Seafloor Spreading

Diagram and explanation of seafloor spreading, specifically for ocr twenty first century. Includes higher tier information. I hope its useful :)

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Seafloor Spreading (OCR 21C)
Seafloor spreading happens when magma from the liquid part of the
mantle rises comes to the surface with enough force to move the solid part
of the mantle and tectonic plates. It hardens to form new oceanic crust
(seafloor) which pushes the existing floor outwards. Seafloor spreads in this
way about 10cm every year.
Higher Tier
The Earth's magnetic field changes polarity every million years or so. So
when seafloor spreading occurs it produces stripes of rock of alternating
polarity. From this geologists can work out how quickly new oceanic crust
is forming.

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