Metaphor for the geologic time scale

Cara Thompson
Department of Geosciences, Stony Brook University


Students choose an object or concept that they are familiar with (e.g., football field, pint of beer, etc) and calculate the cumulative amount of that object or concept that represents intervals of geologic time. This assignment is relatively simple and common, but I find that it is fun for students and helps them grasp when key events in Earth's history occurred.

Used this activity? Share your experiences and modifications



I use this assignment in introductory historical geology class.

Skills and concepts that students must have mastered

Students must be able to perform simple calculations in order to scale their metaphor correctly.

How the activity is situated in the course

I have students complete the assignment early in the semester so they can refer back to it as we walk through Earth's history during the semester.


Content/concepts goals for this activity

This assignment is designed to help students understand the vastness of geologic time and when key events in Earth's history occurred relative to each other. Since we spend relatively little classroom time on the Hadean, Archean, and Proterozoic, which represents most of geologic history, I find that a visualization of the time scale helps students appreciate these intervals relative to the Phanerozoic.

Higher order thinking skills goals for this activity

It is my hope that this assignment helps students think about biospheric, oceanographic, and geologic changes on long time scales, rather than human time scales and they are able to translate these skills to their understanding of how the Earth responds to events like changing atmospheric CO2.

Other skills goals for this activity

I encourage students to be as creative as possible in their metaphor.

Description of the activity/assignment

This assignment serves as an introduction to the geologic time scale and to help students visualize the long time intervals between major events in Earth's history. The assignment encourages students to choose a metaphor for geologic time, research major events throughout Earth' history, and calculate how much (cumulative) of their metaphor each time interval represents.

Determining whether students have met the goals

Students are tested on when major events in Earth's history occurred. I find that students who embraced the geologic time metaphor assignment have a better idea of when these events occurred relative to each other and are less likely to confuse Ma and Ga when citing a time interval.

More information about assessment tools and techniques.

Teaching materials and tips

Other Materials