PLATE TECTONICS.pptx - PLATE TECTONICS A DRIFTING CONTINENTS 1 Alfred Wegner proposed the Theory of Continental Drift in early 1900\u2019s \u2022Wegner\u2019s


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1. Alfred Wegner proposed the Theory of Continental Drift in early 1900’s. A. DRIFTING CONTINENTS Wegner’s theorized that all the continents were once a single landmass about 245 million years ago that gradually drifted apart (are still drifting). Called this supercontinent Pangea which is Greek for “all Earth” The land masses Split again – Laurasia & Gondwana 180 million years ago
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2. Evidence for Pangaea a.Continents fit together like puzzle pieces b.Fossils of the same plants and animals are found on different continents **climate evidence supports this c.Mountains that appear on one coastline had similar formations and rocks on opposite coastlines BUT>>>>>Wegner couldn’t
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Matching Mountain Ranges
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Glacier Evidence
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1950’s-mapping of the seafloor found Mid- ocean Ridges -huge underwater mountain chains found in every ocean around the Earth a. They formed along cracks in the crust where molten rock pushed up and out in a process called Sea Floor Spreading younger rock found closer to ridge than on continents. Earth DOESN’T get larger because oceanic crust is destroyed along deep-ocean trenches, where the oceanic plates sink into the asthenosphere 3. How did plates move then?
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