Almost two hundred million years ago, Antarctica was part of the supercontinent Gondwana. At this time Antarctica was much further north and not the dry, cold wasteland of the present-day. Instead, Antartica experienced a tropical climate and was covered by forests and inhabited by ancient lifeforms. Over the course of millions of years Antarctica gradually moved south from near the equator. Sandstone, limestone, and shale built up and the continent grew swampy. As the landmass moved south, the world warmed, leading to much of Antarctica to become a dry, hot desert. Islands began rising from the ocean depths and dinosaurs roamed during this time.
25 million years ago, Gondwana broke apart, though Antarctica, Africa, India, and Australia still formed one landmass. 160 million years ago, Africa was the first to go, followed closely by India about 35 million years later. 66 million years ago Antarctica and Australia still had subtropical climates dominated by coniferous forests and dinosaurs. About 40 million years ago, what is now New Guinea and most of Oceana broke off from Antarctica.
Glacial spread began in stages, first starting around the time New Guinea broke off from the rest of the continent. Ocean currents began to isolate Antarctica from Australia and the ice began to spread, replacing the continent’s coniferous forests. This glacial spread occurred around the same time as the Eocene–Oligocene extinction event 34 million years ago. This extinction event mostly affected aquatic life and resulted in declining levels of carbon dioxide, exacerbating the region’s rapidly expanding ice. For the last 15 million years the continent has been completely covered by ice.