Phanerozoic addition rates to the continental crust are calculated by using seismic profiles through magmatic arcs to measure the crustal volumes added during the active lifespans of the arcs. Data for 17 arcs give addition rates per kilometer of arc in the range 20 to 40 km³ km−1 Ma−1. From these data we deduce a world‐wide addition rate of 1.65 km³ a−1 after adding other contributions to the formation of the continental crust, e.g., from hot spot volcanism. We infer a subtraction rate, mainly by subducting sediments, of 0.6 km³ a−1 and arrive at a net crustal growth rate of about 1 km³ a−1. Growth of the continental crust is necessary to maintain approximately constant freeboard, because the secular decline in the heat production of the mantle causes the ocean basins to deepen. An equation for the growth of the continents as a function of the decline in terrestrial heat flow yields approximately constant growth rate since the Archean of 0.9 km³ a−1, in good agreement with the above estimate. On the average, Archean growth rates must have been 3 to 4 times the present rate. Island arc growth rates are inadequate to explain the formation of the Arabian‐Nubian Shield and the Archean granite‐greenstone terrain of the Superior Province, and a captured island chain in Oregon. We confirm the oceanic island origin of the Oregon terrain on the basis of the large growth rates of hotspot islands.

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