Seafloor Spreading

Mapped ocean floor

Discovered mid-ocean ridges

Formation of new oceanic crust

• lava erupts at mid-ocean ridge & cools
• forms basalt
• pushes old crust away from mid-ocean ridge (spreading the seafloor)

Youngest rock is near mid-ocean ridge; older rock is farther away

Sediment accumulates on seafloor creating the abyssal plain - more is found farther from mid-ocean ridge

Continents move as the seafloor spreads at the mid-ocean ridge.

Evidence of Seafloor Spreading

• magnetic signature of rocks - basalt has lots of iron (which is magnetic) and as it cools on floor the polarity "freezes"
• evidence of parallel patterns on each side of mid-ocean ridges

Other Evidence

• more heat released from beneath Earth at mid-ocean ridges
• sediment near ridges is younger and thinner