This was only the second time that Earth reached this level of warmth since the Precambrian. The other time was during the Cambrian Period, which ran from 541 million years ago to 485.4 million years ago. During the early Eocene, Australia and South America were connected to Antarctica.  53 million years ago during the Eocene Epoch, summer high temperatures in Antarctica were around 25 °C (77 °F). Temperatures during winter were around 10 °C (50 °F). It did not frost during the winter. The climate was so warm that trees grew in Antarctica. "Arecaceae" (palm trees) grew on the coastal lowlands, and "Fagus" (beech trees) and "Pinophyta" (conifers) grew on the hills just inland from the coast. Temperatures soon began to decrease as the methane levels in the atmosphere started to decline. As the global climate became cooler, the planet was seeing a decrease in forests, and an increase in savannas. Animals were evolving to have a larger body size. Australia drifted away from Antarctica forming the Tasmanian Passage, and South America drifted away from Antarctica forming the Drake Passage. This caused the formation of the Antarctic Circumpolar Current, a current of cold water surrounding Antarctica. This current still exists today, and is a major reason for why Antarctica has such an exceptionally cold climate. The Eocene-Oligocene Boundary 33.9 million years ago was the transition from the last greenhouse period to the present icehouse climate. At this point CO2 levels had dropped to 750 ppm. This was the beginning of the Late Cenozoic Ice Age. This was when the ice sheets reached the ocean, the defining point.  33 million years ago was the evolution of the thylacinid marsupial ("Badjcinus"). The first balanids, cats, eucalypts, and pigs came about 30 million years ago. The brontothere and embrithopod mammals went extinct at this time. At 29.2 million years ago, there were three ice caps in the high elevations of Antarctica. One ice cap formed in the Dronning Maud Land. Another ice cap formed in the Gamburtsev Mountain Range. Another ice cap formed in the Transantarctic Mountains. At this point, the ice caps weren't very big yet. Most of Antarctica wasn't covered by ice. By 28.7 million years ago, the Gamburtsev ice cap was now much larger due to the colder climate.