A note on continents and the Earth’s Urey ratio

The Urey ratio (mantle heat production divided by heat loss) is a key constraint for thermal history models. Recent Urey ratio estimates are in the range of 0.21–0.49. It has been well noted in the literature that classic thermal history models predict a larger value. The extent of the discrepancy is considered significant enough to be deemed a paradox. The ‘Urey ratio paradox’ has motivated a number of studies and some considerable debates. Classic thermal history models, and the majority of those that have followed, do not explicitly consider the effects of continents. For consistency, the present day observations they seek to match should be adjusted to account for continents. We use mantle convection simulations with continents to argue that the adjusted ratio shifts to 0.33–0.76. Classic thermal history models predict a Urey ratio that, although at the high end, is within this range. This suggests that the ‘paradox’ has been exaggerated. It also points toward a first-order role for continents in the Earth’s thermal evolution

► We examine the effects of continents on the Earth’s thermal state and Urey ratio.
► Continents lower the Earth’s Urey ratio.
► Continents increase mantle potential temperature.
► Continental growth lowers the level of mantle potential temperature changes over geologic time