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Science Lesson in Practice: How Do Sedimentary Layers Form?

written by: Marlene Gundlach • edited by: Wendy Finn • updated: 2/8/2012

Sedimentary layers in rocks are formed from the immense pressure from sediments being deposited from air, wind, ice, rain, and water flow. This lab will help students discover just how these layers are formed.

  • slide 1 of 5

    Prelab Discussion

    Have students read the entire activity and then discuss the following:

    • Review the concept of geologic time. Discuss other processes that take place over millions of years.
    • Review the role of pressure in sedimentary rock formation.
    • Ask students to describe concrete and how it functions.

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    Materials and Preparation

    Materials needed:

    • gravel
    • sand
    • clay
    • graduated cylinder
    • jar
    • water
    • timer with second hand
    • spoon
    • cup
    • diluted white glue solution
    • toothpicks
    • Data table to record sediment characteristics
    • Data record table for observations

    To begin, crumble the clay into particles.

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    Procedure

    1. Fill the jar 3/4 full of water.
    2. Drop in a pinch of one type of sediment. Watch it fall. Time the length of the fall. Record the setting rate in the correct column on your sediment characteristics data table.
    3. Repeat step 2 for the other sediment types.
    4. Hypothesize what would happen in you poured a mixture of the three types of sediment into the jar. Record your hypothesis on a separate sheet of paper.
    5. Measure three spoonfuls of each sediment. Mix them together and pour the mixture into the water. Record the settling order in your data table.
    6. Pour out the excess water from the jar. Measure 50 mL of the diluted white glue solution. Evenly distribute the solution over the sediment layers in the jar.
    7. Set the jar in a warm, dry place.
    8. The next day, use toothpicks to test the hardness of the layers. Continue to keep the jar in a warm, dry place. Observe the layers each day for three days total. Record your observations in your observation table.
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    Analysis

    1. What happened to the glue solution after several days? (Over several days, the glue solution seeped through the layers of the sediment in the jar and hardened.)
    2. What did the glue solution represent? (The glue represents the mineral cements that hold sedimentary rock together.)
    3. What happened to the sediment layers after several days? (The sediment layers dried out and hardened after several days.) Which layer was the first to harden? (The top layer should have hardened first.)
    4. Did the water in the jar represent fast- or slow-moving water? Why? (Slow-moving because it was not flowing over the sediment.)
    5. What kinds of sedimentary rock did you form for each layer? (Conglomerate rock formed.)
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    Conclusion

    Have students write a paragraph describing how this model is similar to the natural processes involved in the formation of sedimentary rock layers. How is it different? (Answers will vary: The model is similar in that different sized particles settle out at different rates, time is needed for the sediment to dry out, and a cement is needed to hold the particles together. Differences include the short time in which "rock" is formed and the cement.)

    For a challenge, as students to develop a model to show how igneous rocks form. Compare this to the sedimentary rock model.

    For additional ideas on teaching about rocks, read "Let's Rock!"