Download Plate Tectonics 1. Continental Drift

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