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. Page 61

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

Mid-Ocean Ridges

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

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

Seafloor Spreading

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

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

Magnetic Striping and Symmetry