The Earth’s crust has a double character. On one hand, there are the continents. Sometimes, the crust that comprises the continents can be older, upwards of 3 to 4 billion years of ages! The oceanic crust that makes up a bulk of the world’s surface area does not get anywhere near. The earliest oceanic crust is just about 220 million years back, or ~ 5% of the age of the Earth. We understand we’ve had oceans and oceanic crust for billions of years, so where has all of it gone?
That’s where subduction is available in. Subduction is the procedure where pieces of the Earth’s crust get actually pushed back into the next layer down (the mantle). The mantle isn’t a stiff strong however rather a plastic strong, so it can warp as the crust gets pressed into it. It likewise isn’t as thick as old crust, so that crust will “sink” through the mantle, possibly winding up at the border in between the mantle and core countless miles listed below our feet.
Standard design of a subduction zone, demonstrating how the oceanic crust is pushed below the continental crust. Credit: Wikimedia Commons.
All crust isn’t the very same. Continental crust is typically 20-40 miles (30-70 kilometers) thick and is made from reasonably low density rock like granite. Oceanic crust is more detailed to 4-6 miles (7-10 kilometers) thick and made from denser rock like basalt. This suggests that when these 2 kinds of plates clash as they carry on the world’s surface area, oceanic crust does not stand an opportunity. It gets pushed beneath the continental crust and pull back into the mantle.
Over the history of plate tectonics in the world, a huge quantity of oceanic crust has actually been recycled back into the mantle through subduction while the continents have actually had the ability to (primarily) withstand this since of their density and buoyancy. Like a Humvee in a demolition derby of Fiats, the continents will not decrease.
Subduction enables tectonics to work due to the fact that if oceanic crust didn’t subduct, we ‘d either require a broadening Earth (which isn’t taking place) or we ‘d have thick layers of thick rock as the oceanic crust folded that would have caused completion of plate tectonics long previously now.
The Atlantic Ocean was born ~ 150 million years back when North and South America divided from Africa and Europe. This procedure continues today with a mid-ocean ridge diminishing the middle of the ocean, moving the existing plates even more apart. We see the volcanism triggered by this in locations like Iceland. No ocean is permanently. The Atlantic Ocean will ultimately start to close as we head towards the next supercontinent.
A map revealing the area of this research study and the 2 present subduction zones in the Atlantic Ocean (Lesser Antilles and Scotia Arcs). Credit: AGI.
Precisely how the ocean basin will start to close is still a secret. You require subduction and there is presently really little of that in the Atlantic Ocean.