Greenstone Belt Assessment
Glendale Community College (AZ)
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Students examine and describe rocks found as part of a geologic sequence formed during the Precambrian Era and determine the geologic significance of each of the rocks in order. The capstone (not included on the worksheet) is tying these rock descriptions together to describe the possible plate tectonic history of these regions.
GLG102 - Introduction to Historical Geology; Non-majors course with no pre-requisite. The first quarter of the class reviews the basic concepts of GLG101 in order to have students who have and have not taken prior geology courses on the same footing.
Skills and concepts that students must have mastered
Prior to this exercise, students have examined all the major rock types and had labs where these rocks have been described and named. Some of the rocks in the sequence have been described in more detail than others. Students have studied relative dating techniques that make the order of age relationship clear. Students have a basic understanding of plate tectonic boundaries and the minimum geologic evidence we must have to verify the past existence of a plate boundary.
How the activity is situated in the course
This is used as an in-class project over the course of approximately one hour and fifteen minute class period, depending on questions and detail of work for the particular group of students.
Content/concepts goals for this activity
- Determining how relative dating of rocks can also extend to relative dating of major earth processes and changes (i.e., presence of pillow basalts lending evidence for the presence of surface water)
- Connecting various geologic features and their relevance to hypothesize about the presence of past large-scale geologic change (i.e, plate boundaries, etc.)
- Outline of the evolution of some of the Earth system's earliest changes
Higher order thinking skills goals for this activity
- Formation of hypothesis regarding ancient plate model while synthesizing extensive data.
- Utilization of prior knowledge to expand application to particular examples and using them to describe Earth processes.
Other skills goals for this activity
- Students work in pairs or groups to examine the rocks and complete the chart, so cooperation between the partners and merging of what they each remember from earlier in the course is involved.
Description of the activity/assignment
This lab utilizes rock samples and images of rocks found in Greenstone Belts that formed globally during the Precambrian Era. The students examine and describe each of the samples visually using terminology regarding their rock texture and associated features. The students then describe or suggest what the rock properties suggest about the process of formation of the rock and the depositional or geologic environment in which the rock formed. Students then collate the data given the relative ages of the rocks and hypothesize how or where these rock units and features could possibly have formed in this association.
Determining whether students have met the goals
Students must fully complete the attached worksheet and come up with a plausible explanation for 3 or more rock units or processes. They must also come up with some possible hypothesis about why or where these rocks could be found together. More information about assessment tools and techniques.
Download teaching materials and tips
I utilize a figure showing the Greenstone Belt sequence from the Wicander & Monroe text Historical Geology: Evolution of Earth & Life through time. It shows the relative ages and cross-cutting relationships to support the chart.