Sorting Out Sedimentation
AbstractSedimentary rock forms in layers that are deposited one after the other over long periods of time. Oftentimes, sedimentary rock contains fossils and other debris that are deposited within the layers. How do sediments form? How are sediments of different shapes, sizes, and types sorted during the process of sedimentation? Find out in this science fair project!
Sara Agee, PhD, Science Buddies
To investigate how particles of different sizes, shapes, and textures are sorted into different layers during the process of sedimentation.
Have you ever seen rocks with distinct stripes of color or texture? If so you've been looking at sedimentary rock. Sedimentary rock forms in layers that are deposited one after the other over long periods of time. The layers are made out of sediments, meaning particles of soil, other rocks, and mineral deposits. The sediments mix with water and eventually settle on the bottom of rivers and streams and form layers. Over geologic time (thousands or hundreds of thousands of years), the layers will harden into solid sedimentary rock. Over two-thirds of the land mass on Earth is covered in sedimentary rock!
If you have a patio at home that is made from flagstone, you have a source of sedimentary rock. If you look closely at the edges of the flagstone, you will see that the rock is made up of many layers. You can even chip away at the layers, sometimes causing a layer to flake off of the surface. Because of the many layers, sedimentary rocks are soft and brittle.
Oftentimes, sedimentary rock contains fossils and other debris that are deposited within the layers. Most fossil formations are found in sedimentary rock. Why? Since sedimentary rock is soft and can be easily chipped and brushed away, it reveals the mineralized fossils within.
The process of creating sedimentary rock is called sedimentation. Sedimentation often occurs where there is a moving body of water. Rivers are usually very active in sedimentation. This is because the rapid movement of the water causes the soil and rocks along the bank of the river to erode, or break away. These sediments are then deposited in other areas of the river. In this episode from DragonflyTV, Margaret and Elizabeth take a canoe trip down a local river to learn where sediment gets deposited and how that changes the shape of the river. What do you think they find out? Watch the video and see for yourself!
How do you think sediments of different shapes, sizes, and types form layers? Do you think they stay all jumbled together, or do they sort themselves in some way? Even though sedimentation takes thousands of years in nature, you can explore the answer to these questions in just a few days in this science fair project.
Terms and Concepts
- Sedimentary rock
- How do sediments form?
- How are particles sorted into layers of sediment?
- What are the characteristics of sedimentary rock?
- Ribokas, B. (2000). The Geology of the Grand Canyon. Retrieved April 25, 2006.
- Wikipedia Contributors. (2006, April 25). Sedimentary rock. Wikipedia: The Free Encyclopedia. Retrieved September 25, 2008.
- Brynie, F.H. Parent's Crash Course: Elementary School Science Fair Projects. Hoboken, NJ: Wiley Publishing Inc., 2005. pp. 165-168.
- TPT. (2006). Rivers by Margaret and Elizabeth. DragonflyTV, Twin Cities Public Television. Retrieved September 20, 2008.
Materials and Equipment
- Mixture of different-sized rock, gravel, sand, and soil particles
- Plastic baggies, sealable
- Permanent marker
- Small plastic water bottle
- Coping saw, have an adult help you use the saw and use caution!
- Digital camera
- A penny, a quarter, a nickel, and a dime
- Photo software that will enlarge photos
- Printer or access to a place that will print an 8x10 photo for you
- Metric ruler
- Lab notebook
- Gather up different sources of particles that vary in size, type, and texture. Good sources of particles are mud, sand, gravel, and rocks.
- Keep the samples separated so that you can go back and look at it later if you need to. Do this by placing some of the material in a sealed plastic baggie and labeling the baggie with a permanent marker. Indicate where and when you found the material.
- Now make a mixture of your different materials by adding 2 tablespoons of each material to another plastic baggie, then seal the baggie and shake to mix the materials together. Label this baggie as your Mixture Sample.
- Prepare the plastic water bottle for your experiment. With an adult's help, cut off the top spout of the bottle with the coping saw. Be sure to wear your safety goggles.
- Carefully pour your mixture sample into the water bottle.
- Fill the water bottle to the top with water. Pour it slowly into the bottle so that the particles have time to absorb the water and don't float out of the bottle.
- Cover the top of the bottle completely with your hand and shake it approximately 20 times up and down to thoroughly mix the particles and the water.
- Set the bottle down in a safe place indoors, where it won't get knocked over or bothered by another person, and leave it undisturbed for a few days, or until all of the water has evaporated. It is best to leave the bottle in a sunny place to help the water evaporate and the layers to harden.
- When you can see that the water is completely evaporated and the soil is hard, you are ready to cut open your bottle. Have an adult help you cut the bottle lengthwise in half with the coping saw. This will reveal a cross-section of the layers that formed in the bottle.
- Arrange the bottle halves and the penny, nickel, dime, and quarter on a light-colored surface in a well-lit area, like a concrete patio or sidewalk.
- Use your digital camera to take a picture of the bottles and the money. Take several pictures so that you can choose the best one.
- Use photo editing software to crop and enlarge your photo as much as possible. Then print your photo as a large 8x10 image, either at home or at a photo kiosk.
- On your photo, label the layers with numbers, with layer 1 being at the top surface, and numbering until you reach the bottom layer.
- Using a metric ruler, measure the width of each layer and piece of money in your photo, using millimeters (mm). Write the measurements in a data table, like this one:
|Layer||Thickness (mm)||Description (color, shape, consistency, etc.)|
- Using your picture and your baggies of starting material, compare each layer to the original sources. Does the number of layers that formed match the number of sources? Do any of the layers look like one of the original sources? Do any of the layers look like a portion of one of the original sources?
- Think about the different thicknesses and ordering of the layers. Is there a difference between things that ended up on the bottom compared to things that ended up at the top? Which layers do you think settled first, or last, and why?
Ask an Expert
- In this science fair project, you measured the size of each layer from an enlarged photo. How can you figure out what the actual size of each layer is? Use the actual size of the coins in your photos to calculate the actual size of each layer of sediment. Here are the actual diameters of U.S. coins: penny (19.05 mm), nickel (21.21 mm), dime (17.91 mm), and quarter (24.26 mm). Do the calculation by dividing the actual size of the coin by the size of the same coin in your picture, and then multiplying this number by the size of the layer in your picture. For example, if the size of a nickel in your photo is 36 mm, you would multiply each of your layer measurements by 1.7 to get the actual measurement in mm.
- You can use a similar test to characterize soil types. Make more bottles and use them to collect soils from different places. Label each bottle and fill half full with a sample, add water, cover and shake. After drying, you can cut open and compare the different samples. Does the pattern and number of layers change or stay the same from sample to sample? What do the layers tell you about the soil?
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