Class Copy – Do Not Write On This Paper. Return this sheet at the end of class.
Constructing a Geologic Time Scale
Problem: What can be interpreted from a time line that plots, to scale, a series of dates from the Earth’s
past?
Materials: Meter stick, 5 meters of adding machine tape, pencil, markers, picture page, tape
Procedure: You will be working in a small group to produce ONE timeline for your group.
1. Measure out 5 meters of adding machine tape.
2. Mark a vertical line at the left edge of the tape and label it 0. This will represent your starting point at
PRESENT day. Label this line “The Present”.
3. Starting at 0 each time, measure 1 meter – mark a line and label this “1 billion years ago”, measure 2
meters from the present - mark a line and label this “2 billion years ago”, continue marking each meter
the fifth line should be labeled “5 billion years ago.
4. Each millimeter represents one million years. MYA = million years ago. Each meter is 1 billion years.
5. Draw a GREEN horizontal line down the middle of the time line from 0 to 65 mm. Label this line the
Cenozoic Era.
0
P
r
e
s
e
n
t
65 mya
Cenozoic Era
6. Using a BLUE marker continue the horizontal line from 65 mm to 225 mm. Label this line the Mesozoic
Era.
7. Using a YELLOW marker continue the horizontal line from 225 mm to 570 mm. Label this line the
Paleozoic Era.
8. Using a RED marker continue the horizontal line from 570 to 4600 mm. Label this line the Precambrian
Era.
9. Label the following Periods on your time line.
Cambrian 570-505 mya
Triassic 225-208 mya
Ordivician 505-438 mya
Jurassic 208- 144 mya
Silurian 438-408 mya
Cretaceous 144-65 mya
Devonian 408-360 mya
Carboniferous 360-286 mya
Permian 286-225 mya
Tertiary 65- 2 mya
Quaternary 2- 0 mya
10. Cut out the pictures of plant and animal life, measure the distance and tape or glue each picture to its
correct place in the time line. Remember always measure from the present line. Some pictures may overlap –
you may place them so they extend above and below the adding machine tape,
Class Copy – Do Not Write On This Paper. Return this sheet at the end of class.
11. Label the events listed below on your time line.
Event
Last Ice Age Ends
Man appears in Colorado
First human ancestors
Florrisant Fossil Beds formed in eruption of 39 Mile Range
Laramide Orogeny (Modern Rockies Formed)
Shallow seas cover Colorado
Ancestral Rocky Mountains Completely Eroded
First photosynthetic bacteria in the oceans
Ancestral Rocky Mountains Form
Shallow seas cover Colorado
Oxygen reaches 20% (present levels)
Pikes Peak Granite intrudes
Rifting and faulting and erosion in Colorado
Oxygen begins to build up in atmosphere
Oldest Earth Rocks
Chicxulub asteroid impact
Earth layers now distinct
Origin of the Earth
Time before present
10,000 years
200,000 years
4.5 million years
35 million years
50-72 million years
85 million years
225 million years
2,700 million (2.7 billion) years
300 -248 million years
510 - 300 million years
380 million years
1,000 million (1 billion) years
1,450 – 600 million years
2,500 million (2.5 billion) years
3,800 million (3.8 billion) years
65 million years
4,400 million (4.4 billion) years
4,600 million (4.6 billion) years
12. For extra credit/honors you may label the Epochs of the Tertiary Period.
Discussion Questions:
Each person will answer the following in their own notebook using complete sentences.
1. During which Era was the surface of the Earth melting cooling and re-melting?
2. During which Era were the dinosaurs the dominant organism?
3. During which Era was there a sudden increase in the invertebrates (animals without back bones) and fish?
4. During which Era did mammals (animals with fur/hair) become dominant?
5. Which lived on the Earth for a longer time, dinosaurs or mammals?
6. List the Eras in order of greatest length of time to shortest length of time.
7. During which Era did oxygen begin to build up in the atmosphere?
8. What organisms were probably responsible for the build up of oxygen?
9. How many years does 1 cm represent on this time line?
10. Did you have any difficulty plotting any of the events on the list? If so, WHY?
Extra Credit/Honors
11. How long would this time line have to be if we wanted to show more recent events?
a. Calculate the length of the time line if we were to use a scale of 1 mm equals 10 years for a 5 billion year
time line.
b. Using a state road map how far west from here would your new time line have stretched?
12. Geologic events affect organisms and organisms can in turn affect the Earth. Write a paragraph to explain
and provide evidence for this claim.