This model for sedimentary rock formation will become a favorite for both you and your students. When creating models with students, we really want them to be as accurate as possible. Students are less likely to develop misconceptions and they gain a deeper understanding for a complicated process.
This model includes all 5 steps involved in the formation of sedimentary rock: weathering, erosion, deposition, compaction and cementation.
We like to have students create notes for their interactive notebook to reference during this lab. Alternatively, you could have them record notes as they progress through the lab.
- cornbread mix (get the just add water kind)
- food coloring to make 3 colors of cornbread
- 3-oz disposable cups
- water in container per group
- pipette/eyedropper per group
- butcher paper/tray for mess per group
- honey or syrup (to mix in to the water)
- plastic storage baggies
- additional Three 3 oz cups per group
- tablespoon for scooping per group
Students will love eating these “sedimentary rocks” when they are finished. If your school or district has restrictions on eating in the classroom, you will need to set exceptions with your students.
Okay, here we go.
Bake 3 different colors of cornbread. If you plan on crumbling at home, bake in regular pans ,however, if you plan on having the students model weathering, bake in mini muffin pans. Plan out about one of each color mini muffin per small group or one tablespoon of crumbled cornbread per person.
If you are “weathering” yourself, put chucks of the cooked cornbread into gallon sized storage bag. Close the bag and then crumble into small pieces to represent sediment. Count out enough of the mini cups so that each group will have 3 (one filled with each color).
Use butcher paper or trays to minimize mess. Pass out the cornbread (muffins or filled cups) to each group along with a small container of honey water and a pipette. Give each student an empty 3 oz cup. If you made muffins, have student’s crumble them into separate cups while discussing how this represents weathered sediments.
Instruct students to put one tablespoon of cornbread into their cup and gently tap the cup on the table. Then, students should choose a different color of cornbread and add that to the cup.
Add just a few sprinkles or very small candies on top of the second layer. Discuss that these represent organisms that have died and will be buried under layers of sediment.
Add the last layer of cornbread on top of the sprinkles. This is a great time to discuss what are the possible outcomes of buried organisms (decompose, form fossils, form fossil fuels). Call attention to the amount of space the “sediments” take up in the cup.
Use a pipette to add 5-10 drops of honey water to the cornbread. Discuss that this models the mineral-rich water that is present in the layers of sediment and give the example of layers of sediment being deposited in a delta.
Use fingers to press straight down on the cornbread. Students should press firmly to make as compact as possible without damaging the layers or the cup. Discuss that this models the compaction of sediment as layers build up.
Tell students that they should try to keep the layers level and not sloped in the cup. Bring attention to the amount of space the “sediments” take up now and discuss how compaction and cementation (honey water) have created new rock.
Turn the cup over and gently press the bottom until the model falls.
Inspect the sedimentary rock model; then, discuss how the layers were formed. Which layer is the oldest and the youngest?
Break the sedimentary rock model in half. Discuss what the sprinkles model. How can we use the layers of rock to determine the age of fossils?
Follow up to sedimentary rock lab:
To follow up this lab, we have students participate in several rounds of Quiz-Quiz-Trade (Kagan, 2009) using Formation of Sedimentary Rock and Fossil Fuels discussion cards. They are able to move around and talk with their peers while talking and using content specific vocabulary. It is the perfect opportunity for correcting any lingering misconceptions.