** The theory of global dynamics in which the lithosphere is believed to broken
into individual pieces or plates that move in response to convection in the upper mantle.
History of the theory:
*** Alfred Wegener, a German meteorologist, gave it serious consideration in 1915, and
was the first to suggest that continents were moving, and to supply some evidence for it.
His Theory of Continental Drift took awhile to be fully accepted by the established
* evidence: similarities of fossils, climate records, & geologic record between distant
countries, esp. South America &Africa
EX: * the land dwelling, mammal-like reptile Lystrosaurus, whose fossils have been
found in SouthAmerica, Africa, Antarctica andAsia
* mountain belts of similar age, rock sequence, fossils & structural style appear on both
sides of the NorthernAtlantic (Appalachians & those of Ireland, Scotland & Norway)
* Wegener proposed that one landmass existed about 200-225 MYBP (Triassic-Jurassic
Periods) and called it Pangea. This began to split over the next 10-20 million years.
* by about 135 MYBP (early Cretaceous) it had broken into 2 large pieces, Laurasia
(basically present-day North America, Europe, &Asia) & Gondwana (the southern
* 1940-1960's,Atlantic Ocean floor mapping enhanced our knowledgeof tectonic
* 1960's,Harry H. Hess & Robert S. Dietz proposed a theory of Sea-Floor Spreading
* Sea-floor spreading: the movement of crustal material by the upwelling of magma
along a system of mid-oceanic ridges
KNOW THATTHE OLDEST ROCK IS 4 BILLION YEARS OLD
* the upwelling pushes the crust away from the ridge *
oldest crust is furthest from the ridge, newer crust closest * oldest sea
floor dated so far formed ~200 MYBP * idea of magnetic
reversals or paleomagnetism enhanced this theory
* discovery of magnetic reversals, or paleomagnetism, tested and proved the theory of sea-floor spreading. Paleomagnetism refers to the magnetic alignment of charged
particles (esp. Iron material) in the rock which exhibit a symmetrical pattern as you move
away from the mid-oceanic ridge. The polarity, the orientation of positive(+) &
negative(-) to the Poles of the Earth, changes as you move away from the mid-oceanic
ridge because the rock cools/forms at different times.
* By 1980's the theory ofPlate Tectonics had been developed, which combined the
ideas of sea-floor spreading, continental drift, paleomagnetism and other ideas.
Plate Tectonics: is the theory covering crustal movements and the foundation of crustal
* Tectonic processes: upwelling of magma, plate movement, subduction of crust,
folding, faulting, warping, fracturing, earthquakes, volcanic activity
Distribution of Plates:
* currently at least 20 - 22 plates are recognized, with 8 - 10 major plates
* major plates: Pacific, N.American, S.American, Eurasian, African,
Australian, Indian, Antarctic, Nazca
* Several smaller plates: Cocos, Caribbean, Arabian,