Geology Quiz: Continental Drift and Plate Tectonics

Continental Drift and Pangaea

• Pangaea was the supercontinent when all Earth's landmasses were joined.
• Evidence for Pangaea includes similar fossils on now-separated continents and similar rock formations and mountain ranges.
• Coal deposits in Antarctica suggest a warmer climate in the past, consistent with Pangaea's placement.

Earth's Magnetic Field

• Earth acts as a magnet due to moving molten iron in its outer core, producing a magnetic field.
• A compass uses a magnetized needle aligned with Earth's magnetic field. Earth's geographic and magnetic poles are not exactly aligned.
• Reverse polarity occurs when Earth's magnetic poles switch. This affects compass directions.

Seafloor Spreading

• Seafloor spreading involves magma rising at mid-ocean ridges, forming new crust.
• The new crust pushes older crust outward.
• Older crust eventually sinks back into the mantle at subduction zones.

Plate Tectonics

• Divergent boundaries: Plates move apart, forming new crust (mid-ocean ridges).
• Convergent boundaries: Plates collide, leading to subduction or mountain building.
• Transform boundaries: Plates slide past each other horizontally.

Convection Currents

• Convection currents in the mantle result from heated magma rising and cooler magma sinking.
• This cycle drives the movement of tectonic plates.

Forces Driving Plate Movement

• Ridge push: Elevated oceanic crust pushes plates apart.
• Slab pull: Sinking dense plate edges pull the rest of the plate.

Volcanic Features

• Caldera: A large, bowl-shaped depression at a volcano summit formed by collapse after magma evacuation.
• Volcano Types:
  • Shield volcanoes: Broad, gentle slopes formed by fluid lava flows.
  • Composite volcanoes: Steep, mountain-like structures from alternating lava and pyroclastic eruptions.
  • Cinder cone volcanoes: Small, steep cones formed by ejected fragments.

Magma Properties

• Magma viscosity (thickness) is determined by silica content (high silica = thick magma).
• High viscosity magma leads to explosive eruptions and composite volcanoes.
• Low viscosity magma leads to quiet eruptions and shield volcanoes.

Intrusive Igneous Features

• Dike: A vertical intrusion cutting across rock layers.
• Sill: A horizontal intrusion between rock layers.
• Laccolith: A dome-shaped intrusion pushing rock layers upward.
• Batholith: A massive underground igneous rock body greater than 100 km².

Stress on Rocks

• Compression: Squeezes rocks, common at convergent boundaries.
• Tension: Pulls rocks apart, common at divergent boundaries.
• Shear: Moves rocks past horizontally, frequent at transform boundaries.

Rock Deformation

• Elastic deformation: Temporary change, reversible shape change from force, the object returns to its original shape when stress is removed
• Plastic deformation: Permanent change in shape or size from force, the object does not return to its original shape when stress is removed.

Faults

• Reverse fault: Hanging wall moves up relative to the footwall (compression).
• Normal fault: Hanging wall moves down relative to the footwall (tension).
• Strike-slip fault: Rocks slide horizontally past each other (shear).

Earthquakes

• Seismic waves: Energy waves travelling through Earth's layers from an earthquake.

• Types of seismic waves:

  • P-Waves: Compression waves.
  • S-Waves: Shear waves.
  • Surface waves: Slowest, cause most surface damage.

• Focus: Point within the Earth where an earthquake originates.

• Epicenter: Point on the surface directly above the focus.

Seismometers

• Seismometers detect and measure seismic waves using a suspended mass.

Earthquake Measurement

• Magnitude scale: Moment magnitude measures total energy released.
• Intensity scale: Mercalli scale rates earthquake effects on humans, structures.