Overview
This lecture covers convection currents in Earth's mantle, their impact on plate tectonics (ridge push and slab pull), and the resulting geological processes and formations, including seafloor spreading and subduction.
Convection Currents in the Mantle
- Convection currents are the circular movement of magma in the mantle due to heat from the core.
- Warm magma rises in the mantle's center, while cooler magma sinks at the sides.
- Convection currents occur within the mantle and are driven by heat from the core.
Plate Tectonics: Ridge Push and Slab Pull
- Ridge push occurs at divergent boundaries where two oceanic crusts move apart.
- Slab pull happens at convergent boundaries where denser oceanic crust subducts beneath continental crust.
- Oceanic-oceanic divergence forms mid-ocean ridges due to ridge push.
- Continental-oceanic convergence forms trenches due to slab pull (subduction).
Plate Movements and Their Consequences
- Seafloor spreads at approximately 3 centimeters per year.
- Ridge push and slab pull are responsible for plate movements and geological formations like mountains, volcanoes, and trenches.
- Practical parallels: conveyor belts, anchors with chains, and escalators can model ridge push and slab pull.
The Role of the Core’s Heat
- If Earth’s core cooled, convection currents, ridge push, and slab pull would stop.
- Without plate movement, geological processes and landform creation (mountains, volcanoes, etc.) would cease.
- The continents would remain joined as a supercontinent; Earth would be geologically "dead."
Earth’s Size Maintenance Despite Seafloor Spreading
- As new crust forms at mid-ocean ridges, old crust is subducted into the mantle.
- The subducted crust sinks to the mantle, melts into magma, is expelled by volcanoes as lava, and cools into new rock.
- This cycle ensures Earth’s size remains constant.
Key Terms & Definitions
- Convection Currents — Circular movement of magma in the mantle caused by core heat.
- Ridge Push — Plate movement at oceanic-oceanic divergent boundaries, forming mid-ocean ridges.
- Slab Pull — Subduction of oceanic crust at convergent boundaries, forming trenches.
- Seafloor Spreading — Process by which new oceanic crust is created at mid-ocean ridges and moves away.
- Subduction — Process where one tectonic plate sinks beneath another into the mantle.
Action Items / Next Steps
- Watch the uploaded tutorial video on assembling the improvised seafloor spreading model.
- Prepare materials (show box, seafloor stripe printouts) for tomorrow’s performance task on seafloor spreading.