Rock Layers Lab

Transcription

1 Rock Layers Lab Name: 4th grade PSI Science Experiment Questions How are different sediments deposited differently? How do sedimentary rocks form? Before You Begin Do you think that all sediments settle to the bottom of a liquid in the same way? Why or why not? What do you think makes rock layers different from one another? How might the sediments in different layers be different from each other?

2 Purpose During this experiment, you will observe sediments sinking to the bottom of water. This simulates deposition, the first step in sedimentary rock formation. You will then create a model of a sedimentary rock, using the information you have learned about sediments and how they are deposited. In nature, sedimentary rocks do not form quickly; it is a process that happens over hundreds of thousands to millions of years. In this experiment, you will simulate this process in a few days to find out more about sedimentary rocks and the process of their formation. Materials (for each station) gravel sand top soil graduated cylinder water spoon stopwatch / timer small bowl plastic water bottle, cut in half (bottom half) watered-down white glue toothpicks

3 Procedure How Sediments Settle 1. Observe the clay, gravel, and sand that you have. Record notes about the different sediment sizes on the Sediment Characteristics table below. (You may try to trace a piece of sediment, or measure it, or you may comment on its size in relationship to the other sediments. 2. Fill the graduated cylinder about 3/4 full of water. 3. Drop a small spoonful of one type of sediment into the water; observe it as it falls. Write short notes about your observations in the observations column on the Sediment Characteristics table. 4. Drop another small spoonful of the same type of sediment into the water; use the stopwatch to time the length of the fall. Record the times in the settling rate column on the Sediment Characteristics table. 5. Repeat steps 3 and 4 with the remaining two sediments. Hypothesize: What do you think will happen if you pour a mixture of the three types of sediment into the water? 6. In a small bowl, mix together three spoonfuls of each sediment.

4 7. Pour the mixture into the water. Observe closely as the sediments fall. Record the settling order in your data table, using 1 to indicate the sediment that settled first. SEDIMENT CHARACTERISTICS sediment type sediment size observations settling rate settling order clay gravel sand Did the three sediments settle in the same order when dropped in the water together as they did when dropped in separately? Why do you think?

5 Sedimentary Rock Model 1. Pour a few spoonfuls of the sediment you found to settle the fastest (#1 in the settling order column) into the water bottle. This should be enough sediment to form a good layer in the bottom of the water bottle (about 1-2 cm). 2. Pour a few spoonfuls of the sediment you found to settle slower (#2 in the settling order column) into the bottle on top of the first sediment. 3. Pour a few spoonfuls of the sediment you found to settle the slowest (#3 in the settling order column) into the bottle on top of the other two sediments. 4. Pour the glue mixture gently into the bottle of sediments, making sure to cover the top layer of sediment but using as little as possible to do so. 5. Leave the bottle to sit for one day, preferably in a warm, dry place. 6. After one day, use a toothpick to gently test the hardness of your rock. Observe your rock closely. Draw a picture of what you see in the box labeled Day Let the rock sit and harden another day. Observe your rock closely. Draw a picture of what you see in the box labeled Day 2. DAY 1 DAY 2

6 Lab Questions 1. What happened to the glue solution after two days? 2. What does the glue solution represent? 3. What happened to the sediment layers after two days? 4. Which layer was the first to harden?

7 Conclusion 1. How is this sedimentary rock model is similar to the natural processes involved in the formation of sedimentary rock layers? 2. How is it different?

8 TEACHER NOTES This lab is best done in small groups. The number of students in each group can vary depending on various factors. Every group will need all the materials for the lab. If possible, students can try to remove the water bottles from the sediments after a day of sitting, leaving a more true rock. Note: you may want to poke a few small holes in the bottom of the water bottles before students begin making their rocks, as this will allow air to flow in and dry out the glue from both directions.

9 Answer Key Answers to the Lab Questions: 1. What happened to the glue solution after two days? Over two days, the glue solution seeped through the layers of the sediment in the bottle and hardened. 2. What does the glue solution represent? The glue represents the mineral cements that hold sedimentary rock together.) 3. What happened to the sediment layers after two days? The sediment layers dried out and hardened after two days. 4. Which layer was the first to harden? The top layer should have hardened first. Answers to the Conclusion Questions: 1. How is this model is similar to the natural processes involved in the formation of sedimentary rock layers? Different sized particles settle out at different rates. Time is needed for the sediment to dry out. A cement is needed to hold the particles together. 2. How is it different? We did not model the pressure that compacts the sediments. In nature the cement is formed from salts left after water has been squeezed out of the sediments. Our experiment only took two days, while it usually takes many years.