Thermal isolation of the polar regions is a key condition for glaciation.
The sudden, widespread glaciation of Antarctica and the associ- ated shift towards colder temperatures at the Eocene/Oligocene boundary (,34 million years ago) (refs 1–4) is one of the most fundamental reorganizations of global climate known in the geologic record. The glaciation of Antarctica has hitherto been thought to result from the tectonic opening of Southern Ocean gateways, which enabled the formation of the Antarctic Circum- polar Current and the subsequent thermal isolation of the Antarctic continent5.