If new lithosphere is generated at the mid ocean ridges, why isn't the earth
expanding as new crust is made?
-subduction causes the lithosphere to be recycled at plate boundaries
-collision boundaries cause the lithosphere to be recycled at plate boundaries
-transformation causes the lithosphere to be recycled at plate boundaries

-Subduction causes the lithosphere to be recycled at plate boundaries

At destructive boundaries, tectonic plates collide, the denser plate gets subducted under the less dense plate. The subducted plate dives into the mantle, melts and is recycled.

Explanation:

At the constructive boundary, as two plates move away from each other, magma from the mantle rises to occupy the void. The magma cools to form new crust in between the two plates.

As new crust is formed at the constructive boundaries and old crust is destroyed at destructive boundaries this maintains a balance that ensures the crust is maintained more or less the same size over time. The only difference is that the crust shift position due to these tectonic plates movements driven by convection currents of the mantle.

Learn More:

For more on plate boundaries check out;

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