Question #a29c9

1 Answer
Jan 23, 2018

But, every rock on Earth has been formed from the cooling of semi-solid mantle at the crust.


Plate tectonics show us there are major continental and ocean plates with usually, pretty clear boundaries.
It is at the constructive plate boundaries between oceanic plates that a lot of 'new' rock is formed on the planet, this is however the place where new oceanic crust/rock is formed at the mid ocean ridges, however, at the destructive/convergent plate boundaries that oceanic crust is melted back into semi-solid magma below the continental plates.

We also have to remember that a lot of the rock on our planet is constantly recycled, being melted back down, eroded, compacted, heated, dissolved, moved.

Hope this helps.