1. On the board or on a sheet of chart paper, write the word fossil and ask students to define the term. Record their responses. Then have students answer the following questions to help define the term:

1. What is a fossil?
2. What can become a fossil?
3. How do fossils form?

2. Tell students that they will now create their own fossils. Begin by giving each student a paper plate filled with wet plaster of Paris. Have them take the natural objects that they brought from home (or that you have provided to them) and press them into the plaster. Once the impressions have been made, they can remove the objects from the plaster. Remind the students to be careful not to touch the plaster, as it will need time to harden and dry. Then ask students to write down some initial observations about their fossils. For example, they should consider which parts of the objects made very visible impressions in the plaster, and which ones are harder to see. When they are finished recording their observations, have students set aside both their fossils and their notes so they can refer to them later in the lesson.

3. (Optional Activity) Show the Becoming a Fossil QuickTime Video. It depicts how the Australopithecus afarensis skeleton known as Lucy could have been fossilized. Discuss the following questions:

1. How do scientists think that Lucy may have died?
2. What made her bones turn to stone?
3. What natural events made it possible for her fossilized bones to be discovered?

You can re-enact the process during the discussion (or have students do so) by filling a box with Earth materials, putting a doll in it, covering the doll with more material, and then shifting the box until the doll is exposed.

4. Show the How a Dinosaur Became a Fossil Flash Interactive and the Laetoli Footprints QuickTime Video. Discuss with students how the fossilization of the dinosaur differs from the footprint. Which one is similar to the type of fossil created by Lucy? Which one is similar to the fossil model that they just made? Students should begin to reflect on the difference between a body part fossil and a trace fossil.

5. Now that students have explored how a fossil forms, they can begin to understand what scientists can learn from examining a fossil. Project the Fossils Flash Image and discuss each image with the class. Emphasize how fossils are a record of the plants and animals that lived a long time ago. As you look at each fossil, discuss the following questions:

1. Is this a plant or an animal fossil?
2. What do you think this plant or animal looked like when it was alive?

6. Divide the class into pairs, and have them explore the Fossils: An Ancient Sea in Indiana Flash Interactive. Encourage them to take their time and explore all the links and concepts. Tell them to pay particular attention to the three types of fossils: trace, soft tissue, and hard parts of plants and animals. Encourage them to take notes that they can refer to later.

7. Fossils can tell us about more than just the plants or animals that made them. Ask students to quickly brainstorm what else they think we can learn from fossils. Let them share a few of their ideas. Then pose the question, How many of you think that parts of the United States were once covered by an ocean? (It was.) How might scientists have discovered this? Show the The Grand Canyon: Evidence of Earth's Past QuickTime Video. Discuss how we know about changes to the environment because of the fossils found in the Grand Canyon.

8. Divide the class into pairs again and ask them to navigate the Types of Fossils Flash Interactive. Again, encourage them to take their time reading the information on each page. When they are finished, ask each pair to join with another pair to form a small group. Assign each group one of the scenarios below, or develop your own, featuring different types of organisms in a particular environment.

Sample scenarios:

1. a worm living in a rainforest
2. a polar bear running across a snowfield in the Arctic
3. a fish swimming in a lake
4. a snail living in a rainforest
5. a snake crawling through a desert
6. a tree growing in a swamp
7. a deer living in a forest

Have each group present its scenario to the class. Tell them that they will need to answer the following questions:

1. Based on its characteristics and the environment in which it lives, do you think the organism has the potential to fossilize? Why or why not?
2. If so, which of the organism's characteristics do you think will be visible in the fossil?
3. If not, what do you think would need to be different about the organism's environment to make it more likely to fossilize?

9. To conclude the lesson, ask students to review their original definition of fossil and revise it, as needed, based on what they have learned. Record the new class definition on the board or chart paper.