My Science Box

Summary
Students take what they know about earthquake, volcano and mid-ocean ridge distributions (The Big One and Plate Patterns) and put it together with what they know about convection in the Earth’s mantle (Journey Through Earth and Convection in a Pan). They revisit what they know about how earthquakes are created, by the sudden release of energy as plates collide or rub together (but not so much when they split apart). They look for patterns in their world maps, observing that mid-ocean ridges and dense earthquake/volcano zones tend to lie on the opposite side of plates. With this information, they can infer the direction that the plates are moving. Next students build a model illustrating seafloor spreading and discuss the magnetic and seafloor age data that support this model. Finally, students codify the different types of plate boundaries, describing the various features and characteristics of each.

Sources
The activity elaborates upon one of the Exploratorium’s science snacks “Pie Pan Convection”.

The hot air balloon demonstration was taken from a lesson by Gregory Vogt, edited by Roger Storm of the NASA Glenn Research Center. See their lesson plan for detailed information, diagrams and tips.

Assessment

1. Collect the students’ handouts and drawings.
2. In teams, have students predict what would happen in the following scenarios.
   • You put a pot of cool water on the stove. You turn on the flame below the pot. The water at the bottom of the pot nearest the flame begins to get hot. Will convection currents be created? If so, diagram them, showing how the convection currents would move through the water. If not, explain why not.
   • You have a pot of cool water sitting on the table. You turn on a heat lamp above the pot. The water at the top of the pot nearest the heat lamp begins to get hot. Will convection currents be created? If so, diagram them, showing how the convection currents would move through the water. If not, explain why not.
   • You close all the windows and doors of the classroom. You set a portable camping stove on the floor in the middle of the room and turn the burner on. The air near the burner gets hot. Will convection currents be created? If so, diagram them, showing how the convection currents would move through the air in the room. If not, explain why not.
   • You have a rectangular pan full of water. You balance the pan on a pedestal. Under one end of the pan you light a candle. The water near that end gets hot. Under the other end of the pan you place a large pot of ice water. The water near that end gets cold. Will convection currents be created? If so, diagram them, showing how the convection currents would move through the water. If not, explain why not.
   • Think about the Pacific Ocean. The water near the equator is warmed by the sun. The water near the North and South Poles gets less direct sunlight and is very very cold. Will convection currents be created? If so, diagram them, showing how the convection currents would move through the water. If not, explain why not. (Hint, look at your answer to the previous question.)

Lesson Plan
Hot air balloon demo

1. Start class by asking for 4 volunteers.
2. Have 1 volunteer hold the top of the pre-tested bag with paper clips attached and 2 others to hold the bottom edges open.
3. Have the third volunteer turn on the blow dryer to the lowest setting and hold it under the opening. Make sure the blow dryer isn’t too close to the opening that it melts the bag or overheats your volunteers hands.
4. As the bag fills, have the other students predict what will happen.
5. When the bag is full, have the blow dryer volunteer turn the dryer off.
6. On the count of three, have the other 3 volunteers let go and watch the balloon fly.
7. When the bag finally comes back down, discuss what happened. Some questions to consider include:
   • Why did the bag fly? What powered it?
   • How is the hot air balloon the same or different than a helium balloon? Was helium used?
   • What would happen if we used a regular fan blowing room temperature air into the bag? Why?
   • What would happen if we let an air conditioning vent fill the bag? Why?
   • Where is it hottest above a fire – directly above the flames or an equal distance to the sides of the flame? Why?
   • What happens to the steam above a pot of boiling water? Where does it go? Why?
   • If hot air rises, what do you think will happen to cold air?
   • Do you think this happens in a liquid? Do you think hot water will rise among cooler water? How about in a solid?

Getting Ready

Test the hot air balloon demo

1. Use cellophane tape to seal the top seam and any holes in the dry cleaner bag. Use as little tape as possible.
2. Clip 3-4 paper clips around the bottom edge of the bag, as evenly distributed as possible. This will keep the bag upright and stable as it takes flight.
3. Hold the bag at the top. Get helpers or use 2 chairs to keep the bottom edges open.
4. Turn the blow dryer on at the lowest setting and hold it near the bottom of the bag (but not so close that the bag begins to melt). Allow the hot air to inflate the bag.
5. When the bag is fully inflated, let go of it to test its buoyancy. If it lifts off, let it go. If it doesn’t, continue filling with the blow dryer for a little longer.
6. Watch its flight, taking note of how stable it is in the air. When it lands again, adjust the paper clips to make it more stable. If it tilts one way, move them to different locations. If it flips over completely, add more paper clips. If it doesn't fly at all, remove some clips.
   

Teacher Background
The earth has several major layers – a hot metallic core, a less hot liquid mantle, and the solid lithosphere and crust on top (see background section of Journey Through Earth for more information). The hot metallic core causes the mantle immediately above to heat up. As the liquid rock in the mantle heats up, it rises because a heated liquid (or gas) expands and becomes less dense than the cooler liquid (or gas) nearby. When this hot liquid reaches the top of the mantle layer, it gets pushed aside by more hot mantle rising below it, spreading out under the solid lithosphere above like a cloud of steam hitting the ceiling of the kitchen. As it spreads out, it cools. Cool liquids (and gases) shrink in volume and are more dense than the warmer liquids (or gases) nearby. Therefore, the cooled mantle sinks to the bottom of the mantle layer where it gets heated by the core and begins the cycle anew.

Time
10 min demo and introduction
30-40 min investigation
10-15 min discussion

Grouping
Groups of 4-6 students

Materials
For the demo, the teacher needs:

• One dry cleaner bag
• Cellophane tape
• 3-4 paper clips
• Blow dryer (hand held hair dryer)

Each group of students needs:

Summary
What drives the motion of the Earth’s tectonic plates? Partly, it is convection, the process by which heat energy is transferred by currents in a liquid or gas. Convection currents within the mantle carry tectonic plates along with the slowly moving mantle like giant rafts carried along by a current in a river. To help students understand this idea, soapy water in a pie pan is heated from below and convections currents can be observed forming and moving in the soapy water. Several prelude demonstrations help students recognize that hot things rise and cold things sink.

Standards
Grade 6
Plate Tectonics and Earth's Structure
1. Plate tectonics accounts for important features of Earth's surface and major geologic events. As a basis for understanding this concept:
b. Students know Earth is composed of several layers: a cold, brittle lithosphere; a hot, convecting mantle; and a dense, metallic core.
c. Students know lithospheric plates the size of continents and oceans move at rates of centimeters per year in response to movements in the mantle.

Lesson Plan
Download a detailed lesson plan for this activity from Eric Muller’s website.