Tectonic-climatic supercycle in the billion-year plate-tectonic eon: Permian Pangean icehouse alternates with Cretaceous dispersed-continents greenhouse

The earth alternates in a supercycle 400 m.y. long from a single continent (Pangea) and ocean (Panthalassa) with an icehouse climate to many continents and oceans with a greenhouse climate. The supercycle is driven by the heat that accumulates beneath the insulator of Pangea, and the greenhouse is made by the excess CO₂ vented from the mantle during the faster rate of plate activity. In the current supercycle (A) since the mid-Carboniferous (320 Ma), the growth and decay of Pangean heat is observed in globally synchronous cratonic sedimentary sequences that represent, in ascending order: (1) a stratigraphic gap, (2) sagging, (3) rifting, (4) fast, and (5) slow seafloor spreading. Stages 4 and 5 of the previous supercycle (B) are observed back to the start of the Phanerozoic; in the Proterozoic, earlier stages of B are postulated back to 720 Ma and a third supercycle (C) to 1100 Ma. The big glaciations of the latest Proterozoic (700-600 Ma) and Late Palaeozoic (320-260 Ma) are confined to the icehouse state during stages 1-3; the Sturtian (800 Ma), latest Ordovician (440 Ma), and Quaternary (2-0 Ma) glaciations fall within greenhouse states during stage 5 of slow seafloor spreading. The next icehouse glaciation is expected 80 Ma hence. The problem of long-term past (and future) climate change is soluble by global studies. Urgently needed are (1) global stock-takes of (a) the rate of granite emplacement, which serves as a proxy via plate activity for the mantle source of atmospheric CO₂, and (b) carbonate sinks and other sedimentary indicators of CO₂; and (2) the extension of the sea-level curve back past 570 Ma to the start of the plate-tectonic eon 1100 Ma ago. From such studies, environmental baselines for past climatic states can be drawn for gauging present and future "background" variations.