**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.