A couple of weeks ago, Kat and I began our big geology project. We learned a lot about the geological history of Arizona and even took our lessons to the field! While examining the outcrops around us, we talked a lot about the layers of the Earth and plate tectonics. We talked about how layers of the crust may have been thrust upwards as plates moved into each other (uplift) and how some layers would sink under others as they moved lower to the mantle (subduction). However, as I was explaining these concepts to my daughter, I realized that she would have a much easier time understanding it if she could see these geological processes at work. So, we spent an entire week in the kitchen cooking up concepts for understanding geology!
The Earth’s crust is divided into four major layers: the crust, the mantle, the outer core, and the inner core. The Crust is approximately 5-30 miles thick, being the thinnest at the oceanic layer (up to 5 miles thick) and the thickest at the continental layer (up to 30 miles thick). The crust contains all of the dirt, sand, pebbles, rock, and bedrock that we typically think of when we consider the Earth’s crust.
The mantle is approximately 1,800 miles thick and is made up of not-quite-solid not-quite-liquid rock. This thick, viscous rock moves around by convection (as it rises toward the crust it cools, then falls back down to heat up again), which is what moves the plates around on top of it. The outer core is approximately 1,400 miles thick and made up of liquid Iron and Nickel. The inner core is approximately 900 miles thick and made up of a solid, incredibly dense ball of super hot Iron and Nickel.
Now, these are all pretty basic things that we read when learning about the layers of the Earth, but what does it really mean? How do you get a grasp on those distances, those layers, and what that even looks like? The first method we used was by Googling how far each of those distances were from our city. Then we put the two places in Google Maps to get an idea of what that looks like. For us, 1,800 miles would take us all the way to Columbus, GA, which is almost all the way across the continental United States! 1,400 miles took us to Demoines, IA, and 900 miles took us to Cottonwood, CA. Putting these places into Google Maps gave us a great visual representation for how thick each layer of the Earth is and how far we would have to go to traverse those distances.
Once we had the distances covered, what about the layers themselves? What would these layers look like? For this question, we had to get in the kitchen and make ourselves a cake!
A LAYER CAKE OF EARTH
This is where you get to have fun and be creative! Think about the layers of the Earth and what they are made of. Where can you find liquid rock? What about a rock that is flexible and plastic like? Where can you find fossils? Maybe you can play around with adding fossils into the layers of your cake for your kids to dig out. Whatever you decide, be prepared to have fun and get MESSY!
Sponge cake mix (or any sturdy cake mix) and the ingredients needed to prepare it
Small cake ban or bread pan (we used a bread pan)
Non-stick cooking spray
Newspaper or foil to cover your work surface with
Something to use as a liquid layer (we used both icing and butterscotch pudding)
Something to act as rocks and bedrock (we used nuts)
Something to use as dirt (we used cookies)
1. Prepare your cake batter according to the directions on the box. Pour a thin layer (approximately 1/2 inch in your bread pan. If you choose to do so, you can add a few drops of food coloring to color your layer.
2. Bake your half inch cake at the temperature that is recommended in the instructions for your cake mix. We baked ours for 10 minutes, using the toothpick test to make sure it was done.
3. When your cake is done, dump it on to your work surface and add another half inch layer of batter. Color this if you choose, and bake it again for approximately 10 minutes (or until done). Repeat until you have 3 layers of cake.
4. Now it’s time for decorating! One of these layers will be the inner core, another will be the mantle, and the final layer will be the crust. It’s up to you to decide what goes in between all of it! Color your frosting, add pudding, add some chopped nuts or marshmallows for your rocks and fossils. Get creative and get messy!
The final step of course, will be the most fun, as you and your kids get to dig into this gigantic cake of Earth!
Once we finished our model of the layers of the Earth, it was time to talk about Tectonic Plates. Throughout the Earth’s history, the thick land masses have moved around, crashing into each other, pulling away from each other, and forming volcanic rings and deep chasms. We also know that at various points throughout Earth’s history, some or all of the large land masses were connected together. We know this because of unique rock layers on matching coastlines, the fossil record, and because the tectonic plates look a lot like puzzle pieces that could fit together!
We found a really great way to demonstrate this at home and we already had all of the supplies in our kitchen!
MAPPING THE TECTONIC PLATES
Play dough in various colors (We made our own using the recipe at the top of this page)
A map of the tectonic plates (we printed this map, the large boundaries made it easy for tracing)
A labeled map of the tectonic plates (we used this map)
Sharp knife (such as a paring knife)
Pen and paper
1. On a separate piece of paper, write down the names of each tectonic plate. Cut the names out into individual strips and set them aside. You will be using these as labels for your plates at the end of the project.
2. Cut the individual tectonic plates out from the unmarked map. Set these in a pile.
3. Pick out a tectonic plate from your pile. Roll out a piece of play dough so that it will be approximately the same size as your plate. Place the tectonic plate cut out over the dough.
4. Using the knife, carefully cut along the edges of your paper, tracing the tectonic plate into your play dough. As you peel away the excess dough, you should have what looks like a detailed tectonic plate!
5. Compare your play dough pieces to the tectonic plates on the labeled map. When you’ve found the plate that matches yours, grab the piece of paper in the label pile and set it on to your tectonic plate.
6. Once you’ve gone through all of your tectonic plates, piece them together to mimic where they are now. See if they might fit together differently. How would the tectonic plates have looked when the continents were all landlocked together as they were when they formed the supercontinent Pangea?
Finally, we reached the last part of our week of kitchen geology. After talking about the layers of the Earth and tectonic plates, it seemed like a natural progression to go over the three types of rock as well. What better way to get a grasp on Igneous, Sedimentary, and Metamorphic rocks, then to make them in our own kitchen?
The first set of rocks we would be making would be liquid lava Igneous rocks! A good friend of mine at The Ard School of Arts and Sciences provided this adorable and awesome recipe for Magma Candy, which I’ve been given permission to reprint below.
1/2 cup of Karo corn syrup
1 cup of sugar
1 tsp of water
Glass 2 cup measuring cup (one that will withstand high heat)
1. Cover your work surface with foil.
2. Mix all of your ingredients in a heavy 2 cup glass measuring cup.
3. Microwave on high power for 3-7 minutes, depending on the power of your microwave (for us it was 6 minutes)
4. Test your magma! Carefully drop a spoonful of the magma into a cup of cool water. If it forms a puddle or blob, microwave for 1-2 more minutes. If it makes a crackling sound and seems to magically freeze into a shape, you are ready to rock.
Get Creative! After drizzling spoonfuls of magma on to your work surface, add some food coloring and swirl it around. What kinds of swirly color patterns can you make? You can also create works of igneous art by making spun sugar creations. Watch this video for instructions!
Note on Safety: When this “liquid magma” comes out of the microwave, it will be VERY HOT. If it spills on you it will cause burns! The transport of magma from microwave to work area should only be done by an adult wearing oven mitts on both hands. This is a very fun and very easy magma demonstration, but please take precautions!
To clean your cup, simply soak it in sudsy water. After a short while, all of the sugar will be dissolved by the water.
When we were finished playing with (and eating) our magma candy, it was time to clean up and move on to building our sedimentary rocks!
4 paper/plastic cups
Plaster of Paris
Layers of sediment (we used sand, gravel, chalk, and dirt)
Food coloring (optional)
1. Put on your rubber gloves. Plaster of Paris will dry like cement, you don’t want this stuff drying on your skin, or your clothes.
2. Divide your layers into your plastic cups. One cup should house one type of sediment. If you would like to add color to your sand, add 1-2 drops of food coloring and shake to coat.
3. In one of your cups, mix your plaster of paris according to the directions on the package (we used a 2:1 ratio of plaster to water)
4. Beginning with your sand layer, begin mixing your plaster of paris with your layers of sediment. Mix to a desired consistency, make sure you have enough plaster to allow for cementation, but not so much that you completely cover the materials.
5. Mix a small amount of plaster with your gravel. Scoop it out of the cup and layer it on top of your sand. Don’t stir it, as you don’t want to mix everything together. Just past it down with your spoon until you have an even layer. Repeat the process with the rest of the sedimentary layers.
6. Allow your sedimentary rocks to dry overnight. This will be a very sped up process where the sdeiments will bind together with the plaster acting as a glue. What would normally take thousands of years has just happened in your house overnight!
Finally, when we were finished with our sedimentary rocks, it was time to change things up a bit! This next demonstration comes from our home school science classes at The Arizona Science Center. All it takes is some a lot of heat, a little bit of pressure, and a candy bar…
Metamorphic rocks are igneous or sedimentary rocks that are subjected to extreme heat and pressure. In this demonstration, we’ll be subjecting a candy (or granola) bar to these processes in order to force a metamorphic change to our “rock”.
Snickers Bar (or layered granola bar)
1. Break your candy bar in half. Examine the layers of your sedimentary rock.
2. Wrap your rock in aluminum foil. Put your pan on top and press down hard! This will mimic the pressures found deep within the Earth.
3. Open your foil and examine your newly pressed rock. How have the layers changed? Are there any rocks you’ve seen in that remind you of this?
4. Put your pan on the stove and turn it to med/high heat. Rewrap your candy bar in the foil and add it to the pan. Let it heat for 7-10 seconds.
5. Remove the foil from the pan and open it. What happened? As your rock cools, observe how it has changed through heat and pressure.
6. Eat the other half of your candy/granola bar!
These lessons gave me and Kat a better idea about the concepts of plate tectonics, the layers of the Earth, and the three types of rock and how they’re formed. Learning geology out in the field is really fun, but it’s even better when we have a good grasp on how the mountains, rocks, and land masses were formed. Then we can look around and really be able to read the stories that the rocks have to tell.
The best part of all though, was being in the kitchen making a mess and having a great time! We made a monster of a geology cake, magma candy, our own sedimentary rocks, and our own tectonic plates that we got to crash together, all in the name of science! I’d say that’s a pretty great week.