National Teachers Enhancement Network: Lesson Plan

Lesson Plan: Geologic Time: Relative and Absolute Dating
Subject: Earth and Space / Geology / Dating Methods
Classtime:
Total: 5 class periods (50-minute periods)

1 (research the methods)
3 (research eras, construct timetables)
1 (present projects)

Grade Level: 9-12

Materials/Technology:

computer(s) with Internet access (optional)
printer (optional)
examples of geologic timetables (from books or the Internet)
science journals/learning logs

Safety, Handling, Disposal:
If using the Internet, close supervision is strongly recommended. Inappropriate sites are easily accessed either by mistake or on purpose.

Learner Outcomes:
Students should be able to:

Define relative dating and describe the law of superposition.
Define absolute dating and describe radiometric dating methods.
Differentiate between relative and absolute dating.
Apply knowledge to construct an accurate geologic time scale.

Problem/Purpose:
The purpose of this geological exploration is to have students investigate relative and absolute dating; determine the difference between the two dating systems (including methodologies used to acquire dates); and apply this knowledge by creating a geologic timetable of their own.

Background/Inquiry:
The geological events in Earth's history are a series of episodes. Geologists use two scales to date these episodes and to measure the age of the Earth. One scale records relative time. The other scale measures absolute time. Both scales help describe the geologic record.

Relative time places events in a sequence but does not identify their actual date of occurrence. It indicates age in comparison with other events. The relative time scale is based on the sequence of layering of the rocks and the evolution of life.

Absolute time identifies the actual date of an event. Geologists use the radiometric time scale which is based on the natural radioactivity of chemical elements in some of the rocks. In addition to identifying the actual age of an event, absolute time is important for another reason: if the actual time of two events is known, the length of time between the two events can be calculated. Such values make it possible to determine the rate at which a geologic process such as mountain building occurs.

Absolute time might seem more important than relative time because absolute time gives an actual date, but absolute dates are difficult and expensive to obtain. Most geologic work is done using relative time.

Vocabulary List: Here.

Hypothesis:
N/A

Procedure:
This procedure can be done with or without computer(s). The information is accessible from many different sources.

Grouping or non-grouping of students is deferred to the classroom teacher.

Store information gathered by students electronically (if using computers) and/or have students record it in their journals/learning logs.

Study a geologic timetable, one can be found in many books and encyclopedias or it can be found at various web sites including:

U.S. Geological Survey Publication: Geologic Time by William L. Newman: http://pubs.usgs.gov/gip/geotime/contents.html

U.S. Geological Survey Publication: Fossils, Rocks, and Time by Lucy E. Edwards and John Pojeta, Jr.: http://pubs.usgs.gov/gip/fossils/contents.html

*Note: At this site, there is also the opportunity to Ask a Geologist: http://geology.usgs.gov/ask-a-geo.html

Investigate the law of superposition (this information can also be found on the USGS site). Retain access to a version of the geologic timetable and any pertinent information on relative dating (print, store electronically, keep the book handy).

Investigate information on radiometric dating: http://pubs.usgs.gov/gip/geotime/radiometric.html
Retain access to this information on absolute dating (print or store electronically) for later activity.
Conduct a general search (using the Internet or library resources) on each of the eras on the geologic timetable and look for individual events that occurred during each era.

Determine if these events were placed in time by relative or absolute dating. Have students include notes detailing the reasons they think these events were placed in time by either (or both) of the two dating schema.

Students organize these events into a geologic timetable of their own. Students should:

Create a table that includes at least two researched events in each era (include all eras detailed in standard geologic timetables) that can be verified using both relative and absolute time. Timetables should be clear and easy to understand.
Include detailed information for each event that provides:

A brief description/summary of the event itself.
Evidence supporting which dating method seems superior in placing the event in time.
Explanation(s) detailing how one dating method supports the other one.

After constructing personal timetable and researching dating methods, students should group materials into a portfolio to be handed in to instructor for evaluation.

Results/Analysis:
Students should present their project (poster, paper, computer generated slide show, etc.) to the class.

Teachers should facilitate classroom/group discussion.

Examples of introductory questions for group discussion are:

What are some of the possible inaccuracies to both dating methods?
How have dating technologies improved over the last 100 years?
What is the possibility of current, accepted information being incorrect due to erroneous dating? An example might be the approximate date of the land bridge between Asia and North America.
What are some significant geologic events that have been placed in time in the local area due to relative dating methods?
What are some significant geologic events that have been placed in time in the local area due to radiometric dating methods?
What are the advantages and disadvantages of each type of radiometric dating method?

Conclusions:
N/A

Assessments: (if included)

Students choose one of the options and perform the task.

Choose a particular geologic event and its date. Tell whether it was dated by absolute or relative dating. Write a short description of the event and justify your reasoning.
Using the geologic timetable found onthe USGS home page, find a relative dated event or an absolute dated event for each of the eras (Precambrian, Paleozoic, Mesozoic, and Cenozoic). Each date should place a geologic event. Tell whether each date is relative or absolute and why.

Integration: (if included)

Reflections:
Share your thoughts on this lesson with the NTEN team.

Please send an e-mail to Patti Harrison.

Extensions: (if included)

References/Resources: (if included)

Advanced Cognitive Tools for Learning: Learning Research and Development Center: University of Pittsburgh: http://advlearn.lrdc.pitt.edu/belvedere/materials/index.html
U.S. Geological Survey Publication: Geologic Time by William L. Newman: http://pubs.usgs.gov/gip/geotime/contents.html
U.S. Geological Survey Publication: Fossils, Rocks, and Time by Lucy E. Edwards and John Pojeta, Jr.: http://pubs.usgs.gov/gip/fossils/contents.html
Ask a Geologist: http://geology.usgs.gov/ask-a-geo.html

Credits
Contributing Teacher: Brian Bedford
NTEN Course: Internet-Based K-14 Earth Systems Science Instruction
Instructor: Jerry Nelson
Assistant Instructor: Bill Ochs
Developing Team:
T.L. Buck Buchanan, Cathy Hensel, Patti Harrison, John Usher, Don Wilson
HTML Programmers: Christy Cousineau, John Usher, Ching-Kwong Chia

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