How to Get From Here to There

The students will use their prior knowledge of the structure of the Earth. They will observe a demonstration of convection with different materials. They will incorporate this with the idea of plate tectonics and share their thoughts with a group to come up with their own theory with evidence to back up their thinking.

This is a mid topic lesson for eighth grade students in classes of approximately 24. They will work in groups of 3-4. During this time they will have had the opportunity to study and sketch the structure of the Earth. They will watch and discuss a demonstration with three different liquids that will demonstrate that the rate of convection is different with different materials. I will need water, corn syrup, rheostatic fluid, glass tanks and a hot plate.

Background

Students will need to have an idea about density and molecular movement. During this time we will be looking at how heat is transferred from the core to the crust via convection. The students will be introduced to the idea of viscosity.

In-Class Activities

How Does the Crust Get Recycled?

In Class Activity:

* Begin the discussion with the idea that the materials on the Earth are basically constant and that scientists have found that rocks on the Earth vary in ages from brand new volcanic rock to rock that is 4 billion years old. Let them know that the rock in our area is approximately 400 million years old.

* Solicit ideas from the students about what they think causes this variation in ages?

* Bring up the idea that just like so much else in nature, the rocks also have a rock cycle. Remind them of the structure of the Earth with the core, mantle, and crust.

* Pose the question "How does the crust get recycled?" Give students a chance to right down their thoughts in their journals.

* At the front of the class have a set up with a hot plate, large glass container of water, and projector. Have the water heated on the hot plate. Have the projector about 3 feet from the container. Shine the beam of light through the projector so that the waters convection movement will be visible on a screen behind the container.

* Have the students describe what they observe in their journals. Remind them to give as much detail as possible.

* When they have had a chance to write, give them a chance to share their thinking with their groups and then have a class discussion for a couple of minutes to review the ideas of why the convection cycle works. Make sure to have them take note of the speed.

* Now tell students that different materials will be used. Repeat the procedure with corn syrup and then rheostatic fluid. Make sure that they have the different substances noted in their journals and that they describe in as much detail as possible. Have them notice that the rate of convection. After finishing have students share their ideas with their groups and then come together for a class discussion.

Day 2

* Have the 3 liquids in a clear cylinder. Drop a marble in each and watch how the marble fall through the liquid. Introduce the students to the idea of viscosity. Explain that solids can actually flow giving antique glass as an example. Also show the example of a ball of Silly Putty. Show how it can be solid and yet flow.

* Go back to the structure of the Earth with the very hot core, molten mantle and crust. Review what was observed with the fluids. Have students write their ideas down, making sure they back them up with evidence. Then ask the groups to come up with a theory about how the Earth's crust can be recycled.

* As a way to wrap up, remind students of the earthquake in Japan last year. Describe how it actually shifted Japan's placement making it move closer to California. Bring up the subduction zone. Then show them satellite images of the Mid-Atlantic Ridge. Point out that this is where some of the youngest rocks are found and that North America is moving incrementally away from Europe.

* Pull together the idea of the convection cycle in the mantle where cooler, denser crust is sub-ducted and hot, less dense magma forces its way up through ridges. This allows for recycling of the crust.

Materials –

Glass tanks

Water, corn syrup, rheostatic fluid

Hot plate

Journals

Satellite images of the Earth

Cylinders

Marbles

At Home Assignments

Standards

Massachusetts Earth Science 2,3,5
Massachusetts Physical Science 15,16

Informal formative assessment will be made on student participation in class, group, and entries in their journal

Videos - How the Earth Began
Bill Nye - 100 Greatest Discoveries