Students Make a Model of the Ocean Crust and Then Eat It
NPR’s weekly science program Science Friday recently created a video that shows the layers of the ocean floor using various unhealthy, but delicious food items to represent the layers. This video is an excellent introduction for students to the science of our current expedition that can also be expanded in a hands-on way in the classroom by having the students create their own models of the ocean floor, using food or other items they feel are representative of the different layers.
The “Drilling to the Mantle of the Earth” video makes reference to this expedition (though not by name) and also discusses why as yet scientists have not drilled all the way to the mantle. Along with the fun graphics, the video is also an interview with Doug Wilson, one of the scientists on board the ship right now (to see the entire science party, visit here).
After watching the video, students can make their own model of the ocean crust similar to the one in the video. Here are a few things to know about each layer that can help them determine what materials to use.
The Ocean: Don’t forget that the crust is under a lot of water, which is part of what makes drilling the ocean floor such an amazing accomplishment. Right now the ocean floor we are drilling in is 3635 meters below us from the ocean surface to the floor (11,925 feet).
Sediment Layer: Near the coastline, sediment layers in the ocean are often mainly sands, silts and clays eroded from the continental crust. Farther out from the coast they are more likely to be shells from microscopic marine organisms such as foraminifera.
Lava Flows (aka Basalt Layers): These are the rock layers at the top of the ocean crust that are almost always the rock called basalt. They are formed when the magma rises up from the asthenosphere at the spreading center of the ocean plate and then flows out over the top of the ocean floor and quickly cools into rock (remember when magma reaches the Earth’s surface, it becomes lava).
Sheeted Dikes: Dikes and sills are intrusions, places where magma is able to rise up through fissures in the lower layers of the crust and cool into rocks. Intrusions are always younger than the rocks around them. Intrusions within the ocean floor sometimes form basalt and sometimes form gabbro.
Gabbro: Gabbro is the type of rock that forms when magma cools (as opposed to when lava cools). It is the same chemistry as basalt, because both are made from the same magma, but gabbro has much larger crystals because it cools at a slower rate than the lava that forms basalt when it comes in contact with the cold ocean water. Gabbro forms at the bottom of the ocean lithosphere when the magma that is touching the plate slowly cools into gabbro rock.
Mantle or Asthenosphere: You might want to call it lithosphere and asthenosphere instead of crust and mantle. The crust and mantle are names to describe layers of the Earth based on changes in chemistry. Lithosphere and asthenosphere are layers based on changes in physical properties of the Earth. The lithosphere is the outer hard, rocky layer of the Earth and the asthenosphere is the molten, plastic, magma layer beneath the lithosphere that is about the consistency of Silly Putty.
A couple other ideas that may be helpful in your teaching:
The Science Friday website is a great resource for teachers who want to introduce their students to what is currently going on in scientific research. It includes podcasts of the weekly radio programs that feature interviews with scientists that rarely become too technical to understand, videos that complement the main science features of their shows for all us visual learners and hands-on science activity ideas for educators to use with their students. (Another great NPR show about science that you might want to check out is Radiolab).