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Plate Tectonics
Plate tectonics is the unifying theory of geology andrevolutionized geology
cornerstone of Earth-system approach; explainsconnections between seemingly unrelated geologicphenomena
permits Earth’s history to be viewed as series ofinterrelated events.
explains how plate interactions determine locations ofcontinents, mountain ranges, and ocean basins, and thusaffect atmospheric and oceanic circulation patterns thatcontrol climate
explains influence of plate movement on distribution,evolution, and extinction of plants and animals.
Why Study Plate Tectonics?
Geographic distribution of geologic hazards such asearthquakes and volcanic eruptions controlled by platetectonics - Many global and regional political and economicproblems stem from uneven distribution of geologicresources such asoil and metal ores. - Formation ofgeologic resourcesis controlled byplate movement. Harry K. Brown Park, Kilaueahttp://hvo.wr.usgs.gov
Early theories
With the discovery of radioactivity andrecognition that this generated heat it wassuggested that the Earth was expanding
This could account for some features butdid not explain the mountain belts
In the 1960’s we finally came around tothe idea of plate tectonics but the basis forthe theory came much earlier
Edward Suess (1885), anAustrian geologist, proposedIndia, Africa, Australia, and SouthAmerica were once connected byland bridges (referred to thissouthern hemisphere landmassas Gondwana).
Origins of a theory
Chernicoff and Whitney (2002)
Origins of a theory Alexander du Toit (1937), South African geologist, developed Wegener’s ideasand introduced large body of geologic evidence to support continental drift (andreferred to north landmass of Pangaea as Laurasia).
Plummer et al. (2001)
Continental drift
Chernicoff and Whitney (2002)
Wicander and Monroe (2002)
Continental Fit
Best fit among continents resultswhen they are matched along theircontinental slopes where erosionhas not significantly reconfiguredtheir shape.
Here the continents are shownjoined along their continentalslopes to form the super-continent Pangaea, originallyproposed by Wegener.
Continental fit
Murck and Skinner (2002) Murck and Skinner (2002)
Wicander andMonroe (2002)
Glacial Features
The distribution of glacialdeposits (till) and striations(scratches) of similar ageindicate that Gondwanacontinents were once joinedtogether and situated in thevicinity of the South Pole,where a vast continentalglacier covered large areas ofall five continents.
Glacial Features
Arrows indicate direction of ice flow
Montgomery (2001)
Montgomery (2001)
Fossil distribution
Beginnings of consensus
Wegener and du Toit cited the bodies of evidence listedabove to support their theory of continental drift, but aslate as the 1950s most geologists did not accept theidea of moving continents. - The lack of a viable mechanism was the main reasonthat the theory did not gain wide acceptance for 40years - By the 1960s, studies of the paleomagnetism of rockshad yielded strong evidence for continental drift.
The Earth’s Magnetic Field
Earth’s magnetic field consistsof invisible lines of force akin tothose surrounding a barmagnet.
Remnant magnetism in rocksrecords Earth’s ancientmagnetic fields and the locationof Earth’s ancient magneticpoles at the time the rocksformed and is referred to aspaleomagnetism. Wicander and Monroe (2002)
Inclination of the lines of force comprising Earth’s magneticfield varies with distance from the equator. At the equator,they parallel Earth’s surface, but their inclination increaseswith distance from the equator until at the magnetic polesthey are perpendicular to Earth’s surface.^ Wicander andMonroe (2002)
The Earth’s Magnetic Field
