Before/Engage:
- Show students one or more fossils found in Alabama or show the McWane Center fossil shark tooth collection. Tell students that the official state fossil of Alabama is an ancient whale and display the Encyclopedia of Alabama site. Ask students how shark teeth are found in central Alabama, far from the ocean.
- Give each student a yellow sticky note. Have each student write his or her name on the note. Students should make a graph of their initial ideas about how the fossils were found in central Alabama by placing their sticky notes on the “How Marine Fossils Were Discovered in Central Alabama” chart. This graph can be used as an informal pre-assessment of their understanding of fossils and plate tectonics.
During/Explore/Explain:
- Divide students into heterogeneous groups of 4. Ask, “What makes land change over time?” Have students discuss the question in their groups and share ideas with the rest of the class.
- As students share ideas, expand on each one or add to their ideas by explaining that volcanoes can eject lava to form new mountains or rock formations, erosion and weathering can break down rocks by slowly washing them away and depositing sediment elsewhere to form new rocks, and the earth’s tectonic plates can move, making landforms rise or sink above sea level.
- Tell students they will model what happens when rock formations change over time. Distribute materials to each group: 1 cup vinegar, 1 cup baking soda, 1 cup sprinkles, 1 empty cup, 1 sheet blank paper, 1 toothpick, 4 balls of playdough in different colors, 4 straws, 1 plastic knife, and 1 paper towel. Have students sort the sprinkles into piles based on color.
- Ask students if they know what happens when vinegar and baking soda mix. (There is a reaction; it fizzes or foams up.) Tell students that they will mix vinegar and baking soda in the empty cup to simulate a volcano. The vinegar and baking soda they received should last for four “eruptions,” so caution students not to use all their materials at once.
- Place the empty cup in the center of the blank paper. Pour about a teaspoon of baking soda into the cup, then add vinegar until the cup starts to overflow. Once the reaction stops, trace around the puddle on the paper with a pencil. Dry the paper with a paper towel. Use one color of playdough to simulate the lava that erupted from the volcano. Cover the sides of the cup and the area inside the pencil line with a thin layer of playdough. This represents the igneous rock formed when the lava cools.
- Have students sprinkle one color of sprinkles over the playdough. This represents the plants and animals that lived during the time these rocks were formed. Press the sprinkles in slightly and discuss how some fossils are imprints left in mud that became rock over time, and other fossils are made of bones that fossilized over time.
- Repeat the “volcanic eruption” process three more times. Each time, the students should trace the outline of the eruption with a toothpick, add a different color of playdough to represent the new rock from the eruption, and add a different color of sprinkles to represent the plants and animals living during that time. Point out that the eruptions are not uniform; sometimes there may be a large area covered by the new rock and sometimes it may be a small area. This means that sometimes fossils (sprinkles) from one time period will mix with those of another time period, and other times they will be separated by layers of rock.
- Tell students that rock can be worn away by moving water. Over time, a river or stream wears away the rock in its path. Have one student cut a path through all the layers of playdough to reveal the layers of rock stacked on one another. Ask which layers are the oldest (the bottom ones) and which are the newest (the upper ones).
- Have each student take a “core sample” by pushing a straw straight down through the layers of playdough. The playdough will stick inside the straw. By gently squeezing the straw right above the playdough, students will be able to extract a sample that contains several layers of “rock.” Have students discuss the following questions in their small groups:
- Did everyone’s sample look the same? Why or why not?
- Did all the samples contain fossils (sprinkles)? Why or why not?
- How could some samples prove that organisms lived here long ago, even if they are no longer found in this area?
After/Explain/Elaborate:
- Read Gadsden Times Article “Miles from Ocean, Creek Contains Reminders of Prehistoric Sharks.” (You may print this article for each student and have groups read the article together, or you can display the article for whole-class guided reading, depending on the needs of your students.)
- Discuss how shark teeth could be found in North Alabama using evidence from the text. (For example, “During prehistoric times, the area around Tuscaloosa and points south was covered with ocean waters, greatly diminishing the chance of finding remains of the great dinosaurs that once ruled the earth.”)
- Give each student a blue sticky note. Students should write their names on the notes and post them on the “How Marine Fossils Were Discovered in Central Alabama” graph, forming a new column next to the blue pre-assessment column.
- After discussing the ideas represented on the graph, have each student draw a picture and write a paragraph to explain how rock layers and the fossils show that the earth changes over time. Encourage students to include fast processes (such as volcanic eruption) and slow processes (such as erosion) in their explanations.
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