PLATE TECTONICS

• Before the plate tectonics, there was no coherent theory to explain Earth's structure and processes.
• Neptunism - all rocks come from deposition from a primordial ocean
• Plutonism - all rocks are formed by igneous processes (crystallization from magma)
• Continental drift theory - proposed by Alfred Wegener in a series of paper from 1910 to 1928
• The Origin of Continents - book by Alfred Wegener explaining the continental drift theory
• Continental drift theory - suggests that all continents were joined into a single large landmass supercontinent called Pangaea surrounded by an ocean called Panthalassa around 280 mya (late Paleozoic)
• Pangaea - "all land"
• Panthalassa - all sea
• Laurasia - North America, Asia, Europe, and Greenland.
• Gondwana - Africa, South America, India, Antarctica, and Australia
• Tethys sea - separated the northern Laurasia and southern Gondwanaland
• Continental drift theory 4 EVIDENCES

  1. Fit of the continents
  2. Fossil evidence
  3. Similar lithologies (rock types) across continents
  4. Paleoclimate
• Fit of the continents - coastlines and continental shelves fit perfectly especially the continents of South America and Africa
• Glossopteris - found in 5 continents (Gondwanaland continents): Africa, South America, India, Australia, Antarctica
• Glossopteris - immobile and grows in certain temperature and environment
• Fossil evidence

  1. Cynognathus - land therapsids
  2. Mesosaurus - freshwater alligator-like reptile

  Both are land-dominant animals that are incapable of migrating between oceans.
• Lystrosaurus - land-dwelling herbivore found in Africa, India, and Antarctica
• Lystrosaurus - its build would have the swimming capability to traverse oceans
• Evidence 3: Similar lithologies across continents

  1. Appalachian mountains (North America) and Caledonian Mountains (Europe)
  2. Cape Fold Belt (Africa) and igneous formation (South America)
• Evidence 4: Paleoclimate

  1. Glacial deposits found in warm climate continents (South America, India, South Africa, Australia, Antarctica)
  2. Tropical plants and coal deposits found in frozen regions (Canada, Arctic, Europe, and Asia)
• Seafloor spreading - proposed by Harry Hammond Hess in 1960 (published in History of Ocean Basins in 1962)
• Seafloor spreading - coined by Robert Dietz in 1961
• Seafloor spreading - suggests that seafloor moves and carries the crust with it as it spreads from a central rift axis (at the oceanic ridge)
• Oceanic ridges - long sinuous ridges that occupy the middle of the Atlantic Ocean and the eastern part of the Pacific Ocean
• Oceanic trenches - deep depressions along the margins of continents
• Seafloor spreading

  1. Oceanographers were equipped with new marine tools and funding for oceanographic exploration
  2. Discovery of oceanic ridge system
  3. Oceanic crust near these ridge systems were found to be younger
• Paleomagnetism - remnant magnetism, record of Earth's magnetic field through time
• Geodynamo - creates the magnetic field of the Earth
• Magnetite - iron bearing minerals
• Curie Temperature - temperature where magnetic minerals change magnetic behavior
• The magnetic north is usually located around 11.5 degrees away from the geographic north (true north) and is the direction where our compasses point to.
• Apparent polar wandering - a moving continent will retain a record of changing paleomagnetic directions through time that reflect the changing orientations and distances to the pole (which is held fixed)
• Apparent polar wander path - APWP, resulting path of observed pole positions
• Paleomagnetism - It was discovered that rocks with increasing age point to pole locations increasingly far from present magnetic pole positions.
• Paleomagnetism

  1. Earth has more than one magnetic pole at various times

  2. The continents moved relative to each other over time.
• Geomagnetic reversal - shifting of the pole's polarity over time (the north magnetic pole becomes the south magnetic pole and vice versa)
• Geomagnetic reversals - happens every 300,000 years, with the last reversals being 770,000 years ago
• Paleomagnetism - discovered by Achilles Delesse
• Geomagnetic reversals - new crust created in oceanic ridges records this reversal in polarities throughout geologic time
• Plate tectonics - brought together in 1968 based on evidences presented from continental drift theory, seafloor spreading, and paleomagnetic evidences