[Q2] EarthSci - Plate Tectonics

• Continental Drift + Sea Floor Spreading = Plate Tectonics
• Alfred Wegener (1596) - introduced the continental drift theory
• Pangaea - all of the continents were once together as one single landmass, which means "all land"; broke about 20 million years ago
• Continental Drift Theory - continents were once joined together and have since drifted apart
• Wegener found 4 major pieces of evidence to support his idea of continental drift:

  • Shape
  • Fossils
  • Climates
  • Rocks
• Shape Clues - continents fit together like puzzle pieces
• Fossil Clues - identical index fossils were found on separate continents
• Climate Clues - evidence of major climate changes
• Rock Clues - rock and rock structures on different continents are the same where the land was once joined
• Seafloor Spreading - geologic process where there is a gradual addition of new oceanic crust in the ocean floor through a volcanic activity while moving the older rocks away from the mid-oceanic ridge; helps explain continental drift in the theory of plate tectonics
• The mid-ocean ridge is where the seafloor spreading occurs, in which tectonic plates, large slabs of Earth's lithosphere, split apart from each other. This is the region where new oceanic crust is created.
• The seafloor spreading hypothesis was proposed by the American geophysicist Harry H. Hess in 1960.
• The continents bordering the Atlantic Ocean, for example, are believed to be moving away from the Mid-Atlantic Ridge at a rate of 1–2 cm (0.4–0.8 inch) per year, thus increasing the breadth of the ocean basin by twice that amount.
• Oceanic Crust - composed of rocks that move away from the ridge as new crust is being formed
• Seafloor spreading leads to the renewal of the ocean floor in every 200 million years, a period of time for building a mid-ocean ridge, moving away across the ocean and subduction into a trench.
• Plate tectonics unifies the principles of:

  • Continental Drift
  • Seafloor Expansion
  • Magnetic Field Reversal
  • Other Geological and Geophysical Findings
• Tectonic Plates - the lithosphere is not a single sheet, but consists of numerous irregularly formed parts; oceanic or continental crust or both
• Plates - number of rigid but moving pieces of the Earth's crust
• Fault Lines - where plates may rub against each other or move apart from one another
• Major Plates in the World

  • African
  • Eurasian
  • South American
  • Pacific
  • Antarctic
  • Indian-Australian
  • North American
• Minor Plates in the World

  • Juan de Fuca
  • Arabian
  • Caribbean
  • Cocos
  • Philippine
  • Nazca
  • Scotia
• Three Types of Plates Boundaries

  • Divergent
  • Convergent
  • Transform
• Divergent Boundary - when two tectonic plates move away from each other
• Rift Zones - areas where continents begin to spread, break apart, and expand over time
• East African Rifts System - where the eastern part of Africa breaks apart from the rest of the continent
• Convergent Boundary - where two plates pass towards each other and the plates are forced together; this method called subduction, occurs within a boundary called a subduction zone
• Volcanic Arc - a chain of volcanoes on the edge of the overhanging plate; result of subduction
• Mariana Trench - deep-sea trench; lowest portion of the Planet
• Mountain Belt Collision - responsible for the creation of the large chains of mountains that we know today
• Himalayan Mountain Range - where Mount Everest is situated
• Transform Plate Boundary - where two plates slide over each other, reminiscent of a strike-slip fault; often referred to as major strike-slip faults or transformation faults
• San Andreas Fault - links the ridge at the Southern California to the ridge offshore of Northern California