Evidence for hot early oceans?

Abstract

The oxygen isotopes in sedimentary cherts (siliceous sediments) have been used to argue that the Precambrian oceans were hot--with temperatures of up to 70 degrees C at 3.3 Gyr before present. Robert and Chaussidon measure silicon isotopes in cherts and arrive at a similar conclusion. We suggest here that both isotope trends may be caused by variations in seawater isotope composition, rather than in ocean temperatures. If so, then the climate of the early Earth may have been temperate, as it is today, and therefore more consistent with evidence for Precambrian glaciations and with constraints inferred from biological evolution.