Geologic Time Scale
Time span of Earth’s past is so great that geologists use the geologic time scale to show Earth’s
history. The geologic time scale is a record of the geologic events and the evolution of life
forms.
1. Fill in the data table to show the number of millions of years each Era lasted:
**Note: Round percent to nearest .5% to make sure they add up to 100%.
The Divisions of Geologic
Time
The age of the Earth
a. Cenozoic Era
b. Mesozoic Era
c. Paleozoic Era
d. Precambrian Time
Percent
Millions of years ago
100%
1.5%
4%
6.5%
88%
4,600 ma
2. Create a pie chart to show the percentage of time each Era of geologic time represents in
the Geologic Time Scale: Indicate legends by coloring the given percentage of Division of
Geologic Time: a. yellow; b. pink; c. green; d. blue
3. Write the appropriate periods of the following important events:
IMPORTANT EVENTS & TIME
PERIODS
a. single-celled organisms: 3,500 million years ago
b. Trilobites: 500 million years ago
c. Early land plants: 430 million years ago
d. Reptiles: 280 m.y.a.
e. Fish: 395 m.y.a.
f. Whales: 20 m.y.a.
g. Dinosaurs: 225-65 m.y.a.
h. Mammals: 65 m.y.a.
i. Humans: 2.5 m.y.a.
j. Birds: 120 m.y.a.
k. Pangaea starts to separate: 225 m.y.a.
4. What do you notice about the complexity of the fossils as we move through the Geologic
Time Scale from the Precambrian Times to Quaternary Period? What can you conclude from
your observation?