New plate material is being added to the edges of plates, and NO plate material is being removed.
Plate material is being removed from the edges of plates, and no new plate material is being added.
New plate material is being added to the edges of plates, and the same amount of plate material is being broken into pieces and carried away.
New plate material is being added to edges of plates and the same amount of plate material is being crumpled upward or recycled bacck into the earth's interior.
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