EARTH SCIENCE
TECTONICS
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Crust is destroyed at the same time it is created
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New crust is underwater where it sinks
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New crust breaks more easily than old crust
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None of the above
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Detailed explanation-1: -Given that Earth’s surface is mostly constant in area, you cannot make crust without destroying a comparable amount of crust. With convection of the underlying mantle, we see insertion of mantle magma along mid ocean ridges, constantly forming new oceanic crust.
Detailed explanation-2: -New crust is continually being pushed away from divergent boundaries (where sea-floor spreading occurs), increasing Earth’s surface. But the Earth isn’t getting any bigger. What happens, then, to keep the Earth the same size? The answer is subduction.
Detailed explanation-3: -At subduction zones, the edge of the denser plate subducts, or slides, beneath the less-dense one. The denser lithospheric material then melts back into the Earth’s mantle. Seafloor spreading creates new crust. Subduction destroys old crust.
Detailed explanation-4: -When two plates are moving away from each other, we call this a divergent plate boundary. Along these boundaries, magma rises from deep within the Earth and erupts to form new crust on the lithosphere. Most divergent plate boundaries are underwater and form submarine mountain ranges called oceanic spreading ridges.
Detailed explanation-5: -Why is Earth not growing in spite of sea floor spreading? because of subduction the Pacific Ocean.