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# Geologic Time Scale Model: Earth's History on a Football Field (page 2)

By Pam Walker| Elaine Wood
John Wiley & Sons, Inc.

Earth is about 4.6 billion years old. In its infancy, the planet was made of hot molten rock that slowly cooled. When Earth was about 3.5 billion years old, life began to appear in the form of simple cells. Billions of years are difficult to visualize. To put that time frame of Earth's history into periods that we can comprehend, we can make a scaled-down model. In this activity you will fit the entire history of the Earth on a football field.

### Materials

Pencil; Ruler; Paper

### Activity

1. Draw an imaginary football field on your paper. The length of a football field from one goal line to the other is 100 yards. Turn the paper horizontally and draw two goal lines at opposite ends of the paper. Now make equal spaces in between the goal lines so you have lines indicating 10, 20, 30, 40, 50, 60, 70, 80, and 90 yards. The first goal line is 0 and the last goal line represents 100 yards.
2. On the 0 yard line, write "today." On the opposite goal line, write "origin of the Earth."
3. To position some of the important events in the history of the Earth on the football field, use the following formula and solve for X. In each calculation, X represents the location of the event on the football field.
4. Use the formula above to calculate three important Earth events on the football field. Once you solve for X, write each event in the correct place on the football field. Following are the three events:
• Oldest evidence of life: 3,800,000,000 years ago
• Oldest fish fossils: 510,000,000 years ago
• Homo sapiens (humans) appear in fossil record: 100,000 years ago

### Follow-Up Questions

1. What values did you get for the three events you calculated?
2. How far away in yards is the appearance of humans from the first life form?

1. Oldest evidence of life: 3,800,000,000 years ago (82 yards)
2. Oldest fish fossils: 510,000,000 years ago (11 yards)
3. Homo sapiens appear in fossil record: 100,000 years ago—(0.002 yards)
4. Just over 80 yards

### Extension

Do some research to find other important events in Earth's history. Position the events on the appropriate yard lines on your imaginary football field.

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