Present and Past Glaciations: A Geological Perspective

Abstract

The great global glaciations were a cyclic though rather infrequent phenomenon in the history of the Earth. The Late Palaeozoic (330–270 Ma), the Early Palaeozoic (about 450 Ma), probably also the Late Proterozoic (Vendian: about 600 Ma) glaciations, affected large continents in high latitude south polar position. Asynchronous glaciation affected the southern and the northern continents during the Cenozoic. In Antarctica, it started during Eocene (at about 50 Ma), its ice-cap at sea-level developed in Early Oligocene (at 32–30 Ma), and became a semi-permanent feature of this continent since Early Miocene (22–20 Ma). In the Arctic, the glaciation started much later, during Pliocene (at about 3.4 Ma). Its Pleistocene (2–0.1 Ma) ice-sheets developed around a relatively small Arctic Ocean in northern North America and Eurasia, and in Greenland. Presently, the Arctic glaciation is reduced to a few much reduced ice-caps, the Greenland and the Svalbard ones being the largest. There is a direct correlation between global glaciations and world-ocean level recognizable in Cenozoic marine geological record: low stands of sea level correspond to glacial epochs, while high stands to interglacials. Global-scale glaciations have both terrestrial and extraterrestrial causes.