During the Triassic Period, about 200 million years ago (MYA), the supercontinent of Pangea split into Laurasia (the northern Continents) and Gondwana (the southern continents). Throughout the Jurassic and Cretaceous Periods (190-65 MYA), as dinosaurs roamed the globe, Laurasia and Gondwana rifted into the continents that we recognize today.
Late in the Cretaceous, about 80 MYA, Australia and Antarctica remained connected but a rift began to form from west to east, opening a long, narrow bay between the continents; nevertheless, they retained a connection via the Tasmanian Bridge. Throughout most of the early Cenozoic Era (65-40 MYA), Earth's climate was very warm and, despite its gradual movement to the south, the Australian-Antarctic land mass harbored diverse, temperate ecosystems. Then, near the end of the Eocene (about 38 MYA), the southern end of the Tasmanian Bridge split from Antarctica, the Tasmanian Strait opened and Australia drifted toward the north (a process that continues today). This produced a circumpolar ocean current around Antarctica, cooling that continent and Earth's climate as well; indeed, the Antarctic ice sheet began to form at that time.
The connection between Tasmania and the Australian mainland has since opened and closed as sea levels have fallen (during glacial epochs) and risen (during warm interglacial periods), respectively. Humans reached Australia about 60,000 years ago, crossing (perhaps accidentally) from Indonesia; by 30,000 years ago, some of these native Australians had colonized Tasmania, then a peninsula of southeastern Australia. About 12,000 years ago, as the last Pleistocene glaciers receded, sea levels rose and Bass Strait reformed, isolating the Tasmanian residents from mainland aborigines.
