Late Cenozoic Ice Age

The Late Cenozoic Ice Age, also known as the Antarctic Glaciation, began about 34 million years ago at the Eocene-Oligocene Boundary and continues today. It marks the start of Earth's current ice age or icehouse period, characterized by the growth of large ice sheets, especially in Antarctica. The formation of the Antarctic ice sheets was a key event that defined this period.

About six million years after it began, the East Antarctic Ice Sheet had formed, and by 14 million years ago, it had reached its present size. In the last three million years, glaciers began to spread into the northern hemisphere. This started when Greenland gradually became covered by an ice sheet during the late Pliocene.

During the Pleistocene Epoch, which began about 2.58 million years ago, the Quaternary glaciation developed. This period saw temperatures drop and large swings between cold glacial periods and warmer interglacial periods. During the cold glacial periods, massive ice sheets covered much of northern North America and northern Eurasia, shaping the landscapes we see today.

Late Cenozoic Ice Age 33.9 million years ago to present Divisions within the current ice age For divisions prior to 33.9 million years ago, see Geologic time scale
Period	Epoch	Age
↑ Paleogene	Oligocene 33.9 to 23.03 Ma (last epoch of the Paleogene Period)	Rupelian 33.9 to 27.82 Ma
		Chattian 27.82 to 23.03 Ma
Neogene	Miocene 23.03 to 5.333 Ma	Aquitanian 23.03 to 20.44 Ma
		Burdigalian 20.44 to 15.98 Ma
		Langhian 15.98 to 13.82 Ma
		Serravallian 13.82 to 11.63 Ma
		Tortonian 11.63 to 7.246 Ma
		Messinian 7.246 to 5.333 Ma
	Pliocene 5.333 to 2.58 Ma	Zanclean 5.333 to 3.6 Ma
		Piacenzian 3.6 to 2.58 Ma
Quaternary	Pleistocene 2.58 Ma to 11.7 ka	Gelasian 2.58 to 1.8 Ma
		Calabrian 1.8 Ma to 774 ka
		Middle Pleistocene ("Chibanian") ("Ionian") 774 to 129 ka
		Upper/Late Pleistocene ("Tarantian") 129 to 11.7 ka
	Holocene 11.7 ka to present	Greenlandian 11.7 to 8.2 ka
		Northgrippian 8.2 to 4.2 ka
		Meghalayan 4.2 ka to present
The Late Cenozoic Ice Age falls within the Cenozoic Era which started 66 million years ago. The Cenozoic Era is part of the Phanerozoic Eon which started ~538.8 million years ago. In standard nomenclature the Pleistocene Epoch lasts from 2.58 Ma to 11.7 ka and the Holocene epoch lasts from 11.7 ka to present. However, it is disputed whether these should in fact be treated separately, or whether the "Holocene" is in fact merely a Pleistocene interglacial. See below for details.

History of discovery and naming

In 1837, a German naturalist named Karl Friedrich Schimper first used the term Eiszeit, which means ice age. At first, this term described only the cold periods when glaciers grew. Later, scientists began to understand that these cold periods were part of a much longer ice age.

Today, we know that Earth has been in an ice age for about 30 million years. The name "Late Cenozoic Ice Age" has been used by scientists since at least 1973.

The climate before the polar ice caps

The last greenhouse period began 260 million years ago during the late Permian Period and lasted until 33.9 million years ago. This was a time when the Earth was very warm, especially during the Late Paleocene to Early Eocene, about 65 to 55 million years ago. During this warmest time, called the Paleocene–Eocene Thermal Maximum, average global temperatures were around 30 °C (86 °F).

Back then, Australia and South America were connected to Antarctica. In the early Eocene, around 53 million years ago, Antarctica had very mild winters with no frost, and trees like palms, beeches, and conifers grew there. As the climate slowly cooled, forests began to shrink and savannas started to appear, while animals evolved to become larger.

Glaciation of the southern hemisphere

Australia moved away from Antarctica, creating the Tasmanian Passage. South America also moved away, forming the Drake Passage. These changes led to the creation of the Antarctic Circumpolar Current, a cold water current that circles Antarctica and helps keep it very cold today.

About 34 million years ago, at the Eocene-Oligocene Boundary, the climate changed from a warm greenhouse period to the cooler icehouse climate we have now. This was when Antarctica began to freeze over, forming large ice sheets. Over millions of years, these ice sheets grew larger, eventually covering most of the continent. By about 15 million years ago, Earth experienced a warmer period called the Mid-Miocene Climatic Optimum, but the ice sheets in Antarctica remained much like they are today. Later, glaciers also began to form in the mountains of the Northern Hemisphere.

Glaciation of the northern hemisphere

The ice in the Arctic of the Northern Hemisphere began to grow during the late Pliocene, about 3 million years ago, when Greenland started to freeze over. This happened around the same time that an isthmus formed between North and South America, changing ocean currents and making winters in the North Atlantic colder.

Today we live in the Quaternary period, which began 2.58 million years ago. This time is split into the Pleistocene, which ended 11,700 years ago, and the current Holocene. During the Quaternary, Earth has gone through many cold times with huge ice sheets, called glacial periods, and warm times with less ice, called interglacial periods. These changes happen because of long-term shifts in Earth’s tilt and orbit, known as Milankovitch cycles.

Last Glacial Period

The Last Glacial Period began 115,000 years ago and ended 11,700 years ago. During this time, large ice sheets grew and moved into many parts of the Northern Hemisphere.

Around this time, humans known as Homo sapiens left Africa and spread to new places. They met and sometimes mixed with other early human groups, such as Neanderthals. The Last Glacial Maximum was the coldest part of this period, occurring between 26,500 and 20,000 years ago, when ice covered even more land than before.

Holocene

The Earth is currently in a warm period called the Holocene epoch, which is part of a longer ice age. Although this time has less ice than the last glacial period, there is still more ice today than there was millions of years ago, when only Antarctica had ice sheets. Today, ice covers about 3.1% of Earth's surface and 10.7% of its land area.

Scientists think this warm period might last longer than usual due to human activities that increase greenhouse gases in the atmosphere. Even so, the climate is expected to cool in about 25,000 to 50,000 years from now. However, the extra greenhouse gases may prevent the next glacial period from starting until much later, perhaps 125,000 to 150,000 years from now.

Main article: Holocene climatic optimum