The Passage of Time

Background

The Geologic Time Scale is a timeline representing the life of the Earth. It encompasses literally billions of years. Although most of us understand that time is measured in linear sequence, comprehending events that took millions of years to happen or that took place millions of years in the past is difficult. In the following activity, students will try three different exercises to help them more clearly understand the time scale with which the Earth measures its "life."

Resources/Materials/Supplies

Video Programs 1 & 2

Graph paper

Notebook paper

Pencils or thin magic markers

Internet access

Teacher Directed Activity 1

Review the video segments (those that discuss the tectonic events that created the Aleutian Range of today). Discuss:

• What geologic events were involved in creating the Mt. Katmai and surrounding mountains?
• How long did this sequence of events take, beginning with the sea floor spreading that created the Pacific Island Arc, to glaciers that stopped the chemical processes creating the copper ore? How long did it take to move from the first glacier to now?
• What other objects or concepts can you name that might help you imagine such numbers as 300 million years? For example, how do the number of years from the creation of the Pacific Island Arc to today compare to the number of miles to the moon? To the first star? To the number of dollars in the national debt?

Distribute the graph paper and pencils/markers. Direct students to fold the paper lengthwise into 3 equal columns and title, Personal Time Scale; title the left column, Intervals; the middle column Millions of Years Ago; the right column Events.

• Have them list on notebook paper at least 10-20 events in their lives, beginning with their birth and ending with an event that occurred in the past 24 hours.
• Invite students to work on this together so that they can prod each other's memories for events.
• Have them arrange their lists in sequence from most recent to least recent.
• Instruct students to inscribe the events of their lives in order from top to bottom in the right hand column, beginning with the most recent event, ending with birth. Explain that they have created a sequential timeline exactly like that created by scientists to chronicle the events of Earth's "life."
• Using their Personal Time Scales, they could describe their growing up and may be able to identify prerequisites to certain events. For example, "I learned to ride my bike with training wheels before I learned to ride without them."
• In the middle column, have students write the number of years from the present that each event occurred. This is the Numerical Time Column.
• Designate the present as zero in the column.
• Number events according to number of years back from the time it occurred.
• The last number in the column would be the student's age.
• Using these 2 sets of information together, students could begin to determine the number of years it took them to learn a new skill or at what (class average) age the class learned to walk or recite the alphabet.
• Scientists divide Earth's timeline into specific intervals, such as Jurassic or Precambrian. Use the left-hand column to show students larger, descriptive intervals for their own lives.
• Using the left-hand column, have students divide their timelines into the following intervals: Preschoolian, Gradeschoolian, Midschoolian.
• Can they think of natural divisions within these larger groupings? For example, could the Preschoolian age be further divided into Crawlian and Walkian? Brainstorm a number of such possible divisions with students and then have them complete their Personal Time Scales.
• Color code intervals created in the first column across the chart to show what events and numerical designations belong in each major interval division.

Distribute copies of the Geologic Time Scale from one of the attached Hot Links and invite students to compare them to their Personal Time Scales.

Have students use the geologic time scales to describe events in Earth's "life" in the same way they described events in their own lives.

• What happened in the Precambrian interval of Earth's life? How many years ago?
• At what point in the Geologic Time Scale did the Aleutian Range form?
• In what time interval did the first glacier bring a halt to the chemical reaction that formed the copper ore?

Teacher Directed Activity 2

You need a large measured space ó football field, basketball court. Students must be able to use the following ratio equation to solve for an unknown. Note: In the equation, "metaphor" represents the large space you've chosen to represent Geologic Time Scale.

Known Age of Past Event (Years Before Present) Time Scale Metaphor (Distance Unknown) X

----------------------------------------------- = -----------------------------------------

Known Age of the Earth (Years Before Present) Maximum Measurement of Metaphor

Review the video with students to discover the geologic time of the following events:

• Creation of the Pacific Island Arc
• Collision of the Yucatan Terrain with the North American continent
• Beginning of the Ice Age
• Novarupta eruption.

Have students add these events to the Geologic Time Scale used in the first activity.

Discuss the ratio equation above. Have students copy the formula on a sheet of scratch paper, share the maximum measurement of the space you are using for the Geologic Time Scale metaphor, and add the known information into the formula.

Take students to the space. Designate one end of the space as Present and the other as the beginning of Earth's history.

• Divide students into 5 groups. Assign one of the above events to each group.
• Have groups calculate in yards (or feet depending upon the metaphor) the distance the point on the scale at which their assigned event took place.

Groups should move the appropriate distance from the starting point on the space.

Once in place, in order, groups can name their event and tell when it took place.

Gather students. Start a discussion comparing time from a geologic point of view and time from a human point of view. Do students agree or disagree that human beings are every bit as catastrophic to the Earth's development as moving crustal plates or ice ages? Why or why not?

Student Directed Activity

Have students follow the directions from their pages to create an illustration of the geologic time scale using a metaphor of their own choosing. Be sure they indicate the events that resulted in the creation of the Valley of 10,000 smokes.

Management Tips and Hints

Rather than expect individuals to complete the metaphor assignment as homework give groups class time to work together on the assignment. Invite one group to create a display for the class or the school to teach observers about geologic time.