evidence of plate movement

• Continental Drift Theory


  Alfred Lothar Wegener (1880-1930) hypothesized in 1912 that the continents are slowly drifting around the Earth and is once a large landmass called Pangaea, a Greek word which means "All Earth"
• How Wegener discovered continental drift

  1. Alfred was struck by the resemblance between the continents and ice-floes in the arctic oceans, resulting from the break-up of sheets of floating sea-ice

  2. He noticed the edges of South America and Africa in a World Map could be fitted like a jigsaw puzzle
• Fatal flaw of Wegener's Theory

  • Lack of a mechanism to explain how the continents moved
• Continents are drifting
• Evidence gathered by Wegener to support Continental Drift Theory

  • Fossil evidence
  • Geological "fit" evidence
  • Glacial and coal deposits evidence
  • Biogeographic evidence
• Mesosaurus


  A type of reptile, similar to the modern crocodile, which propelled itself through the water with its long hind legs and limber tail. Its remains are found solely in South Africa and Eastern South America.
• Cynognathus


  A mammal-like reptile roaming the terrains during the Triassic period, as large as a modern wolf. Its fossils are found only in South Africa and South America.
• Lystrosaurus


  A "shovel reptile," thought to have been a herbivore with a stout built like a pig. Its fossils are only found in Antarctica, India, and South Africa.
• Glossopteris


  A genus of extinct seed ferns which closely resemble ferns, found in Australia, Antarctica, India, South Africa, and South America—all the southern continents.
• Pangaea


  All Earth
• Evidences presented by Wegener

  • Fossil evidence
  • Geological "fit" evidence
  • Glacial and coal deposits
  • Biogeographic evidence
• Continental drift hypothesis

  The continents are slowly drifting around the Earth and is once a large landmass called Pangaea
• Wegener's Theory lacked a mechanism to explain what drives the continents to move
• Seafloor Spreading Theory


  Proposed by Harry Hess, it explains what causes continents to move
• Seafloor spreading


  The idea that the Earth's crust had been moving away on each side of oceanic ridges, down the Atlantic and Pacific oceans, that were long and volcanically active
• What Harry Hess and his men accidentally discovered when exploring the oceanic floor


  • The bottom of the sea was not as smooth as expected, but full of canyons, trenches and volcanic sea mountains
  • The oceans were shallower in the middle and he identified the presence of Mid Ocean Ridges, raised above the surrounding generally sea floor (abyssal plain) by as much as 1.5 km
• Relationship between seafloor spreading and continental drift

  As the seafloor spreading occurs, the continents move
• Magnetic reversals are believed to occur when small, complex fluctuations of magnetic fields in the Earth's outer liquid core interfere with the Earth's main dipolar magnetic field to the point where they overwhelm it, causing it to reverse
• Magnetic Reversal


  1. Rocks of the same age in the seafloor crust would have taken on the magnetic polarity at the time that part of the crust formed

  2. Surveys of either side of the Mid-Atlantic Ridge showed a symmetrical pattern of alternating polarity stripes
• Over the last 10 million years, there had been an average of 4 to 5 reversals per million years. New rocks are added to the ocean floor at the ridge with approximately equal amounts on both sides of the oceanic ridge