Plate tectonics and the ocean floor
Subduction zones
(beyond Mid-Ocean Ridge) place where two lithospheric plates come together, one riding over the other. oceanic trench site of crust destruction Subduction can generate deep ocean trenches
polar wandering
Apparent polar wandering Location of North Pole changed over time - plates shifting
Plate Tectonics
Alfred Wegener first proposed in 1912 Called it "Continental Drift"
Continental Drift
Continental drift - The idea that the continents slowly moved over Earth's surface.
Types of Boundaries
Convergent Boundary - Converge - come together Divergent Boundary - divide - go apart Transform Boundary - slide back and forth
Evidence
Distribution of organisms Same fossils found on continents that today are widely separated Modern organisms with similar ancestries
paleomagnetism
Earth's magnetic field and paleomagnetism (study of Earth's ancient magnetic field) Earth has magnetic polarity North and South polarities Magnetic polarity recorded in igneous rocks Magnetite in basalt
Magnetic Polarity Reversals
Earth's magnetic polarity reverses periodically - field direction reverses Recorded in ancient igneous rocks
Sea Floor Spreading
Harry Hess World War II submarine captain and geologist Depth recordings show sea floor features History of Ocean Basins Seafloor spreading Mantle convection cells as driving mechanism.Mid-ocean ridge - spreading center
Heat Flow
Heat flow - heat from Earth's interior released to surface Very high at mid-ocean ridges Low at subduction zones
Convection Currents in Earth
Heat from the core and the mantle causes convection currents in the mantle. Temperature increase - rise Temperature decrease - sink
Convection Current
Hot magma in the Earth moves toward the surface, cools, then sinks again in a circular pattern. Creates convection currents (circulate) beneath the plates that cause the plates to move.
Plate Tectonics Theory
Lithosphere - tectonic plates that float on ductile asthenosphere Large-scale geologic features occur at plate boundaries. = Volcanos, earthquakes, tsunamis
Earthquakes as Evidence
Most large earthquakes occur at subduction zones. Earthquake activity mirrors tectonic plate boundaries.
magnetic field
New evidence from World War II Sea floor studies with sonar New technology enabled study of Earth's magnetic field
Types of Spreading Centers
Oceanic rise Fast-spreading Gentle slopes East Pacific Oceanic ridge Slow-spreading Steep slopes Mid-Atlantic Ultra-slow Deep rift valley Widely scattered volcanoes Arctic and southwest India
Types of Convergent Boundaries
Oceanic-Continental Convergence Ocean plate is subducted Continental arcs generated Explosive andesitic volcanic eruptions
Divergent Boundary Features
Plates move apart Mid-ocean ridge Rift valley New ocean floor created Shallow focus earthquakes Intensity measured with seismic moment magnitude
Convergent Boundaries
Plates move toward each other Earthquakes, forms mountain ranges Ex) Himalayan Mountains
Convergent Boundary Features
Plates move toward each other Oceanic crust destroyed Ocean trench Volcanic arc Deep focus earthquakes Great forces involved Mineral structure changes associated
Sir Edward Bullard
Puzzle-like fit corroborated in 1960s Sir Edward Bullard used computer models to fit continents.Matching sequences of rocks and mountain chains Similar rock types, ages, and structures on different continents
Scientists theorize
Scientists theorize that a super-continent known as Pangaea existed. This super-continent was made up of all the continents on Earth.
What is Plate Tectonics
The Earth's crust and upper mantle are broken into sections called plates Plates move around on top of the mantle like rafts Why? because their density (2.7-3.0) is less than the mantle (3.3-5.7)
Pangea
The break up of Pangea
Evidence for Continental Drift
Wegener proposed Pangaea - one large continent existed millions years ago Panthalassa - one large ocean Noted puzzle-like fit of modern continents