Geologic Time Measurement – Grade Ten
Ohio Standards
Connection:
Earth and Space
Sciences
Benchmark C
Explain the 4.5 billionyear-history of the Earth
and the 4 billion-yearhistory of life on Earth
based on observable
scientific evidence in the
geologic record.
Indicator 3
Explain how geologic
time can be estimated by
multiple methods (e.g.,
rock sequences, fossil
correlation and
radiometric dating).
Related Standard
Life Sciences
Benchmark I
Explain how natural
selection and other
evolutionary
mechanisms account for
the unity and diversity of
past and present life
forms.
Indicator 25
Explain that life on Earth
is thought to have begun
as simple, one celled
organisms approximately
4 billion years ago.
During most of the
history of Earth only
single celled
microorganisms existed,
but once cells with
nuclei developed about a
billion years ago,
increasingly complex
multicellular organisms
evolved.
Lesson Summary:
This lesson allows students to gain an understanding of
various methods (e.g., rock sequences, fossil correlation,
radiometric dating) used by scientists to estimate geologic
time. Students will read in the content area, use note-taking
strategies and analyze the advantages and disadvantages of
methods currently used to determine geologic time.
Estimated Duration: Three hours
Commentary:
This lesson helps students learn about methods used to
estimate geologic time. Students will have opportunities to
learn about and apply their knowledge using an approach,
which includes engagement, exploration, explanation and
expansion. Learning strategies include a two-column notetaking exercise, which helps students organize their notes
around major content topics.
This lesson was pilot tested by teachers across the state of
Ohio. Some of the teacher comments about this lesson were:
“This is a good lesson. I wouldn’t change anything.”
“Students enjoyed the topic, and would have liked to
spend more time with it.”
Pre-Assessment:
 Print questions found in Attachment A, PreAssessment, and distribute to students.
 Direct students to answer the questions to the best of
their abilities.
Scoring Guidelines:
See Attachment B, Pre-Assessment Answers, to assess
student responses to the pre-assessment.
Post-Assessment:
 Print questions found in Attachment C, PostAssessment, and distribute to students.
 Direct students to answer the questions provided.
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Geologic Time Measurement – Grade Ten
Scoring Guidelines:
See Attachment D, Post-Assessment Answers, to assess students’ responses.
Instructional Procedures:
Engagement Activity: Observing the Past
1. Have students participate in any one of the following activities to help pique student
interest:
 Have fossils or models of prehistoric life available for students to observe.
 Have pictures of prehistoric life for students to observe.
 Show a video clip of fossils, dinosaurs, prehistoric man, or layering of rocks such as
those found in the Grand Canyon.
 As an analogy to sedimentary layers, fill a deep, clear bowl with layers of different
colors of gelatin. Have fruit and/or marshmallows in some of the layers and not
others. One color layer could even be repeated. An overhead transparency or colored
drawing could represent the same concept.
2. After the students have had three to five minutes to participate in any of these activities,
move onto the Exploration Activity.
Exploration Activity: What Does It Mean?
3. Prepare thinking cubes using printouts of the figure in Attachment E. Prepare enough so
that each pair of students in the class will have one.
4. Inform students that they will keep a science journal or a science notebook. Entries
should be kept in an organized, sequential manner.
5. Inform students that the objective for the lesson is to respond to prompts that will help
them expand their thinking about how geologic time can be estimated by multiple
methods.
6. Have the students work with partners. Give each pair a thinking cube.
7. Instruct students to roll the cube and respond in writing in their journals to the prompt
about what they observed in the engagement activity (e.g. fossils, pictures). Students
should write for a short period of time. Inform them when the time is up.
8. Have students roll the cube again and respond to the second prompt. If the cube lands on
the same prompt a second time, roll the cube until it lands on a different prompt.
9. Have the students roll the cube a third time.
10. After responding to three prompts, have the students share their responses with their
partners.
11. Have students form groups of four and share their answers to the prompts.
12. Lead the class in a discussion of ideas they have generated/predicted/hypothesized about
what they observed in the engagement activity. These ideas could be put on poster paper
and left posted for the students to see throughout the study of geologic time.
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Geologic Time Measurement – Grade Ten
Explanation Activity: Methods for Establishing Geologic Time
13. Show students how to employ a two-column note-taking system. Use Attachment F, TwoColumn Note-Taking Instructions, to guide the students. See Attachment G for an
example of two-column notes.
14. Use a lecture format to cover the major concepts of how geologic time is established or
have the students read textbooks on this topic. Make sure that at least the topics of rock
sequences, fossil correlation and radiometric dating are covered.
15. After the students have taken notes, have a follow-up class discussion to make sure the
students have all the major concepts covered.
Instructional Tip:
Develop a few problems that require the students to practice determining the age of
something using the radiometric method. You may also want students to go back to their
journal entries from the thinking cube activity and highlight the ideas that support current
knowledge of methods of determining geologic time.
16. Perform a formative assessment of student learning. In their notebooks, have students do
a three minute free-write exercise titled, “What I know about fossils in relation to
geologic time.”
Scoring Guidelines:
Students should indicate that index fossils are the remains of organisms which existed on
earth for a short period of time, and that the time frame has been well documented by
scientists. Students should also indicate that when an index fossil shows up in a rock sample,
it makes it easy to place a date on that rock sample because the time frame when the index
fossil lived has been established.
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Geologic Time Measurement – Grade Ten
Expansion Activity: Determining Geologic Time Poster
17. Have the students make a poster that summarizes rock sequencing, fossil correlation and
radiometric dating for determining geologic time. Here is an example of the information
the teacher might want to have students include on their posters:
METHOD
ROCK
SEQUENCING
FOSSIL
CORRELATION
RADIOMETIC
DATING
Outline of basic
principles of the
method.
Advantages of
using this
method.
Disadvantages of
using this
method.
Graphic that
explains method.
This format could be used for a poster, or another student-developed design.
Differentiated Instructional Support:
Instruction is differentiated according to learner needs, to help all learners either meet the
intent of the specified indicator(s) or, if the indicator is already met, to advance beyond the
specified indicator(s).
 The teacher might want to use Attachment G, Two-column Note-taking Example as a
template with just key ideas and allow the students to fill in the right-hand column. The
template could be used with all students or with only those students with learning
disabilities or who are academically challenged.
 Encourage visual learners to make small drawings in the left column of the two-column
notes for key ideas or terms.
 Pair students to edit each other’s two-column notes.
 Have students who are struggling with the vocabulary and concepts make and use
flash cards.
 Students who are working beyond the standard may develop an independent study
proposal using the Extension Activity.
Extensions:
 Ohio Fossils: On a map of Ohio, have students mark the locations of where there have
been major fossil finds.
 Students may design a ledger in table format that names the types of fossil that were
found at each of the sites indicated on the map. The table should include the name of the
site, the name of the fossil, the time frame during which the organism lived and indicate
if this fossil is used as an index fossil.
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Geologic Time Measurement – Grade Ten
Site
Name of
Organism
Example of what the table might look like:
Type of Organism Time Frame
Used as an
(Reptile, Mammal, Organism
INDEX
etc.
Lived
Fossil (Yes
or No)
Instructional Tip:
Information about Ohio fossils can be found at the Ohio Geological Survey's Web page.
Additional resources may be found at the Web site for the Ohio Resource Center.



Take students on a real or virtual field trip to a natural history museum.
Construct a concept map about fossils, including such key terms as trace fossils, index
fossils, molds, casts, imprints, sedimentary rocks, amber and tar pits.
Collect and identify fossils that occur in your local area.
Homework Options and Home Connections:
 Take a family trip to a museum to search for information about geologic stratigraphy and
fossils.
Interdisciplinary Connections:
English Language Arts: This lesson engages students in two-column note-taking, and
summarizing information.
Mathematics: This lesson helps students learn to calculate ages of fossil specimens using
isotope half-life data.
Materials and Resources:
The inclusion of a specific resource in any lesson formulated by the Ohio Department of
Education should not be interpreted as an endorsement of that particular resource, or any of
its contents, by the Ohio Department of Education. The Ohio Department of Education does
not endorse any particular resource. The Web addresses listed are for a given site’s main
page, therefore, it may be necessary to search within that site to find the specific information
required for a given lesson. Please note that information published on the Internet changes
over time, therefore the links provided may no longer contain the specific information related
to a given lesson. Teachers are advised to preview all sites before using them with students.
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Geologic Time Measurement – Grade Ten
For the teacher:
Attachments, materials for engagement activity could include books,
fossils, flavored gelatin, fruit, marshmallows, magazines, photographs and
films.
For the students: Thinking cubes.
Vocabulary:
 fossil
 radiocarbon dating
 index fossil
 absolute age
 relative age
 Carbon-14
 radiometric age
 superposition
 Potassium-40
Technology Connections:
 In the Extension activity, students may use the Ohio Geological Survey's Web page. Go
to www.dnr.state.oh.us, and then navigate to the Geological Survey.
 Additional resources about fossils may be found at the Web site for the Ohio Resource
Center, www.ohiorc.org.
Research Connections:
Marzano, R. et al. Classroom Instruction that Works: Research-Based Strategies for
Increasing Student Achievement. Alexandria: Association for Supervision and Curriculum
Development, 2001.
Summarizing and note taking are two of the most powerful skills to help students
identify and understand the most important aspects of what they are learning.
Identifying similarities and differences enhances students’ understanding of and
ability to use knowledge. This process includes comparing, classifying, creating
metaphors and creating analogies
Nonlinguistic representations or imagery mode helps students think about and recall
knowledge. This includes the following:
 Creating graphic representations (organizers),
 Making physical models,
 Generating mental pictures
 Drawing pictures and pictographs,
 Engaging in kinesthetic activity.
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Geologic Time Measurement – Grade Ten
Cues, questions and advanced organizers help students retrieve what they already
know about a topic. Activating prior knowledge is critical to learning new concepts.
General Tips:
 Two column notes are adapted from the Cornell Note-Taking System. Walter Pauk. How
to Study in College, 2nd ed. New York: Houghton Mifflin Co., 1974
Attachments:
Attachment A, Pre-Assessment
Attachment B, Pre-Assessment Answers
Attachment C, Post-Assessment
Attachment D, Post-Assessment Answers
Attachment E, Thinking Cube
Attachment F, Two-column Note-taking Instructions
Attachment G, Two-column Note-taking Example
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Geologic Time Measurement – Grade Ten
Attachment A
Pre-Assessment
NAME:___________________________
PERIOD:_________
1. You and a friend are exploring along a creek bed and you notice layers of different
colored stone in the stream bank. When you examine the bank more closely, you see
fossils in three of the layers in the stream bank. What conclusions can you make about
the relative ages of the fossils? What conclusions can you make about the layers of rock
2. A scientist is trying to determine the age of some bones. He is able to determine that the
bone has one-fourth the amount of Carbon-14 that is in bones today. The half-life of
Carbon-14 is about 5,700 years. What would be the approximate age of the bone?
3. What is an index fossil and why is it important?
4. Why are fossils found in sedimentary rock?
5. A geologist examines where a river has cut through a mountain. He discovers the
following rock sequence (from the bottom to the top) igneous layer, metamorphic layer,
sedimentary layer, igneous layer, sedimentary layer. What could be an explanation for
this sequence of rocks?
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Geologic Time Measurement – Grade Ten
Attachment B
Pre-Assessment Answers
1. The older fossils would be found in the layer of rock closer to the streambed
(1 point).
The older layer of rock would be closest to the streambed and more recent layer would be
closer to the surface. Age could be determined by the presence of indicator fossils.
(1 point).
2. The bones would be approximately 11, 400 years old (In 5,700 years you would see 1/2
of the Carbon-14 normally present in modern bones, and in another 5,700 years you
would see 1/2 of 1/2, or 1/4, of the Carbon-14 normally present in modern bones.)
(1point)
3. Index fossils are the remains of organisms that only existed on earth for a short period of
time that has been well documented by scientists. (1point)
When an index fossil shows up in a rock sample, it makes it easy to place a date on that
rock sample because the time frame when the index fossil lived has been established.
(1 point)
4. If there is a rapid deposit of sediment after an organism dies, there is a greater chance of
that organism being fossilized. (1 point)
Igneous and metamorphic rocks are too hot to allow for fossil formation. (1 point
extra credit if this information is also present in the student response.)
5. An explanation for this sequence of rocks should include folding, faulting, uplifting,
mountain formation or a volcanic eruption. (1 point for any of these answers.)
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Geologic Time Measurement – Grade Ten
Attachment C
Post-Assessment
NAME:___________________________
PERIOD:__________
1. Explain the principle of “superposition.”
2. What is an index fossil and why is it important?
3. What is relative age?
4. List methods that scientists use to determine that life has been on Earth for four
billion years?
5. You are looking around in the bottom of a quarry and find a pile of rocks with
different fossils in them. There are placoderm fish bones, dinosaur bones,
stromatolites (a cyanobacteria), a species of trilobite and a bone of a woolly
mammoth. Place the fossils in order from the oldest to the most recent.
6. A scientist is trying to determine the age of some bones. He is able to determine that
the bone has one-eighth the amount of Carbon-14 that is in bones today. The half-life
of Carbon-14 is about 5,700 years. What would be the approximate age of the bone?
7. A scientist is trying to date a spear, a bone arrowhead and the remains of an ancient
campfire. Would the scientist use Carbon-14 or Potassium-40 to try to date these
ancient artifacts? Defend your choice.
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Geologic Time Measurement – Grade Ten
Attachment D
Post-Assessment Answers
1. When there are undisturbed layers of rock, the oldest rock will be on the bottom.
(1 point)
2. Index fossils are the remains of organisms that only existed on earth for a short period
of time that has been well documented by scientists. (1point)
When an index fossil shows up in a rock sample, it makes it easy to place a date on
that rock sample because the time frame when the index fossil lived has been
established. (1 point)
3. Relative age is the age of something in comparison to the age of something else.
(1 point)
4. Methods that scientists use to determine that life has been on Earth for four billion
years include;
A. Fossil records
B. Rock sequences
C. Radiometric dating
(Total of 3 points)
5. In order, from the oldest to the most recent, the fossils are;
stromatolites, trilobite, placaderm bones, dinosaur bones, woolly mammoth bone
(2 points for totally correct sequence)
6. The bones would be approximately 17,100 years old. (1 point)
7. Carbon-14 would be most appropriate (1 point). Man has been present on earth for a
relatively short time. Potassium-40 has a very long half-life and would not be very
accurate in dating human artifacts. C-14 has a half-life of 5,700 years and could more
accurately date human artifacts. (1 point)
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Geologic Time Measurement – Grade Ten
Attachment E
Thinking Cube
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Geologic Time Measurement – Grade Ten
Attachment F
Two-column Note-taking Instructions
1. Divide your notebook/journal page into two columns. A vertical line should be drawn
three inches from the left edge of the page.
2. Main ideas, key concepts or key terms should be placed in the left column.
3. Class lecture notes or reading notes should be placed in the right column. Lines should be
skipped between main ideas or concepts to allow room to add to the notes at a later time.
4. Source of notes (class lecture, textbook, journal article) should be indicated at the top of
the page along with any learning objectives for the lesson.
5. After reading or lecture the student should do the following:
 Read through the notes.
 Make any scribbles more legible.
 Fill in any incomplete areas.
 Clarify any areas that are confusing.
 Underline or highlight any key vocabulary words.
 Fill in any key ideas or terms that you might have missed putting in the left column.
 Compare and discuss your notes with a classmate. Fill in any additional information.
6. Recall and recite:
 Cover the right column of your paper
 Look at one key concept at a time and recall the details about that concept as fully as
you can in your own words. Recite your thoughts out loud. Uncover the notes on the
left and check to see if you have remembered the essential ideas.
7. Before each class, take a few minutes to review your notes.
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Geologic Time Measurement – Grade Ten
Rock Sequence
Attachment G
Two-column Note-taking Example
-When rock layers have not been disturbed, the oldest layers are
on the bottom and the youngest rock is on the top.
-The oldest rock layer on the bottom is called the principle of
superposition.
Relative age of rock
-Sequencing of rock tells you which layer is older or younger
than that of another layer but does not tell the actual age of the
rock in years.
-Fossils give clues to age of rocks.
Seismologydisruption of rock
sequence
Must look for evidence of seismologic activity to determine if
the rock layers are being read correctly. Such factors as those
listed below can cause rock layers to be rearranged.
-uplifting
-mountain building
-volcanic eruptions
-rifts
-earthquakes
-ocean floor spreading
Index fossil
-Remains of species that only lived on earth for a short period
of time (examples : species of Trilobites, Ammonites).
- When an index fossil is found in a layer of rock, it then helps
determine the age of the rock.
Absolute age
-It is the age in years of rock, fossil or other material
-It is determined by radioactive decay
Radiometric dating
-Some isotopes of elements are unstable and break down by a
process called radioactive decay.
 Parent isotope undergoes radioactive decay to produce
daughter product
 The time it takes for half of parent isotope to break down
is called the half-life
 Half-life of carbon-14 is 5,730 years
 Half-life of potassium-40 is 1.25 billion years
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