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Layers of the Earth
  • Earth: built by distinct layers: inner core, outer core, mantle, crust; the crust is the thinnest layer
  • Lithosphere: outer rigid „shell“ of Earth
  • Asthenosphere: warmer, plastic (flowing) underlying layer of mantle
  • Continents are „floating“ on plastic layers: Alfred Wegener‘s theory of continental drift (1915), proven in the late 1960‘s by deep-sea sediment cores
  • Tectonic plates: Earth‘s surface is composed of several drifting plates, comprising both continents and sea floor
  • Heat from Earth‘s interior causes convection cells within magma
  • Mid-ocean ridges: hot magma breaks through lithosphere and „pushes“ lithosphere to both sides; plates move away from ridges
  • Deep-sea trenches are subduction zones: two plates collide due to opposite drift directions, one plate dives underneath the other; the subducted plate material is melted into the magma again
  • Ring of fire: plate borders can be seen by plotting earth quakes or vulcanic activity, which occur at plate boundaries
  • Origin of oceans
  • Origin of volcanic islands on top of hot spots

The Jigsaw Puzzle of the Continents
  • Pangaea: the original Earth‘s land mass, surrounded by the ocean Panthalassa (the ancient precursor of the Pacific Ocean)
  • Laurasia & Gondwanaland: evolved by the split-up of Pangaea ca. 200 million years ago Laurasia = today‘s Europe, Asia, and North America; Gondwanaland = today‘s Africa, South America, India, Australia, Antarctica
  • Tethys: separated Laurasia and Gondwanaland; precursor of today‘s Mediterranean Sea
  • Atlantic and Indian Oceans: new oceans created by the movement of continental plates, still continuously enlarging

    Whereas Alfred Wegener (1880-1930) tried to bring together today‘s land mass margins, the puzzel can be nicely solved by working with the 2000 m depth lines (Sir Edward Bullard, 1965).