Earth Science Week Classroom Activities
Geologic Time Scale Analogy
Activity Source:
Ritger, S.D. and R.H. Cummins. 1991. Using student-created metaphors to comprehend geologic time. Journal of Geological Education. 9:9-11.
Purpose
To introduce students to the vastness of [geologic time](/content/geological- time-scale) and the concept of scale.
Background
Unraveling time and the Earth’s biologic history are arguably geology’s most important contributions to humanity. Yet it is very difficult for humans to appreciate time beyond that of one or two generations, much less hundreds, thousands, millions and billions of years. Perhaps we can only hope that students catch glimpses of our rich geologic heritage, particularly when most of our teaching is done in a classroom and not in a field setting. This exercise begins to make time more “three dimensional” and most importantly, students gain a better appreciation for geologic time and our Earth’s history.
Instructions
To better understand the concept of geologic time, have students produce a time-scale metaphor to share with the class that is true to scale and reflects some of the important events in the history of the Earth (see list on the following page). Write an essay that: (1) discusses why you chose the metaphor you used; (2) shows your math calculations; and (3) discusses what you learned from this exercise including your perspective of where humans fit in the grand scheme of things. Have fun! Be creative! No metaphor is too silly, as long as your math is correct and your choice has meaning to you.
Example:
The method used to determine a metaphor value true-to-scale will be similar for all metaphors. Units in the metaphor model can be in time, distance, volume, mass, etc. depending upon what type of metaphor you choose to work with. The general equation used to generate numbers in your metaphor which will be true to scale is:
| Known age of past event (years before present) ______________________________ Known age of the Earth (years before present) |
= |
UNKNOWN Time scale metaphor equivalent ___________________________ Maximum measurement in metaphor |
For example, suppose your metaphor uses distance. Remember, the use of time, volume, or mass in your metaphor would be just dandy. Since we are using a distance metaphor as an example here, a football field with a length of 100 yards will do just fine. To find at what distance along the football field, for example, the “first oxygen” yard mark would be, you would set up the ratio shown below:
| Known first oxygen (2.01 x 109 years) ________________________________ Known age of the Earth (4.6 x 109 years ago) |
= |
UNKNOWN (first oxygen on football field) ________________________________ 100 yards (Football Field Length) |
So taking the math one step further gives you:
(2.01 x 109 years)(100 yards) = (X yards)(4.6 x 109 years)
Solving the ratio (for X) will tell you that the “first oxygen” location on the football field would be 43.7 yards away from the goal line of your choice! Determining the location of the other important dates in the history of the Earth is up to you.
Some Important Dates in the History of the Earth
| Years Ago | Event |
|---|---|
| 4,600,000,000 | Origin of the Earth |
| 3,900,000,000 | Oldest Dated Crustal Rocks |
| 3,800,000,000 | Oldest Evidence for Life |
| 2,000,000,000 | First Oxygen Atmosphere/Ozone Layer Forms |
| 900,000,000 | Oldest Metazoan Fossils |
| 510,000,000 | Oldest Fossil Fish |
| 458,000,000 | First Land Plants |
| 375,000,000 | That important first step:Amphibians Evolve |
| 245,000,000 | Huge Mass Extinction at End of Permian Period / Close of the Paleozoic Era |
| 200,000,000 | First Mammals |
| 160,000,000 | First Birds |
| 145,000,000 | Atlantic Ocean first opens |
| 130,000,000 | Angiosperms (Flowering Plants) on the Scene |
| 65,000,000 | Adaptive Radiation of Mammals |
| Dinosaurs Go Extinct | |
| Close of the Mesozoic Era/ Beginning of the Cenozoic Era | |
| 3,400,000 | New discoveries of Australopithecus afarensis (Lucy) fossils from Ethiopia |
| 2,000,000 | Pleistocene Ice Age begins |
| Light from the Andromeda galaxy seen today left Andromeda | |
| 600,000 | Age of Homo erectus fossils from Ethiopia |
| 125,000 | Oldest rocks in the Bahamas |
| 100,000 | Homo sapiens appears in the fossil record |
| 15,000 | Last ice sheet retreats from northern United States |
| 7,000 | Grahams Harbor, San Salvador, Bahamas floods due to rising sea level after ice sheets are reduced to modern day volume |
| 506 | Columbus lands in New World |
| ? | You were born |
Earth Science Week Connections
Discover the Earth Sciences
Discuss the age of the Earth’s crust at different locations (i.e. ocean floor, continents, etc.) Is it older in some places and younger in others? What does this tell you about how the Earth’s crust has changed over the last billion years? Discuss plate tectonics.
Geoscientists
Invite a paleontologist to discuss our geologic history.
Stewardship
The time of human life on Earth is incredibly short when compared to Earth’s vast history, yet during our short existence we have permanently altered our environment. Discuss the implications of the environmental crisis as it exists in the context of Earth history.
Earth Science is all around you
How old are the rocks in your state? Look at geologic maps to examine the history of your area.