ALEX Lesson Plan


It's All Absolutely Relative: Creating a Geologic Time Scale

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  This lesson provided by:  
Author:Hannah Bradley
System: Dothan City
School: Carver Magnet School
The event this resource created for:ASTA
  General Lesson Information  
Lesson Plan ID: 35216


It's All Absolutely Relative: Creating a Geologic Time Scale


Students will begin this lesson by ordering the events of their morning using relative and absolute dating techniques. Students will also write a personal definition of the terms absolute age and relative age. Next, students will work with collaborative groups to order events in Earth's geologic history by relative age, then order those same events by absolute age in a scaled model timeline. Lastly, students will use the time-scale model created with their group members to analyze events in Earth's geologic history.

This lesson results from a collaboration between the Alabama State Department of Education and ASTA.

 Associated Standards and Objectives 
Content Standard(s):
SC2015 (2015)
Grade: 9-12
Earth and Space Science
8 ) Develop a time scale model of Earth's biological and geological history to establish relative and absolute age of major events in Earth's history (e.g., radiometric dating, models of geologic cross sections, sedimentary layering, fossilization, early life forms, folding, faulting, igneous intrusions).

NAEP Framework
NAEP Statement::
E12.4: Early methods of determining geologic time, such as the use of index fossils and stratigraphic sequences, allowed for the relative dating of geological events. However, absolute dating was impossible until the discovery that certain radioactive isotopes in rocks have known decay rates, making it possible to determine how many years ago a given rock sample formed.

NAEP Statement::
E12.6: Early Earth was very different from today's planet. Evidence for one-celled forms of life (bacteria) extends back more than 3.5 billion years. The evolution of life caused dramatic changes in the composition of Earth's atmosphere, which did not originally contain molecular oxygen.

NAEP Statement::
E12.7: Earth's current structure has been influenced by both sporadic and gradual events. Changes caused by violent earthquakes and volcanic eruptions can be observed on a human time scale; however, many geological processes, such as the building of mountain chains and shifting of entire continents, take place over hundreds of millions of years.

Unpacked Content
Scientific And Engineering Practices:
Developing and Using Models
Crosscutting Concepts: Systems and System Models
Disciplinary Core Idea: Earth's Systems
Evidence Of Student Attainment:
  • Develop a graphical organizer that arranges the broad geologic eons and epochs of Earth's history according to key fossils and radiometric results.
  • Use geologic principles of superposition, original horizontality and relative dating to order the events involved in creating a given rock sequence.
  • Establish radiometrically the age of a rock sample, given the percent of a parent element remaining and a table of half-life data.
Teacher Vocabulary:
  • fossil
  • fossilization
  • folding
  • faulting
  • igneous intrusions
  • rocks
  • time scale
  • Precambrian Era
  • Paleozoic Era
  • Mesozoic Era
  • Cenozoic Era
  • petrification
  • mold
  • cast
  • Principle of superposition
  • Principle of crosscutting relationships
  • index fossil
  • half-life
  • Knowledge:
    Students know:
    • The early Earth and other objects in the solar system were bombarded by impacts. (combined 2)
    • Erosion and plate tectonics on Earth have destroyed much of the evidence of bombardment by impacts, explaining the scarcity of impact craters on Earth.
    • Earth's plates have moved great distances, collided, and spread apart based on evidence of ancient land and water patterns found in rocks and fossils.
    • The geological time scale interpreted from rock strata provides a way to organize Earth's history.
    • Major historical events include the formation of mountain chains and ocean basins, the evolution and extinction of particular living organisms, volcanic eruptions, periods of massive glaciation, and development of watersheds and rivers through glaciation and water erosion.
    Students are able to:
    • Identify age and composition of Earth's oldest rocks and meteorites as determined by radiometric dating.
    • Use evidence to organize the components of the model including a geographical scale showing the geological and biological history of Earth.
    • Describe relationships in the model between components in the model, such as the age and composition of Earth's oldest rocks as determined by radiometric dating, observations of size and distribution of impact craters on the surface of the Earth, and the activity of plate tectonic processes operating on the Earth, sedimentary layering, fossilization, early life forms, folding, faulting, and igneous intrusions.
    Students understand that:
    • Analyses of rock formations and the fossil record are used to establish relative ages.
    • Radiometric ages of lunar rocks, meteorites and the oldest Earth rocks point to the creation of a solid Earth crust about 4.4 billion years ago.
    • Other planetary surfaces and their patterns of impact cratering can be used to infer that Earth had many impact craters early in history.
    • Processes such as volcanism, plate tectonics, and erosion have reshaped Earth's surface.

    Local/National Standards:


    Primary Learning Objective(s):

    • Students will be able to describe the difference between relative and absolute age.
    • Students will create a time scale model of life forms that have existed in Earth's geologic history. 
    • Students will be able to utilize the information detailed on the time scale model to analyze geologic events in Earth's history.

    Additional Learning Objective(s):

     Preparation Information 

    Total Duration:

    91 to 120 Minutes

    Materials and Resources:

    Student Materials (per student)


    "It's All Absolutely Relative" Handout (see attachments)

    "Geologic Time Scale Model Reflection Questions" Handout (see attachments)

    Student Materials (per group)


    Metric Ruler

    Glue or tape

    "Geologic Events-Life Forms Cards" (see attachments)

    4.6 meters of adding machine tape, toilet paper, or another material cut to the appropriate length 

    "Geologic Events-Life Forms' Absolute Age Cards" (see attachments)

    Teacher Materials

    Geologic Events-Life Forms Absolute Age Cards Teacher Key (see attachments)

    Website for Acceleration Intervention Activities

    "Geologic Time" from the University of California Museum of Paleontology at Berkley

    Technology Resources Needed:

    Student Materials

    Students will need an internet capable device for the review activity listed in the Acceleration and Intervention portions of the lesson


    According to most scientists, the Earth is approximately 4.6 billion years old. Scientists have gathered information about Earth's biologic and geologic past by studying information, such as fossils and radioactive materials, within rock strata. During the first billion years of Earth's geologic history, no life existed on Earth. According to scientists, the first organisms to develop were anaerobic prokaryotes, such as bacteria, then over the next several billion years, life as know it evolved. As this amount of time is very difficult to comprehend, it is helpful to create scaled models to determine the sequence of events in Earth's geologic history.

    Since this lesson serves an introduction to geologic time scales, including relative and absolute age, students do not need to have an understanding of these concepts before beginning the lesson. This lesson will require students to work in collaborative groups to create a scaled model timeline. The teacher may wish to teach the skill of creating a scaled model before beginning this lesson, or the teacher can teach this skill during the lesson by scaffolding students as they calculate the scaled conversions.

    The teacher will need to make copies of the attached handouts for each student/group and prepare the materials needed for the collaborative timeline activity.

    Note: This lesson was adapted using ideas and information from the following websites. The teacher can visit these websites for additional information about the lesson's content:


    Before Strategy/Engage: 25 minutes

    1. The teacher should begin by giving students the "It's All Absolutely Relative" handout (see attachments). 

    2. The students will begin by ordering the events of their morning in sequential order (first, second, third, etc.). Then students will order the same events using exact times (ex. 6:00 AM).

    3. Next, the students will develop a "working definition" of the terms absolute age and relative age. If students are struggling, the teacher can provide a hint: Putting the events in sequential order (first, second, third, etc.) is an example of relative dating while defining each event with an exact time is an example of absolute dating. 

    Note: The teacher may wish for students to work with a partner to write a "working definition" of each term.

    4. After the students have written their definitions of the terms, the teacher should provide the scientific definitions of the terms and have students write them on their handout. 

    Absolute Age: Geologically speaking, absolute age is the number of years since the rock formed. It can be determined by radiometric dating. (Example: That rock is 1 million years old.)

    Relative Age: Geologically speaking, relative age is stated as an age comparison between two geological formations (Example: That rock is older than this rock because that rock formed first.) 

    During Strategy/Explore & Explain: 50 minutes

    1. For the next portion of the lesson, students should be divided into groups of four to five students each. 

    2. The teacher should give each group a copy of "Geologic Events-Life Forms Cards" (see attachments). The students should work together to cut out the cards and arrange them in chronological order, from the oldest organism to the youngest organism. At this point, the teacher should not correct students' answers. 

    3. After each group orders their cards, the teacher should lead a discussion on relative vs. absolute age. The teacher should ask the students, "Did you order your cards by relative dating or absolute dating? How do you know?"

    Possible Answer: The cards were ordered according to relative age, as we ordered the cards by which organism existed first, next, last, etc. We did not order them by absolute age because we did not order them by their specific geologic age. 

    4. Next, the teacher will provide each group with 4.6 meters of adding machine tape. If this material is not available, the teacher can use toilet paper or tape sheets of paper together until the appropriate length is reached. 

    5. The students should label one end of the paper "Origin of Earth-4.6 bya (Precambrian Era)" (bya=billion years ago) and the other end of the paper "Today (Cenozoic Era)". 

    6. The teacher should give each group the "Geologic Events-Life Forms' Absolute Age" handout (see attachments). This handout will provide the absolute age of each organism. Students will use a scale of one meter is equal to one billion years to place each organism in the correct order on the paper timeline. The students should begin by using the scale factor to determine the correct placement of each organism on the time scale model. The students will find the scaled distance by dividing the absolute age of the organism by the corresponding scale factor (See attachments for teacher key.) Next, the students should find the organism to most recently exist and measure the scaled distance from the end of the paper marked "Today". 

    Example: The first modern humans existed 100,000 years ago. [Using a scale factor of 1 millimeter=1 million years-100,000/1,000,000=0.1 mm] The students will measure 0.1 mm from the end of the paper marked "Today" and place the Absolute Age card for "First Modern Humans" at this location.

    7. The students will continue these steps for the remaining organisms until the oldest organism is placed on the timeline. 

    Example: The first bacteria existed 2.5 billion years ago. [Using a scale factor of 1 meter=1 billion years-2,500,000,000/1,000,000,000=2.5 m] The students will measure 2.5 m from the end of the paper marked "Today" and place the Absolute Age card for "Bacteria" at this location.

     After Strategy-Explain & Elaborate-25 minutes

    1. The students will use both timelines created in the during activity to answer reflection questions about the concepts learned while creating the scaled geologic timeline using the Geologic Time Scale Model Reflection Questions handout. The teacher may let the students complete the reflection questions independently or with group members. The students will need a Geologic Time Scale, such as this "Geologic Time Scale" from  University of California Museum of Paleontology at Berkeley, to answer some of the questions.

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    Assessment Strategies

    Formative Assessment

    The teacher will informally assess students' understanding of absolute and relative age by reviewing each student's "working definition" of these terms in the before strategy. The teacher will informally assess students as they work in groups to place the organisms in order of relative and absolute age in the during strategy. The teacher should discuss student's placement of each organism on the timeline to ensure students understand the difference between relative and absolute age.

    Summative Assessment

    The teacher should formally assess student's reflection questions completed in the after strategy of the lesson. Students' answers to these questions should demonstrate the student's knowledge of relative and absolute age, as well as an understanding of the geologic time scale model created in the during strategy.


    Teachers could identify students who require acceleration opportunities and appoint these students as group leaders for the collaborative timeline activity. 

    Students who finish the independent activities can complete a review activity using the following website: "Geologic Time" from the University of California Museum of Paleontology at Berkeley. 


    Students who need additional preparation before the lesson or extra review after the lesson can complete the activities on the following website: "Geologic Time" from the University of California Museum of Paleontology at Berkeley. 

    View the Special Education resources for instructional guidance in providing modifications and adaptations for students with significant cognitive disabilities who qualify for the Alabama Alternate Assessment.