We propose a unifying explanation for the four major icehouses during the past c.620 million years: earliest Oligocene to Present; early Carboniferous to early Permian; late Ordovician and late Vendian (the ‘snowball Earth’) all of which appear to have been initiated as a result of two plate-tectonic processes. The first moved some continents into polar latitudes; while there the second process opened and closed oceanic low latitude gateways that changed global oceanic circulation from one with important circum-equatorial currents (greenhouse) to one with inhibited circum-equatorial deep-water currents (icehouse) and more restricted oceanic gyres.

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