Overview
This lecture explains mantle convection currents as the driving force of plate tectonics, covering heat transfer and how convection causes plate movement and boundary formation.
Plate Tectonic Theory Review
- Plate tectonic theory explains the movement of lithospheric plates, causing different types of plate boundaries.
- Plate boundaries can be convergent, divergent, or transform fault types.
- This theory supports Alfred Wegener’s continental drift theory.
- Plate tectonic theory explains why and how the plates move, which Wegener could not.
Heat Transfer and Convection Currents
- Heat is transferred by conduction, convection, and radiation.
- Convection occurs when heated fluids (like air, water, or magma) move; warm material rises, cool material sinks.
- Warm substances rise because heating decreases their density (molecules move apart).
- Cool substances become denser (molecules pack closer) and sink.
Mantle Convection & Plate Movement
- Magma near the Earth's outer core is hot and rises; as it cools farther from the core, it sinks.
- This cycle of rising and sinking magma forms convection currents in the mantle.
- Mantle convection causes lithospheric plates to move, similar to eggshells floating on moving batter.
- Convection currents can move in clockwise or counterclockwise directions.
Plate Boundaries and Convection
- Opposing directions of convection cells lead to different boundary types.
- Convergent boundaries: neighboring convection cells move plates toward each other.
- Divergent boundaries: convection cells move plates away from each other.
Key Terms & Definitions
- Plate Tectonic Theory — the concept that the Earth's lithosphere is divided into moving plates.
- Convection Current — movement in fluids (like magma) where heated material rises and cooled material sinks, forming a cycle.
- Density — how closely packed molecules are in a substance; affects whether it rises or sinks.
- Lithospheric Plate — rigid section of Earth's outer shell.
- Asthenosphere — upper part of the mantle beneath the lithosphere.
Action Items / Next Steps
- Create a pamphlet about mantle convection currents; follow procedures and rubrics on module pages 15-16.
- Complete the three-question assessment on an intermediate pad.
- Contact your teacher with any questions.