The Late Cenozoic Ice Age, or Antarctic Glaciation, began 34 million years ago at the Eocene-Oligocene Boundary and is ongoing. It is Earth's current ice age or icehouse period. Its beginning is marked by the formation of the Antarctic ice sheets.
Six million years after the start of the Late Cenozoic Ice Age, the East Antarctic Ice Sheet had formed, and 14 million years ago it had reached its current extent.
In the last three million years, glaciations have spread to the northern hemisphere. It commenced with Greenland becoming increasingly covered by an ice sheet in late Pliocene (2.9-2.58 Ma ago) During the Pleistocene Epoch (starting 2.58 Ma ago), the Quaternary glaciation developed with decreasing mean temperatures and increasing amplitudes between glacials and interglacials. During the glacial periods of the Pleistocene, large areas of northern North America and northern Eurasia have been covered by ice sheets.
History of discovery and naming
In 1837, German naturalist Karl Friedrich Schimper coined the term , meaning ice age (or ice tide for a more literal translation). For a long time, the term referred only to glacial periods. Over time, this developed into the concept that they were all part of a much longer ice age.
The concept that the earth is currently in an ice age that began around 30 million years ago can be dated back to at least 1966.
As a geologic time period, the Late Cenozoic Ice Age was used at least as early as 1973.
The climate before the polar ice caps
The last greenhouse period began 260 million years ago during the late Permian Period at the end of the Karoo Ice Age. It lasted all through the time of the non-avian dinosaurs during the Mesozoic Era, and ended 33.9 million years ago in the middle of the Cenozoic Era (the current Era). This greenhouse period lasted 226.1 million years.
The hottest part of the last greenhouse earth was the Late Paleocene - Early Eocene. This was a hothouse period that lasted from 65 to 55 million years ago. The hottest part of this torrid age was the Paleocene–Eocene Thermal Maximum, 55.5 million years ago. Average global temperatures were around . 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 538.8 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 . Temperatures during winter were around . 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.
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.
Glaciation of the southern hemisphere
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, when ~25% more of Antarctica's surface was above sea level and able to support land-based ice sheets relative to today, 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.