Technological advances had helped reveal that the ocean floor was not flat, as once believed, but instead was marked by 50,000-kilometer-long, 3,000-meter-high ridges and 11-kilometer-deep trenches. How do scientists explain why, if new crust is constantly being formed from volcanic materials at the ridges, Earth's crust stays the same size?

A) Seafloor spreading is the cause of new crust being added. Old crust crumbles and forms mountains throughout the Earth's surface. Mountains keep growing.
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B) Scientists hypothesize that new crust is the result of volcanic activity throughout the Earth's surface and older magma is destroyed as it subducts during earthquakes into Earth's mantle.
C) Scientists found that the youngest oceanic crust is located nearest the mid-ocean ridge and divergent boundary and the oldest crust is at subduction zones where it sinks back into the Earth.
D) Scientists found that the oldest oceanic crust is located nearest the mid-ocean ridge and forms from volcanic activity;the youngest crust is nearest the trenches and it comes from magma flowing up to Earth's surface..