One of the primary measures of plate tectonics is the history of production of new oceanic lithosphere. As shown by B. Parsons, a direct estimate of the rate of plate creation can be derived from the area/age versus age distribution of the modern oceanic lithosphere. Inversion of the most recent area versus age data (digital isochrons by R.D. Müller et al.) yields a result that the rate of oceanic plate production has not varied significantly since 180 Ma from a mean rate of 3.4 km2/yr. Reconstruction of the cumulative area of subducted lithosphere over the past 90 m.y. is in excellent agreement with a fixed rate of ridge production. The conclusion that the rate of ridge production has not varied significantly contrasts markedly with most existing estimates in which the rate is modeled as decreasing by 50% or more since ca. 100 Ma. A constant rate of ridge production has important implications for models of sea level and p(CO2), among other phenomena that have been linked to variations in global rates of seafloor spreading.

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