Name ____________________________________________
Understanding Geologic Time
Sometimes geologists want to know about an event that occurred before
humans were around to record it. They have evidence of when the event
occurred by looking at rocks, which contain fossils and other information. To
keep all of the events in order, geologists have created the geologic time scale.
The geologic time scale is divided into 3 eons, and each eon is subdivided into
eras. Eras are then subdivided into periods, which are further separated into
epochs. This may sound confusing, but looking at a real geologic time scale and
completing this activity will help.
Instructions:
Use the Event Log on the next page to fill in the Geologic Time Field and answer the Investigation questions.
1. Calculate the distance each event should be from the beginning. Do this by taking the “Approximate
Age” and dividing it by 5 billion (5,000,000,000) and multiplying by 100. Record that number in the
“Distance (yds)” column. This number represents where you should place that event on the Geologic
Time Field.
Equation
(“Approximate Age” ÷ 5,000,000,000) X 100 = Distance (yds)
2. On the back of the Event Log write all the events in order.
3. Place all the events on the Geologic Time Field in order by either writing the event name using a line or
using the numbers from Number 2. Use both the top and bottom of the field so that things don’t get
too cluttered. Each yard in this field represents 50 million years.
As you place events, pay close attention to which end is which!!
4. Pick a color for each Eon and shade in (lightly) the space for that eon on the field (3 colors total).
Investigation:
1. What event is exactly in the middle of the football field?
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2. Find where your birthdate would be on the football field.
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3. What would the average human lifespan be on the football field? (Assume 80 years)
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4. In what Era did the following things first appear?
a. Fish
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b. Mammals
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c. Reptiles
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d. Amphibians
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e. Plants
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5. Looking at the geologic time scale. Why do you think the Phanerozoic Eon has many more divisions and
dates associated with it than the Archean Eon?
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6. How many years does the first 10 yards represent? (if you read the instructions carefully you will be
able to do this)
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7. What events take place within the first 10 yards of the football field? (0 – 10)
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GEOLOGIC EVENT
Approximate Age
First known fish
510 million years ago
Phanerozoic Eon begins
570 million years ago
Paleozoic Era begins
570 million years ago
Earliest humans
2 million years ago
Formation of the Earth
4.6 billion years ago
First known mammal
200 million years ago
Proterozoic Eon begins
2.5 billion years ago
First single-celled organisms
1.2 billion years ago
Aztec Empire begins
587 years ago
Oldest rock
3.8 billion years ago
Extinction of the dinosaurs
65 million years ago
First known plant
498 million years ago
First known reptile
325 million years ago
First multi-celled organism
700 million years ago
First known amphibian
375 million years ago
First known bird
160 million years ago
Mesozoic Era begins
240 million years ago
Cenozoic Era begins
66 million years ago
Archean Eon begins
3.8 billion years ago
Triassic Period begins
240 million years ago
Jurassic Period begins
205 million years ago
Distance (yds)
1. _Formation of the Earth_______________________________
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_Aztec Empire begins_______________________________