HI! We may not see notice it but plate tectonics actually have a "recycle" process. However, scientist reported that it happens in a span of 500 million years. Over the years, the oceanic crusts are pressured to the topmost layer of the mantle causing the oceanic crusts to melt and mix with the Earth's mantle. Such crust blending results to the formation of volcanoes underwater. In time, the said volcanoes would erupt causing the formation of new oceanic and continental crusts.