Plate tectonics shapes Earth's surface, driving the movement of continents and formation of oceans. This theory explains how Earth's crust is divided into plates that slide and collide, causing earthquakes, volcanoes, and .
Evidence for plate tectonics includes the fit of continents, matching rock formations, and . Modern tech like GPS confirms plate motion, showing how our planet's surface constantly changes over millions of years.
Plate Tectonics Theory and Evidence
Foundations and Historical Development
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Plate tectonics unifying theory in geology explains large-scale motions of Earth's divided into several plates moving relative to one another
Evolved from concept proposed by in 1912 suggested continents moved across Earth's surface
Continental drift initially met with skepticism due to lack of mechanism explaining movement
Supporting Evidence
Fit of continents particularly noticeable between South America and Africa
Matching rock formations and fossils across continents (Glossopteris flora found in South America, Africa, India, and Antarctica)
study of Earth's magnetic field preserved in rocks reveals past positions of continents
Seafloor spreading process of creating new oceanic crust at
Distribution of earthquakes and volcanoes concentrated along plate boundaries
Modern Confirmations
Discovery of mid-ocean ridges and magnetic striping patterns on ocean floor provided crucial evidence for seafloor spreading
Magnetic striping results from periodic reversals of Earth's magnetic field recorded in newly formed oceanic crust
Modern technologies (GPS and satellite measurements) provide direct evidence of plate motion
GPS measurements confirm plates move at rates of a few centimeters per year
Plate Boundaries and Features
Divergent Boundaries
Occur where plates move apart creating new crust
Associated with mid-ocean ridges underwater mountain ranges formed by upwelling magma
form where divergent boundaries occur on continents ()
Characterized by shallow earthquakes and
Examples include Mid-Atlantic Ridge and East Pacific Rise
Convergent Boundaries
Involve plates moving towards each other resulting in either subduction or collision
where one plate sinks beneath another characterized by:
()
()
Formation of accretionary wedges sediment scraped off subducting plate
Collision zones where two continental plates meet result in extensive mountain building:
formed by collision of Indian and Eurasian plates
Alps resulted from African and Eurasian plate collision
Transform Boundaries
Plates slide past each other horizontally creating strike-slip faults
Associated with shallow earthquakes but typically no volcanism
in California prime example of
in New Zealand another significant transform boundary
Complex Interactions
Triple junctions regions where three plate boundaries meet
Can result in unique geologic features (Afar Triple Junction)
Some areas experience diffuse plate boundaries broad zones of deformation (Basin and Range Province in western North America)
Mechanisms of Plate Motion
Primary Driving Forces
in Earth's mantle caused by heat from radioactive decay and residual heat from Earth's formation
gravitational force exerted by subducting plates considered dominant mechanism for plate motion
force exerted by elevation difference between mid-ocean ridges and older cooler oceanic crust
rising columns of hot material from deep mantle influence plate motion
Secondary Factors
Tidal forces from Moon and Sun may play minor role in plate motion
Earth's rotation (Coriolis effect) influences direction of plate movement
Gravitational potential energy differences due to topography contribute to plate motion
Resulting Geologic Processes
Crustal deformation folding and faulting of rocks
alteration of rocks due to heat and pressure
formation and movement of magma within Earth's crust
Rock cycle continuous transformation of rocks between igneous sedimentary and metamorphic types
Wilson Cycle
Formation and destruction of ocean basins over hundreds of millions of years
Stages include:
Rifting of continents
Seafloor spreading
Subduction of oceanic crust
Continental collision
Eventual rifting and cycle restart
Formation of Earthquakes, Volcanoes, and Mountains
Earthquake Distribution and Mechanisms
Primarily occur along plate boundaries due to sudden release of accumulated stress in rocks
Majority occur in subduction zones particularly around Pacific Ring of Fire
Large magnitude events common in subduction zones due to extensive contact area between plates
Intraplate earthquakes occur within stable continental interiors (New Madrid Seismic Zone)
Earthquake depth varies by tectonic setting:
Shallow at divergent and transform boundaries
Deep at subduction zones (up to 700 km)
Volcanic Formation and Distribution
Form through various tectonic processes:
Subduction creating volcanic arcs (Cascade Range)
Divergent boundaries producing shield volcanoes at mid-ocean ridges (Mauna Loa)