Billions of compressed leaves and wood fragments have generated thick coal beds in Antarctica. Palaeobotanist Andrew Drinnan for scale.
Antarctica and Gondwana were amalgamated into the megacontinent Pangea during the Mesozoic. The enormous scale of this megacontinent (reaching almost pole-to-pole) meant that cool polar ocean currents were deflected to mix with warm equatorial waters, creating oceans with relatively even, mild temperatures. This helped to maintain the ice-sheet-free greenhouse world of the Mesozoic. However, Pangea started to break up in the Jurassic and piece after piece began to separate throughout the Cretaceous.
Antarctica remained connected to South America and Australia until about 35 million years ago and, up to that time, retained a diverse flora. At the end of the Eocene, both Australia and South America pulled away northwards allowing the South Circumpolar Current to develop – an ocean current that maintains a continuously flowing pool of cold water around Antarctica. Once this cold-water current was established, it trapped Antarctica in a frigid grip.
Ice caps began to develop on the highlands then rapidly linked up to form an extensive ice sheet. The ice has advanced and retreated many times with changes in the global climate and hardy plants such as the southern beech trees (Nothofagus) managed to linger on in isolated Antarctic refugia until as recently as five million years ago. However, intensified global cooling since that time has eliminated all woody plants and the ice sheet is now four kilometres thick at its center.
Cross-section of Permian fossil wood showing prominent seasonal growth rings.