Kids Activity: Let's Make Sedimentary Rocks

by Staff

magnifying glassWould you like to be a detective -- unraveling a mystery of what the world was like hundreds, thousands, and even millions of years ago? One tool for your investigation is sedimentary rock layers. They're often found in plain view outside, particularly around canyons, water sources (oceans, rivers, or creeks), or even along the highway where road construction has blasted through a hillside.

If you look closely at a piece that has broken off you will likely find small shells, imprints of leaves, bugs, and in some cases footprints (watch out for those from dinosaurs)! You may also notice ripples in the rock. These could have been formed by the movements of water, wind, or sand. Who knows what you will learn about the world around you!

Sedimentary Rocks

What are sedimentary rocks and how are they formed? Sedimentary rocks are made of layers of small particles of sand, mud, and any type of rock located at the earth’s surface. They are unique in that unlike their igneous brothers formed in the heat of the earth's core, sedimentary rocks are made in far cooler conditions, typically under water.

Over time, these particles are broken down by various weather elements over time and often deposited in one of the earth's water sources. There they settle to the bottom as sediment. Minerals found within the water serve as a bonding agent to harden. As time passes and the process continues, new layers are formed. As the weight and pressure builds, these layers squeeze together and create new sedimentary rocks!

These rocks can give us clues to what life was like long ago. They are the only type of rock containing fossils. What can you learn as you study sedimentary rock layers? They contain information on the world's climate, plants and animals, and even wind patterns at that point in time ages ago.

We also depend upon sedimentary rocks as a source of water and oil used for fuel, heating, and more.

Let's Experiment!

While you may not have thousands of years to wait, you still get an idea of how these rocks are made by creating some of your own! Besides, who doesn’t like the opportunity to play with food coloring, sand, miniature shells, and other neat stuff? Below you will find two fairly simple experiments to launch your budding geology career (or at minimum, encourage further interest in that rock you were going to throw)! Let’s get started:

Quick and Easy Sedimentary Rocks
colored sand, dryingWhat you'll need: Sand, food coloring, Ziploc baggies, funnel, and a clear glass jar.

What you'll do: Divide the sand into the bags. How many bags/how much sand in each depends entirely on how many layers you want to make. Some layers can have more sand than others, too. Generally, five to ten layers is reasonable.

Carefully add the food coloring to each bag one drop at a time. The more drops you add, the darker the color change will be. Keep in mind that you can always add more drops if you want it darker. Tip: Get creative! Try mixing different drops to discover what new color you can come up with!

Seal each bag and shake until sand is dyed. After you are satisfied with the color in each bag, dump each bag of colored sand into a separate dish so it can dry for a few hours or overnight. Tip: Darker colors tend to require longer drying times.

Dump each baggie of colored sand into a separate dish so it can dry for a few hours or overnight.

Finished layersPour sand carefully into jar in layers. If the jar's mouth is small, you may want to use a funnel. Tap lightly to settle the sand. Can you tell me why you shouldn't shake it? That's right, the layers will mix.

Can you use anything besides sand? Sure! Try adding small rocks, tiny seashells or other things for different kinds of layers and textures. One child added a layer of salt and one of couscous). What do you think would make an interesting sedimentary layer?

The More Permanent Way

What you'll need: A plastic spoon, plaster of Paris, food coloring, scissors, sand, gravel or other layering stuff, a plastic bottle, small shells, bags for coloring sand, cups or bowls for mixing, petroleum jelly.

What you'll do: Decide what order your sedimentary rock will be formed. Mud first? Use a finer sand or even a silty soil. What next? Maybe broken seashells or a limestone layer (broken chalk is perfect). Once you've decided on your layers, get started!

Will you be using small sea shells? If you coat them with petroleum jelly, your rock layers may have impression "fossils."

Mix food coloring and damp sand in a zip lock plastic bag. When you're color is just right, fill your mixing cup 2/3 full. Fill to top with plaster of Paris and water solution (follow plaster of Paris box directions). Carefully pour as much of this layer as you want in your plastic bottle. Use a funnel if needed.

Prepare your next layer by filling your mixing cup 2/3 with "sediment" and the rest of the way with plaster of Paris and water solution. Layer this mixture in the plastic bottle. Fill the bottle, alternating sediment as you go along.

Let the bottle rock harden for a few days or at least a few hours. Then cut the bottle apart with the scissors. Can you see the layered sedimentary rock? If you like, break the layers of the sediment apart and you may be able to see shell imprints or "fossils" and their imprints.

Even More Examples

All good scientists know that it is very important to put newly learned principles to work within everyday life to help with visualization and greater understanding! Did you work up an appetite? Maybe you and mom should make seven-layer dip to go with tortilla chips or a batch of layered granola bars. Just remind her that hands-on experience is necessary -- all in the name of science! You may also want to mention that you are willing to share!

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