1. Evidence after wegener: seafloor spreading and PALEOMAGNETISM
2/10/16
Evidence after wegener: seafloor spreading and PALEOMAGNETISM
Objective: I will elaborate on the concepts of seafloor spreading and magnetic striping, used as evidence for the Theory of Plate Tectonics.
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2. Mid-Ocean Ridges
prior to 1940, scientists thought the seafloor was flat
after WWII, new submarine technology used to map the ocean floor
they discovered a worldwide underwater mountain range
called it the Mid-Ocean Ridge
this led to new curiosity about Earth’s crust

3. Mid-Ocean Ridges

4. Seafloor Spreading
Harry Hess developed the idea of seafloor spreading (1962) by looking at the ages of oceanic crust
oldest continental crust ~4 billion years old, oldest oceanic crust only ~175 million years old

5. Seafloor Spreading
crust was younger by mid-ocean ridges and older further away from the ridge
Hess proposed that new oceanic crust was being made at cracks in the Mid-Ocean ridge called rifts

6. Seafloor Spreading

7. Paleomagnetism
Earth’s magnetic field has flipped many times in history
when new crust is formed, it “locks in” the current magnetic field direction of Earth
normal polarity- magnetic fields that point north
reverse polarity- magnetic fields that point south

8. Paleomagnetism
scientists noticed an alternating pattern of normal and reverse polarity in oceanic rocks
this proved that oceanic crust is created at different times, supporting seafloor spreading

9. Magnetic Striping and Symmetry