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Download Plate Tectonics 1. Continental Drift
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Transcript
Plate Tectonics 1: Continental Drift - Continental drift was a hypothesis proposed by Alfred Wegner (German Scientist) in 1912 -Said all continents were once one large land mass and began to separate 200 MYA to the world we see today -He called this supercontinent Pangea -Evidence for hypothesis 1) Similar coastlines, continents are shaped like a jigsaw puzzle 2) Identical fossils along joining coasts -Ex. South America and Africa 3) Identical Age and rock types along joining coasts -Ex. Brazil and West Africa 4) Similar mountain chains across joining coasts -Ex. Appalachians and mountains in Scotland and Northern Europe 5) Climactic changes seen in geologic record -Pangea once positioned over South Pole forming glaciers in South Africa and South America -Coal deposits in North America (once covered by tropical or subtropical swamps) -Wegner didn’t know mechanism for this process so his hypothesis of moving continents wasn’t accepted. -He died in 1930 doing research in Greenland and never found a mechanism for moving continents. -Later support for continental drift 6) Sea floor spreading -Young rocks found along Mid-Atlantic ridge in 1947 -Ridge is a break in the Earth’s crust -Ocean floor is moving away from ridge with new magma filling the gap -Ocean floor moving = continents moving 7) Paleomagnetism -Earth is a giant magnet, aligns compass to magnetic north -Magma rises and cools along mid-ocean ridges and minerals orient themselves with Earth’s magnetic field, pointing North or South -Creates bands of rock oriented North and South -Dating rocks proved Earth’s EM field has reversed in the past -This was enough to finally support Wegner’s hypothesis