1. Alfred Wegener first proposed the theory of continental drift in 1912, suggesting that the continents were once joined together in a supercontinent called Pangaea before slowly drifting apart.
2. Wegener provided four lines of evidence to support his theory - similar rock formations and fossils on separated continents, matching coastlines, correlated climate indicators like coal deposits, and plant and animal distributions that could not have crossed oceans.
3. However, Wegener's theory was initially rejected because he could not explain what caused the continents to move. It was not until the 1950s-60s that seafloor spreading and plate tectonics were discovered, providing a mechanism to explain continental drift.
18. FINDING EVIDENCE The first way to map the ocean floor used Sonar. This way stunk because it didn’t accurately map the floor.
19. The then invented the Magnetometer. This could detect small changes in the magnetic field in rocks and map them.
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21. Seafloor Spreading – new ocean crust is formed at ocean ridges and destroyed at deep sea trenches.
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23. Convection current/Plate motion Plate motion is thought to be caused by convection currents in the asthenosphere. Since the hotter material deep in the asthenosphere is less dense it will slowly rise, as it reaches the base of the lithosphere it begins to cool, become more dense, and will sink. Rising convection currents will move plates apart (divergent), while sinking convection currents will move plates together (convergent). http://news.bbc.co.uk/nol/shared/spl/hi/pop_ups/04/world_how_volcanoes_erupt/img/1.jpg
26. These new maps showed the different magnetism in different layers of rock. As new crust is created the iron bearing minerals point to where the magnetic pole is at the time of creation. This is called Paleomagnetism
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29. This proved that new sea floor was being created at mid-ocean ridges. Identical magnetism on opposite sides of ridges. Thus, the plates where moving.