Crater Counting Lab exercise
Kevin F. Mullins
Coconino Community College / Science Dept.
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This lab is designed to teach students how we can estimate the age of other planetary surfaces by counting and size-binning impact craters. It also illustrates some examples of how erosional or deopositional processes can modify or resurface crustal areas essentially restting the clock of the cratering process.
This class is an introductory level, GenEd lab science course. Because of our proximity to NAU, Lowell Observatory and the Astrogeology Group at the USGS I get a significant proportion of Earth Science majors taking the class. We begin the class with a brief intro to the Universe and eventually after discussing the Big Bang Theory we get into the concepts of time and relativity. This lab serves two purposes in the class: 1) to understand the most prevelent geologic process in the SS and 2) to assist in an understanding of time on a planetary scale.
Skills and concepts that students must have mastered
Some basic math is involved along with a need for carefully collecting data to minimize errors in the results. The concepts of accretion and the impact process and its resulting features are needed. We study asteroids and comets (making one in lab is always fun), the cratering process and visit Meteor Crater on an extended field trip. Carolyn Shoemaker usually guest lectures before we dive into the lab about her exoeriences in comet hunting.
How the activity is situated in the course
It is just one of 8 lab exercises I provide for the students during the course of the semester. The next lab entails undestanding and recognizing Earth Analogs as a method of identifying landforms and processes on other planetary surfaces.
Content/concepts goals for this activity
Age dating of planetary surfaces based on the number and size distribution of impact features. Crater counting uses the Moon's surface as a control data base to extrapolate age estimates for other planetary surfaces.
Students also get fundamental experience in recognizing how other geologic and atmospheric processes modify and resurface planetary crusts and how those processes affect our interpretation of plantary surficial evolution.
Higher order thinking skills goals for this activity
The students must first correctly identify and compile their data from two images sets. Minimizing errors through miscounting and misidentifcation is stressed. Calculations are mathematically simple but plotting the data, estimating the best fit line and determining both an age and its estimated accuracy is necessary to fulfill the assignment.
Other skills goals for this activity
I do allow the studnets to work in groups but each must make their own conclusions and show their work.
Description of the activity/assignment
This lab focuses on the identification of impact features, and how they can used to estimate the age of planetary surfaces. Key comcepts include understanding how the crater process has changed over geologic time; how those changes manifest themselves in the surficial record of planetary landforms; how other planetary processes modify surficial landforms; how the conditions of the Solar System have changed over time.
Determining whether students have met the goals
Errors due to inexperience and resolution limitations of the imagery used in the lab make the biggest impact on how well students accomplish this lab. I do expect their numbers to approach the the ones I compiled on doing the exercise myself. Correct calculations regardless of data collection errors are required and accurate plots and age dates with quantitative error estimates are expected.
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