Dissipation of more heat from a hotter early Earth by the plate-tectonics mechanism would require subduction of, on average, younger lithosphere. In principle, this could be achieved equally well by faster spreading, by having greater ridge length, or some combination thereof. Present-day evidence, however, suggests that younger oceanic lithosphere subducts more slowly than older; if this applied in the Archean, then the “greater ridge length” alternative prevailed. A quantitative expression is derived which indicates that oceanic heat loss is proportional to the cube root of ridge length. This relationship means that if Archean heat flow was 3 times that of the present, 27 times as much ridge would have been required, which would suggest that the Archean Earth was covered by many small plates moving slowly.

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