L4.4: Seafloor Spreading

• SEAFLOOR SPREADING

  ● The main flaw of continental drift theory was that Wegener didn’t know the cause of the drifting.

  ● Harry Hess discovered the phenomenon of seafloor spreading by continuously measuring the seafloor using sonar.
• SEAFLOOR SPREADING

  ● Discovered that the huge, flat ocean floor was broken up by long, tall chains of mountains, frequently divided by a deep rift valley in the middle. Hess postulated that these ridges, now known as mid-ocean ridges, brought new crust to the ocean floor, causing it to widen and push apart in a process he named seafloor spreading.
• Evidence of Seafloor Spreading

  ● Active Fractures

  ● Age of the seafloor rocks

  ● Thickness of the layer of sediments

  ● Patterns of seafloor magnetism
• ● Active Fractures

  ○ A pattern that mimics the shapes of the continental coastlines is visible on the ocean floor.
• ● Age of the seafloor rocks

  ○ It increases as you get further away from the mid-ocean ridge.
• ● Thickness of the layer of sediments

  ○ Increases as you get further away from the mid-ocean ridge.

  ○ Older rocks are exposed to agents of weathering (water) longer thus they are more susceptible to sediments.
• ● Patterns of seafloor magnetism

  ○ Match up with one another on either side of mid-ocean ridges.

  ○ The magnetism is detected from the metals found on the seafloor.