Thursday, May 21, 2009

The Antarctic Plate

When the Tethys Sea opened, 200 million years ago (MYA), Pangea was split into Laurasia (the northern Continents) and Gondwanaland (the southern Continents); future Antarctica, as one might expect, was a component of Gondwanaland. Africa split from its neighbors as the South Atlantic opened, India broke free 80 MYA and Australia drifted away about 55 MYA. Finally, losing its connection with South America, Antarctica settled over the South Pole some 20 MYA.

All of this rifting has resulted from the opening of oceans and seaways (a process that continues today). The rift zones, known as oceanic ridges are not continuously active and, today, the Antarctic Plate is only rifting from the Pacific Plate (along the Pacific-Antarctic Ridge) and from the Australian Plate (along the Southeast Indian Ridge); its borders with the Nazca, South American and African Plates are characterized by a complex of compression faults, transverse faults and subduction zones. Since these margins lie deep beneath the Southern Ocean, they are not yet fully mapped and understood.

For much of the post-Pangea period, Antarctica remained in the Subtropical and Temperate Zones; it was thus home to a wide variety of plants and animals that inhabited these climatic regions. Then, as it drifted to the South Pole, Antarctica's fauna changed and, today, fossils of its warmer past lie entombed beneath its thick coat of ice and snow.