# Relative Dating on Earth and Mars

Sara Harris
,
University of British Columbia
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#### Summary

Students apply principles of relative dating to a cross-section, then to the surface of Mars.

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## Context

#### Audience

I use this in an introductory-level course for non-science majors, who are in the course to fulfill a general education requirement.

#### Skills and concepts that students must have mastered

Students should have read about principles of relative dating and the principle of uniformitarianism. The activity asks them to apply the principles, so it's OK if they haven't yet mastered them.

#### How the activity is situated in the course

This is a short (~10 minute) exercise in class that supports learning about how geologists decipher histories from rocks.

## Goals

#### Content/concepts goals for this activity

Application of principles of relative dating. Extension activity combines relative and absolute dating.

#### Higher order thinking skills goals for this activity

Make logical inferences based on observations.

#### Other skills goals for this activity

Working in groups; explaining principles to other students.

## Description of the activity/assignment

This activity asks students to interpret (1) a geologic cross-section, then (2) the surface of another planet (Mars) in order to construct a logical sequence of events that explain how it came to look the way it does. Students need to use principles of relative dating, such as superposition, cross-cutting relationships, inclusions, original horizontality, or original continuity. An extension activity adds a few absolute dates and a couple of fossils to the original cross section and asks students to bracket the possible range of ages for an undated feature of the cross-section.

## Determining whether students have met the goals

On a quiz, I ask students questions about individual principles (e.g. which layer is youngest?). On an exam, I ask students to interpret a sequence of events for a different cross section than the one they saw in the activity. I survey students about the in-class activities and ask which they thought were particularly useful/not useful. This one is often mentioned as an activity students remember, usually in a positive light.