If the Earth is around 4.6 billion years old, why is the oldest oceanic crust no older than 200 million years?
A) Earth was molten when it formed and took a very long time to cool.
B) Oceanic crust is recycled into Earth's interior at subduction zones.
C) Older oceanic crust was destroyed during the extinction of the dinosaurs.
D) The continents are made of all the old oceanic crust.

Question

Quizplus · Accepted Answer

Oceanic crust is constantly being formed at mid-ocean ridges, but it is also being recycled back into the mantle at subduction zones. This process means that the oldest oceanic crust is no older than 200 million years, because any older crust has been destroyed and recycled into the mantle.

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