Scaling events in geologic time

Learning Objectives

  • To create a timeline of Earth's history
  • To make basic scaling calculations
  • To increase knowledge of large numbers
  • To become familiar with the order and rough timing (or numeric age) of major events in Earth's history
  • To get a sense of the scale of human events compared to geologic events
  • To gain familiarity with the metric system (pending method of implementation, use of metric system or not for measurements)

Standards Addressed

6-8 grade band
Earth and Space Science
                  3.3.7.A6 - CONSTANCY/CHANGE SCALE: Describe geologic time as it relates to earth processes.
                  3.3.7.A3 - Explain and give examples of how physical evidence, such as fossils and surface features of glaciation support theories that the Earth has evolved over geologic time.
Science as Inquiry
3.3.6.A6 – Models/Scales – Describe the scales involved in characterizing Earth and its atmosphere.  Create models of Earth’s common physical features.
                  3.1.8.B6 - Explain the importance of accuracy and precision in making valid measurements.
                  3.1.6.A9 - Develop descriptions, explanations, and models using evidence and understand that these emphasize evidence, have logically consistent arguments, and are based on scientific principles, models, and theories.

Supplies/Materials/Articles Needed

Depending upon which method teachers are having students scale geologic time, teachers need to secure a rope with clothespins, or a roll of toilet paper, etc. The version describe here requires Post-It notes, tape measures, and the attached handout.

Preparation Time Needed

Minimal. Teachers should decide ahead of time which geologic events they want students to focus on, secure those dates and make the calculations to have the solutions handy, and be prepared to answer why those geologic events were selected.

Class Time Required

Depending upon how many calculations the teachers have the students complete (if any) and the math level of the students to determine how much class time is required. If a teacher asks students to make an estimation of when geologic events took place along the length of a string, for example, and then calculate the actual position along the length of a string and reposition their estimates, this could take 30-50 minutes. If a teacher will be doing an entire class demonstration and not having students complete any calculations, this "show and tell" exercise could take 10-15 minutes with supporting lecture on geologic time.

Activity Description

This exercise challenges students to think about the order of and spacing between evolutionary events in geologic time. Teachers may swap out and select their own events that are biologic, tectonic, environmental, etc. I start by having the students work in pairs, and I ask them to place the following alphabetical list of "first occurrences" in geologic time in the correct sequential order: dinosaurs, elephants, fish, humans (modern), insects, mammals, plants, reptiles. Then, students share their determinations in groups of four or five. Next, students are asked to use the length of our classroom as the 4.6 billion years of geologic time and place a labeled Post-It note on the floor at the approximate position of the evolutionary event. I then give students the attached handout with the actual geologic dates and have them calculate (encouraging them to set up a ratio) the distance along the floor that represents the date in geologic time of the event. We then discuss the differences between what they estimated and what they calculated and why their perceptions were different.

There are several variations of activities for scaling geologic time that have been classroom tested and shared through the Science Education Resource Center (SERC). Teachers are encouraged to check out these adaptations, as a scaling exercise on geologic time is extremely useful for students before discussing Earth history.