q2 sci theories

• 225 million years ago

  existence of pangea
• Laurasia and Gondwanaland


  north and south
• 150 million years ago


  existence of laurasia (NH) and Gondwana (SH)
• Laurasia - North america (greenland) Europe and Asia
• Gondwanaland - Antarctica, Australia, South America
• 100million years ago


  obvious distance, but not much
• Present


  state of the earth today
• COnintental drift theory

  all continents were a single large landmass "Pangea/pangaea"
• Pangea


  all earth/all land
• Phantalassa


  all sea
• Father of plate tectonics


  ALfred wegener
• 1912


  proposed continental drift theory
• 1915


  published book "the origin of continents and oceans"
• alfred wegener is


  a german meteorologist and geophysicist
• evidences of continental drift theory

  • topographic evidence - geologically 'fit'
  • fossil correlation - mesosaurus fossils found on eastern coast of south america, western of africa
  • rock and mountain correlation - gondwana sequence
  • paleoclimatic data - bituminous coal deposits, glacial striations
• gondwana sequence


  identical pattern of rocks and fossils located in southern hemisphere
• challenges of continental drift theory

  • lack of mechanism for movement
  • land bridge theory
  • uniformitarianism
  • scientific conservatism
  • technological limitations
• wegener suggested that continents moved due to


  centrifugal force from earths rotation and tidal forces (tides) from the moon and son
• land bridge theory


  continents were connected by submerged land bridges
• uniformitarianism 


  idea that the earths features formed slowly over time
• scientific community was

  resistant
• wegeners profession

  did not align with his theory, making scientists doubt his credibility
• technology back then couldnt 


  measure slow continental movement or its underlying mechanisms
• seafloor spreading


  geologic process in which tectonic plates split apart from each other
• seafloor spreading occurs at


  divergent boundaries
• As tectonic plates slowly move away from each other


  heat from the mantle’s convection currents makes the crust more plastic and less dense
• seafloor spreading happens at


  mid ocean ridges
• the seafloor spreading process is


  slow, moving a few cm per year
• proponent of seafloor spreading theory


  harry hammond hess
• echo sounding


  sonar
• 1960


  proposed seafloor spreading theory
• 1962

  published book 'the history of ocean basins'
• process of seafloor spreading

  1. divergence of plates
  2. magma rises
  3. movement of crust
  4. age of crust
  5. recycling of crust
• new rocks are closer to the ridge
• old rocks are farther away
• evidences of seafloor spreading

  • age of ocean floor
  • sediment deposits
  • hydrothermal vents
  • magnetic stripes
• oceanic crust is mainly igneous rock basalt
• age of ocean floor increases the farther away it is from the ridge
• thickness of sediments deposited on the ocean floor increases as you go farther from the ridge
• hydrothermal vents - when water turns into steam due to being heated up by magma after it seeps through the gaps