Seafloor Spreading

Harry Hess:

  • an american geologist who discovered many flat topped mountains under the pacific ocean in WW2

  • he proposed that new crust was being formed at the ridges, forcing the continents apart

  • he also proposed that in other places the oceanic crust was sinking down, creating trenches (subduction)

Evidence of Seafloor Spreading:

  1. Magnetic Striping

    • magnetite is a mineral found in many rocks

    • a piece of magnetite acts as a compass

    • when molten rock solidifies, all the magnetite lines up in the direction of the earths magnetic field

    • the seafloor has bands of alternating north and south facing magnetite

    • these bands are parallel to the mid ocean ridges (magnetic striping)

    • this is due to the earth’s magnetic field changing every few million years

    • the patterns are symmetrical on both sides

    • therefore new seafloor is being added to each side

  2. Age of the Seafloor

    • when the rocks on the seafloor were dated, we found that the closer the rocks are to the mid ocean ridges, the younger they were

    • this means the seafloor is younger than the continents

    • the oldest seafloor is around 200 million years, and the continents are thousands of million year old

  3. Sediment Thickness

    • in some areas, the ocean ridges are thicker than the rest of the ocean around them, and in some areas the ocean ridges are thinner than the rest of the ocean around it

    • this is because of how the magma rises when the two tectonic plates separate

no wrong

q 1) evidence of continental drift

q 2) explain seafloor spreading, include magnetism

q 3) “suppose a new ocean ridge formed, what could be some results/evidence of this?” (something like that, its about if a new ocean ridge formed, cant remember the rest)

question 1-3 you have an article that you use and can read through to help you answer, but dont rly need it