of the map. Handy for quiz or exam questions.
- An answer key for this activity is available upon request from abykerk-kauffman AT csuchico.edu.
Teaching Notes and Tips
This lab activity takes one to two hours to complete. Students often start by diving right in and trying to draw the cross section and solve the missing-half T-Rex puzzle. A few students are capable of this; most spin their wheels and get frustrated. I always find myself encouraging the students to follow the steps as laid out in the handout, answering the questions one at a time, and trusting that these questions will lead them where they're trying to go. Once students start answering the questions, they move along well with little help until they have completed their table of different possible cases and are asked to use inductive reasoning to come to a general conclusion. At this point, there are a couple of sticking points that students often need help with. They tend to have trouble seeing which of the two columns of the table are identical. Once they see it, they also have trouble choosing the statement that best summarizes this finding; it helps to point out the difference between what appears to happen and what actually happens. A final word of caution: students are sorely tempted to draw dinosaurs on the wood blocks, ruining the activity for future classes. I have given up trying to prevent them from doing this. Instead I supply water-soluble overhead transparency pens for this purpose; the ink washes right off if you do it immediately after class (assuming you have coated the wood blocks with a couple of coats of polyurethane varnish).
I rarely grade this entire activity. Instead, I ask students to take it home and to write a well-written essay that explains and clearly justifies their solution to the problem. I ask them to illustrate this essay with the completed geologic map and cross section.
Another very good way to assess student learning from this activity is to present the same problem with bedding and/or the fault dipping in a different direction and/or with the opposite apparent sense of fault offset in map view. This can be presented as a ConcepTest question, quiz, exam problem, homework assignment, or oral presentation (each lab group could be assigned to a different case, for example).
References and Resources
GeoBlocks 3-D (more info)
, by Stephen J. Reynolds, Arizona State University. Excellent interactive QuickTime Virtual Reality movies exploring the three-dimensional nature of geologic structures.