Name
Date
Class
The Geologic Time Scale
Inquiry Warm-Up, This Is Your Life!
In the Inquiry Warm-Up, you investigated how to make a model of a geologic time scale.
Using what you learned from that activity, answer the questions below.
1. OBSERVE How many periods make up your time line? Which is the
longest period, and which is the shortest period? Explain.
2. INTERPRET DATA Which period contains most of the important events
in your life?
3. DRAW CONCLUSIONS What can you conclude about the relationship
between the length of a period and the importance of the events in
that period?
4. GRAPH In the space below, sketch a timeline for a person you know
who is much older than you are. How would you construct a timeline
representing this person’s life? How would you choose to divide this
timeline into parts? Note the ways in which this timeline is both
similar to and different from your own timeline.
123A
Name
Date
The Geologic Time Scale
What Is the Geologic Time Scale?
1a. DEFINE The geologic time scale is a record of
and
.
b. SEQUENCE Number the following periods in order from earliest to
latest.
Neogene
Quaternary
Cretaceous
Jurassic
Triassic
c. DRAW CONCLUSIONS Refer to My Planet Diary and Figure 2. During
which period did modern humans arise?
I get it! Now I know that geologic time
I need extra help with
123B
Class
Name
Date
Class
The Geologic Time Scale
On a separate sheet of paper, summarize how scientists classify geologic time.
123C
Name
Date
Class
The Geologic Time Scale
Understanding Main Ideas
Put the following items in order from oldest (D) to most recent (A) by writing a letter in
the blank beside each one.
1.
Mesozoic Era
2.
Precambrian Time
3.
Cenozoic Era
4.
Paleozoic Era
Answer the following questions on a separate sheet of paper.
5. Why is the geologic time scale used to show Earth’s history?
6. How would you rewrite the following sentence to make it true?
Geologists subdivide periods into eras.
7. What methods did geologists use when they first developed the
geologic time scale?
8. How did geologists decide where one division of the geologic time
scale ends and the next begins?
Building Vocabulary
Match each term with its definition by writing the letter of the correct term in the right
column on the line beside the definition in the left column.
9.
10.
11.
a unit of geologic time that subdivides eras
A. period
a long unit of time used to divide the time between
Precambrian Time and the present
B. geologic time scale
a record of the geologic events and the evolution of life
forms as shown in the fossil record
C. era
123D
Name
Date
Class
The Geologic Time Scale
The figure below shows how old the layers of the Grand Canyon are. Answer the
questions that follow on a separate sheet of paper.
A Young Canyon Made of Old Layers
As the Colorado River cut down through Earth’s crust to form the Grand Canyon, it exposed layer after
layer of sedimentary rock.
1. Did any of the rock in this part of the Grand Canyon form before the
Paleozoic Era began? Explain.
2. During which period did the Redwall limestone form?
3. During which period did the Bright Angel shale form?
4. During which period did the Coconino sandstone form?
5. Did any of the rock that forms the Grand Canyon form during the
Mesozoic Era? Explain.
6. What periods of the Paleozoic Era are not represented by rock of the
Grand Canyon? How might you account for such gaps?
123E
Name
Date
Class
The Geologic Time Scale
If the statement is true, write true. If the statement is false, change the underlined word
or words to make the statement true.
1.
The geologic time scale is a record of the geologic events and
the evolution of life forms as shown in the fossil record.
2.
The first step in developing the geologic time scale was
studying rock layers and index fossils worldwide.
3.
Scientists divided the time between Precambrian Time and the
present into four units of time, or eras.
4.
Periods are subdivided into units of geologic time called eras.
Fill in the blank to complete each statement.
5. Because the time span of Earth’s past is so great, geologists use the
time scale to show Earth’s history.
6. Scientists chose where units of geologic time began and ended based on major
changes in
at certain times.
7. The long span of time that begins geologic time is called
.
8. Geologists divided the time between Precambrian Time and the present into three
long units of time called
.
9. The Triassic Period, the Jurassic Period, and the Cretaceous Period occurred in the
Era.
10.
for many of the geologic periods come from places around the
world where geologists first described the rocks and fossils of that period.
123F
The Geologic Time Scale
Answer Key
8. The divisions of the geologic time scale depend
on events in the history of life on Earth.
1. Answers will vary. Students may choose to use
the three periods suggested in the activity.
Periods will vary according to students’ choices
about how to divide their timelines into parts.
9. A
10. C
11. B
2. Answers will vary.
3. Answers will vary. Students may indicate that
the most important events do not necessarily
appear in the longest period of the timeline.
1. Yes. The bottom slanted rock layers formed
in Precambrian Time, which was before the
Paleozoic Era.
4. Students’ timelines will vary. Some students
may construct this timeline with the same
number of periods, each period spanning a
greater number of years than the periods in
their own timelines. Other students may divide
the older person’s timeline into a greater
number of periods.
2. Carboniferous Period
3. Cambrian Period
4. Permian Period
5. No. The rock layers end with the Permian
Period, which is before the Mesozoic Era began.
6. Neither the Ordovician nor the Silurian periods
Scientists divided geologic time into parts, based
on times in Earth’s history when there were major
changes in life forms. The geologic time scale is
divided into Precambrian time and three eras.
These three eras contain between three and six
periods of time.
are represented by rock layers. It could be
that no sediment was deposited during those
periods or that layers formed but were later
eroded away.
1. true
2. true
1. C
3. false; three
4. false; Eras, periods
2. A
5. geologic
6. life forms
3. D
7. Precambrian Time
8. eras
4. B
9. Mesozoic
5. Geologists use the geologic time scale to
show Earth’s history because the time span of
Earth’s past is so great.
6. Geologists subdivide eras into periods.
7. They studied rock layers and index fossils
worldwide. With that information, they placed
Earth’s rock layers in order by relative age.
123G
10. Names
123H