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Continents change position over time. Alfred Wegener Evidence Hypothesis – continental drift Earths continents were once joined Super Continent called.

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Presentation on theme: "Continents change position over time. Alfred Wegener Evidence Hypothesis – continental drift Earths continents were once joined Super Continent called."— Presentation transcript:

1 Continents change position over time

2 Alfred Wegener Evidence Hypothesis – continental drift Earths continents were once joined Super Continent called Pangaea Fossils Climate geology

3 Fossils Climate Geology Mesosaurus – found on the west coast of Africa and the east coast of South America Ice scratches on South America Tropical plant fossil in Greenland Rocks that make up the continents North America lines up with Scotland

4 Theory Sea Floor Evidence Evidence and explanations lead to the Theory of Plate Tectonics Sea Floor Spreading Age of the Sea Floor Trenches

5 Sea Floor Spreading Age of the Sea floor Ridges form on the sea floor As the plates move apart molten rock pushes up Called spreading centers Mid-Atlantic Ridge The rocks are older the further you move away from the spreading centers

6 Ocean Trenches Size of earth Deep canyons on the ocean floor Dense crust is sinking into the asthenosphere Earth isnt changing size because at the same rate that new crust is forming (at spreading centers), old crust is being destroyed (at trenches)

7 How does it happen? Convection Currents – Hot molten rock rises – Cooled rock sinks – Moves the tectonic plates like a conveyer belt

8 Convection Currents

9 Hypothesis becomes theory Based on the facts from the ocean floor the hypothesis of Continental Drift becomes the Theory of Plate Tectonics


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