Convection Currents
This teacher demonstration helps students understand the motion of convection currents in the Earth's mantle.

You will need:
Deep, clear glass heat-proof dish
Blocks
Votive candle
Match
Cooking oil
Food coloring gel
Small container with lid
Chart paper
Markers

Procedure
1. Fill the glass dish with oil. Tell students this represents the Earth's mantle, although the mantle is not the same consistency as oil.
2. Prop each end of the dish up with blocks, then place the candle under the dish. Light the candle. Ask: What might this heat source represent? (the heat of the core)
3. After allowing the oil to heat for several minutes, pose the question: If this oil is moving, how can we tell? Explain that we can use food dye to track the movement of the oil. Squeeze some food coloring gel into the small container. Add oil, close the lid, and shake vigorously to break the dye into smaller drops. Slowly pour the mixture into the oil above the heat source.
4. Allow small groups of students to closely observe the path of the oil by watching the bits of dye moving. Each group should diagram the lab materials and draw arrows to show the motion.
5. Once each group has attempted a drawing, discuss the reasons for this motion. Heat expands the substance closest to it, causing it to rise. When it reaches the surface, it begins to cool and condense, moving away from the heat source, then falling back to the bottom. Similar movement in the Earth's mantle causes much of the "action" on the crust.