Plate Tectonics

• Continental Drift is the concept that continents were once joined and have since moved apart.
• The supercontinent was named Pangea.
• The Continental Drift theory lacked evidence and a mechanism for continental movement, leading to its initial rejection.

Evidences in Continental Drift

• Continents fit together like puzzle pieces.
• Mountain ranges across continents have identical rock structures.
• Fossils of similar species are found on different continents.
• Paleoclimate indicators suggest continents experienced different climates in the past.

Glacial Evidence

• Cirques are bowl-shaped depressions where glaciers once existed.
• Moraines mark the terminal boundary of a glacier or ice sheet.
• Till is sediment directly deposited by ice.
• Tillite is sedimentary rock formed from till.
• Glacial erratics are out-of-place rocks transported by ice.
• Global evidence, like tillites and erratics, suggests ancient ice presence.

Plate Tectonics

• Plate Tectonics involves the formation, movement, and destruction of lithospheric plates.
• Lithospheric plates comprise the Earth's crust and upper mantle, consisting of either continental or oceanic crust.

Evidences in Plate Tectonics

• Bathymetric data reveals mid-ocean ridges (MORs).
  • Bathymetric data refers to the shape of the ocean floor.
  • Mid-ocean ridges were discovered by Marie Tharp.
  • Depth is calculated using the formula: Depth = ½ (two-way travel time) (speed of sound in water).
• Seismic data indicates earthquake locations and strength.
  • Earthquakes generate seismic waves.
• Volcanic data reveals volcanic activity locations and historical eruptions.
• Plate boundaries, like mid-ocean ridges, are common locations for seismologic and volcanic activity.
• Plate boundaries are where plate edges meet and mainly where plate tectonic activity occurs.
• Magnetic minerals record their geographic (latitude) positions as they crystallize.
• The Earth's magnetic poles do not move significantly; continents move.
• The Earth's magnetic field flips or reverses from time to time.

Sea Floor Spreading

• Sea Floor Spreading explains oceanic crust production and movement.
• New crust is created at mid-ocean ridges.
• The oldest oceanic crust is farthest from the mid-ocean ridges.
• Sea Floor Spreading pushes the ocean crust away from the MORs.
• Subduction and recycling of oceanic crust is fast, making oceanic crust relatively young.
• Continental crust is much older than oceanic crust.
• Continental crust is produced by continental volcanism.
• Continental crust is destroyed slowly by weathering and erosion.
• Sea Floor Spreading creates oceanic crust, while continental volcanism creates continental crust.
• Subduction is when plate descends below another at convergent boundaries, leading to earthquakes/volcanic activity
• Continental crust does not subduct.

Summary of Plate Tectonic Evidence

• Bathymetric Data: Reveals mid-ocean ridges.
• Earthquake Data: Shows non-random earthquake locations.
• Volcanic Data: Co-occurs with earthquakes but is less common.
• Bathymetric Data, Earthquake Data & Volcanic Data: Outlines plates and plate boundaries.
• Magnetic Data: Supports continental movement, as compasses point in the wrong directions.
• Magnetic Data: Indicates oceanic crust production at mid-ocean ridges.
• The age of oceanic crust confirms oceanic crust is produced at MORs and moves away of them.

Plate Tectonics Process

• Formation:
  • Oceanic Crust: Sea floor spreading at mid-ocean ridges.
  • Continental Crust: Subduction leading to continental volcanism.
• Movement: Sea Floor Spreading through ridge push and slab pull.
• Destruction: Subduction (oceanic crust only).

Plate Composition Definitions

• Oceanic Crust: high density, thin, basalt/gabbro, can be subducted, not capable of flow, produced at mid-ocean ridges.
• Continental Crust: low density, think, granitic/rhyolitic, can’t be subducted, not capable of flow, produced by continental volcanism.
• Lithosphere: crust plus upper mantle = lithospheric plates, solid and not capable of flow.
• Asthenosphere: capable of flow, sits below the lithosphere.

Seismic Waves

• Seismic waves are caused by sudden breaking of rock or an explosion.
• P waves (primary waves) are the fastest seismic waves.
  • P waves compressional waves.
  • P waves move through solid rock and liquid.
• S waves (secondary waves) are slower than P waves.
  • S waves move rock particles up and down or side-to-side.
  • S waves can only move through solid rock, not liquids.
• Studying seismic waves reveals that the Earth's interior comprises solids, liquids, and semi-solids.

Plate Boundary Types

• Divergent: plates move away from each other.
  • Located at Mid-ocean ridges and rifting zones.
  • Produces oceanic crust (basalt/gabbro, thin, and high density).
• Convergent: plates move towards each other.
  • Produces continental crust (granitic/rhyolitic, thick, and low density).
  • Three types: ocean to ocean, ocean to continent, and continent to continent collision.
• Transform: plates move laterally past one another.
  • Connects mid-ocean ridges.
  • Example: San Andreas Fault.

Continental Margins

• Active Continental Margins: tectonically active edges along the continent-ocean boundary (e.g., western US).
• Passive Continental Margins: tectonically inactive edges along the continent-ocean boundary (e.g., eastern US).

Convergent Boundaries

• Ocean to ocean subduction results in the development of volcanic island arcs.
  • Example: Japan.
• Ocean to continental subduction leads to the development of a continental volcanic arc.
  • Example: Mt. St Helens.
• Continent to continent collision results in the development of non-volcanic mountain ranges.
  • Example: India and Asia colliding to form the Himalayas Mountains.

Transform Boundaries

• Connect other plate boundaries.
• The San Andreas transform fault connects the divergent boundary in the Gulf of California to the convergent boundary of the Northwestern US.