Plate Boundaries and Earth's Layers

Plate Boundaries

• Continental and oceanic crusts, and the lithosphere and asthenosphere are contrasted
• Mechanisms driving the movement of lithospheric plates are explained (convection, ridge push, slab pull)
• Three types of plate boundaries are listed, and their relative direction of plate motion is described.
• Real-world examples of each type of plate boundary are provided.
• Cross-sections of divergent and convergent plate boundaries are drawn.
• The methods scientists use to determine plate motion speed are explained, accompanied by a range of measured plate speeds.

Earth's Interior

• Earth's interior is hot
• Earth's structure is layered.
• The outer layer of Earth is fractured into moving pieces.

Earth's Layers

• Lithosphere = crust + uppermost mantle = a tectonic plate
• Asthenosphere = layer in the mantle (hot and weak solid)
• Continental crust is less dense than oceanic crust
• Continental crust is granitic
• Oceanic crust is basalt
• Oceanic crust density = 3.0 g/cm³
• Continental crust density = 2.7 g/cm³
• Mantle density = 3.3 g/cm³

Tectonic Plates

• A global map shows various tectonic plates.
• Divergent boundaries, convergent boundaries, and transform boundaries are labeled.

Plate Motion

• "Slab pull": As a plate sinks, gravity pulls the rest of the plate along.
• Convection: The movement of heat within Earth's mantle drives plate motion.

Plate Motion – Slab Pull

• An oceanic plate is subducted beneath a continental plate.
• Subduction is driven by the pulling force of the subducting plate.
• Viscous resistance may impede downward movement.

Plate Boundaries (Diagrams & Examples)

• Divergent plate boundaries, convergent plate boundaries, and transform boundaries are illustrated in diagrams.
• Examples of divergent plate boundaries: Mid-Atlantic Ridge, East African Rift Valley
• Examples of convergent plate boundaries: The Himalayas, Andes Mountains, volcanic island arcs
• Examples of transform plate boundaries: San Andreas Fault, some mid-ocean ridges.

Mid-Ocean Ridges

• AKA Spreading Centers.
• The most extensive chain of mountains on Earth.
• Magma fills fissures in the seafloor and solidifies forming new crust.
• Lava erupts onto the seafloor as it cools, except if spreading is too fast.

East Pacific Rise / Mid-Atlantic Ridge

• Fast-spreading (10s of cm/yr); gentle slopes (East Pacific Rise)
• Slow-spreading (few cm/yr); steep slopes (Mid-Atlantic Ridge)

Activity: Divergent Plate Boundary

• A diagram illustrates a divergent boundary showing plates moving apart. Key layers (crust, mantle, lithosphere, asthenosphere) are labeled, demonstrating new seafloor creation.

Activity: Convergent Plate Boundary

• Two convergent plate boundaries (ocean-continent and ocean-ocean) are illustrated in diagrams, showing layers are moving together. Key layers (crust, mantle, lithosphere, asthenosphere) are labeled.

Transform Fault Margins

• Transform boundaries are illustrated, labeled with key features such as the San Andreas Fault.

Plate Motion (Velocities)

• Plate velocities are on the order of centimeters to tens of centimeters per year. A world map displays different velocities.

Online Velocity Viewers

• Available online tools show plate velocities.

Future World (+50 Million Years)

• A map displays a model of tectonic plate motion based on plate velocity predictions showing future plate positions approximately 50 million years into the future.