1. Development of a Theory
14-2

2. Mid-Ocean Ridge Underwater mountain chain Valley in center
Sediment thinner by ridge
Rocks older farther away

4. Harry Hess US Naval Officer in WWII “Sea floor spreading”
New sea floor at ridge

5. Seafloor Spreading Rift - Magma oozes out onto ocean floor
Plates move away from each other
Sea Floor Spreading - New crust forms

6. Seafloor Spreading
North American Plate is moving away from European and African Plate

10. Normal Polarity
Magnetized objects will point to the north

11. Reversed Polarity
Magnetized objects point to the south

12. Magnetic Reversal Magnetic fields reverse direction
100,000’s of years to millions
Magnetic minerals on ocean floor
Mirrored alternating magnetic stripes on either side of ridge

14. More Evidence Magnetometer – tool Thermal energy Pillow lava
Age and thickness of sediment

15. Magnetic Striping and Seafloor Spreading – You Tube