Learning how sedimentary rocks are made is among the most fundamental concepts in geology. If you want your students or your child to have a firmer grasp of what sedimentary rocks are and how they form, engaging them with experiential learning and hands-on activities can be a game-changer.
Montessori Laboratory offers a free sedimentation lesson (and accompanying experiments) to help you teach about sedimentary rock formation in a fun and hands-on way.
What Are Sedimentary Rocks?
We see sedimentary rocks all around us. These rocks are formed by layers of sediments. Sediment is any particle or material that is moved from one place to another and settles in that new place. For example, if a river picks up bits of dirt while it flows through the river bed, and then those bits settle into the bottom of a lake at the end of the river, these bits would be called sediment.
Sedimentary rock forms much of the land we see today. For example, if you look at the Grand Canyon and see layers and stripes of all different colors, it’s because that rock was formed when layer after layer of sediment settled on top of each other.
How Sedimentary Rocks are Made: An Overview
Like many other aspects of the planet, sedimentary rock formation is also affected by humans and the way we treat Earth. By teaching children about sedimentary rocks and how materials on the surface of the ground turn into long-term parts of our planet, we can pass along a greater understanding of why responsible care for the Earth is so vital.
To help you start planning your lesson, let’s jump into an overview of how sedimentary rocks are made. We can break down the process into four basic stages or components.
Stage 1: Existing Material
Sedimentary rock formation begins with existing material. That can include soil, rock, material from once-living organisms, and essentially, anything else that finds its way onto the ground.
Stage 2: Water Flow
The process of how sedimentary rocks are made continues when water starts to flow. When rain and other forms of precipitation happen, the water flows from areas of higher elevation to lower elevation. As this happens, the water picks up particles of material (like the dirt and remains of living organisms) along the way.
Take a mountain for example. When rain hits the top of the mountain, it starts to flow down toward the bottom. As it does, it picks up some of the dirt from the top of the mountain and pulls it down toward the bottom of the mountain. This often happens in very small or even microscopic amounts at a time, so we can’t always see this while it’s in motion.
Stage 3: Settling Sediment
When water picks up a material and brings it along as it flows, that material doesn’t stay suspended in the water forever. Because the material is denser than the water, gravity eventually pulls the material down so it settles into the ground below the water. When this happens, that material has become sediment.
To some degree, this sedimentation happens along the water’s flow path. If you look along the outer edge of a road after a rainstorm, for example, you’ll see some dirt and leaves that dropped off along the edge of the water as it was flowing along the curb. Eventually, though, the water reaches a point where it stops flowing – in nature, this is often a body of water like a lake, while in our example of the road, it’s typically a storm drain. When the water stops flowing, the remaining sediment settles at the bottom.
Stage 4: Rock Compression
Once sediment has reached its resting place, it stops moving and sits in place. The next time water brings more sediment to that lake or resting place, the new layer of sediment that came with it will settle on top of the old sediment. This process repeats, little by little, over the course of many years.
Each time a layer of sediment settles on top of the old layers, it adds weight to the layers below it. That compression gradually turns the lower layers of sediment into a harder and more solid form, until they eventually become rock.
This is why, when we see sedimentary rock in areas like the Grand Canyon, we can see distinctive layers that have different colors and textures. Each of those layers formed from sediment and tells us what the soil of the area was like at the time.
In the sedimentation lesson from Montessori Laboratory, you can watch a video that goes through the whole process of how sedimentary rocks are made including a demonstration that models how sedimentation and layering happens over time.
Experiments and Activities for Teaching children About Sedimentary Rocks
Teaching children about sedimentation and sedimentary rock formation can often best be done through experiments and activities that allow them to see the process in motion. While it takes long periods of time for sedimentary rocks to actually form, there are plenty of ways to give children a hands-on experience that will introduce them to sedimentation and sedimentary rock formation.
Make a Sediment Jar
One way to help children see how sediment settles is to have them create a sediment jar. This experiment is simple and only requires materials you probably have already: a clear jar like a mason jar for each child, a lid for each jar, water, and dirt.
To start, have the children gather dirt from outside and fill their jars about halfway up with dirt. Any dirt they can find will work, but it’s best if they can get a variety of types of materials in it together. For example, they might pull some topsoil from the playground, some sand from the sandbox, and so on.
Next, fill up the remainder of each jar with water. Close the lid tightly and have each child shake up their jar to mix the dirt and water together.
After shaking for a few seconds, have the children take a look at their jars and take a note of what they see. It probably looks like a very loose, liquid mud that’s all roughly the same color.
Next, have them wait for ten minutes and look at their jars again, noting what they see. At this point, they can probably see that some of the sediment has started to collect at the bottom, and the water at the top of the jar will be lighter.
After this, have them leave the jar for an hour and then take note of its appearance again. By this time, most of the sediment has probably settled at the bottom of the jar, and the water at the top should be much more clear.
This lets children see how, over time, more and more sediment settles at the bottom of a body of water. If they were able to get a variety of materials into their jars, they may also be able to see that the densest materials settled at the bottom.
As a bonus, depending on your students’ or children’s ages and advancement levels, you can segue this experiment into other lessons too, such as tying it to lessons on gravity or density. You can also take the experiment a step further by having students open their jars and leave them in sunlight until the next day so they can see the effects of evaporation.
Use Candy to Form a Sedimentary Rock
Another handy experiment to demonstrate the layers in sedimentary rock is helping children create their own “sedimentary rock” out of candy.
You want to start with some kind of hard candy that comes in different colors, like Jolly Ranchers or Lifesavers. Put a few candies of the same color into a bag and use a hammer to break them into tiny pieces, almost making them sand or gravel. You’ll end up with several colors of this candy “sediment.”
Next, have the children get a plastic beaker or cup, and pour one color of candy sediment into the bottom. They should then do the same with another color, and another color. You can do as many colors as you like but 4-5 colors will give children a good view of sedimentary layering.
Once all the layers are inside the cup, put something heavy on top of the top layer, like a weighted ball or a can of food. Leave this sit overnight.
The next day, have students take off the weight and gently pull their candy “rock” out of their cups. They’ll be able to see distinctive layers, and this gives you an opportunity to demonstrate how the oldest layer ended up on the bottom of the rock, with the newest layer on top. This gives them a view of how scientists use sedimentary rock to learn about different eras in our planet’s history.
Make Teaching About Sedimentary Rocks a Hands-on Experience!
Sedimentary rock lessons give your students a strong foundation in geology that can spark a lifelong love of learning. Getting hands-on brings this concept to life and can spark interest in other related subjects too. Make sure to take a look at Montessori Laboratory’s lesson on sedimentation to get instructions to the experiments we mentioned in this article, print out a sedimentary rocks research prompt card, and to learn more about sedimentation.
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