Glacials

Glacials, also known as Ice Ages, were the periods of time in which the northern and southern hemispheres were extensively covered by ice sheets. Glacials occurred during the Pleistocene Epoch (2.58 Ma to 10 ka), ranging from the Biber/Tegelen and Pre-Illinoian Glacials of the Gelasian Stage to the Würm/Wisconsin Glacial (often called the "Last Ice Age"), the end of which marks the beginning of the Holocene Epoch.

Cenozoic Era

The current Cenozoic Era, which began 66 Ma, is divided into three Periods: the Palaeogene (66 Ma to 23 Ma), the Neogene (23 Ma to 2.58 Ma), and the ongoing Quaternary from 2.58 Ma. The combined spans of the Palaeogene and the Neogene were once termed the Tertiary Period, but this classification became obsolete in 2004. Unlike Periods in the earlier Eras, the Periods of the Cenozoic are sub-divided into Epochs. The Palaeogene had three: the Palaeocene, Eocene and Oligocene. The Neogene had two: the Miocene and Pliocene. The Quaternary has the Pleistocene and the Holocene.

Hominids

It was during the Pliocene Epoch (5.33 Ma to 2.58 Ma), that the evolution of hominids first became apparent in Africa. Following the Pliocene, the Pleistocene featured abundant Glacial expansion during the so-called Ice Ages and the evolution of hominids from australopithecus afarensis via homo habilis and homo erectus to homo sapiens sapiens. Homo habilis had a larger brain and body than australopithecus afarensis and is believed to have been the first hominid to use stone tools.

Pleistocene Epoch

The significant factor of the Pleistocene Epoch (2.58 Ma to 11.7 ka) is glaciation and there were several Glacial Stages, commonly known as Ice Ages; and Interglacial Stages, in which glaciers alternatively advanced or retreated. It was in this Epoch that homo habilis evolved via homo erectus into homo sapiens sapiens. During that evolution, humans began 1.5 Ma to make tools and weapons using the basic materials of wood and stone: this was the beginning of the Palaeolithic Age (Old Stone Age).

The International Commission on Stratigraphy (ICS) has sub-divided the Pleistocene into four Ages/Stages and their corresponding rock units: the Gelasian (2.58 Ma to 1.8 Ma); the Calabrian (1.8 Ma to 774 ka); the Chibanian (774 ka to 129 ka); and the relatively short Upper Pleistocene (129 ka to 11.7 ka). The latter has unofficially been termed "Tarantian" but it currently (2024) awaits official naming and ratification by the ICS. These divisions are international but there are various regional sub-divisions too.

It is worth mentioning that a Stage is a succession of rock strata laid down in a single Age on the Geological Timescale (GTS), a system of chronological dating that uses chronostratigraphy – the process by which strata is related to time – and geochronology – determination of the age of rocks. A Stage usually represents millions of years of deposition but the Ages of the Quaternary Period are thousands of years. An Age is the smallest hierarchical geochonologic time unit and is the equivalent of a chronostratigraphic Stage, meaning that a given Stage of rock and the corresponding Age of time will by convention have the same name, and the same boundaries. So, for example, the Gelasian Age is the span of time in which the rock strata of the Gelasian Stage was deposited.

2.58 Ma – Gelasian Age/Stage

The Gelasian Age (to 1.8 Ma) is the first of the Pleistocene Ages and equivalent to the Gelasian Stage, which is the rock layer deposited through the Gelasian Age. The Age and Stage are named for a layer found at Monte San Nicola near the ancient city of Gela in Sicily. The Gelasian's base marker – i.e., its Global Stratotype Section and Point (GSSP) – has been placed in rock dated to 2.58 Ma. The Gelasian marks the beginning of glaciation in the northern hemisphere with formation of the first ice sheets (to 1.8 Ma).

Biber/Tegelen and Pre-Illinoian Glacials

The regional names of the first Glacial include Biber (Alpine), Tegelen (Northern Europe) and Pre-Illinoian (North America). Great Britain had potentially three Glacial Stages during the Gelasian but dating is uncertain and they might well have overlapped – known as the Bramertonian Stage, the Baventian Stage and the Pastonian Stage, they are all named after places in East Anglia. In North America, several Glacial Stage names (e.g., Nebraskan, Aftonian, Kansan and Yarmouthian) formerly used have been discredited by recent geological findings. Instead, Pre-Illinoian is used as an umbrella term for all Pleistocene Glacials and Interglacials in North America until 191 ka, the start of the Illinoian Glacial proper.

2.4 Ma – Homo habilis

This was the evolution in sub-Saharan Africa of homo habilis (in Latin, habilis means "capable", in terms of handiwork), the earliest instance of the Homo genus. In evolutionary terms, homo habilis had certain intermediate links between Australopithecus and the later Homo species. The first fossils of homo habilis were found in Tanzania in 1959. The species became extinct 1.5 Ma with evolution into the more advanced homo erectus.

1.8 Ma – Calabrian Age/Stage

Beginning of the Calabrian Age (to 774 ka), second of the Pleistocene Ages and equivalent to the Calabrian Stage. It is named for layers found at Vrica, near Crotone in Calabria, southern Italy.

Donau/Beestonian Glacial

Following a short and perhaps hypothetical Interglacial called the Biber-Donau, the Donau Glacial (Alpine) began. Its British equivalent is the Beestonian Glacial, named for deposits found at Beeston Cliffs, near the village of West Runton in Norfolk. The Donau/Beestonian lasted until about 1 Ma (one million years ago).

1.5 Ma – Homo erectus

Homo erectus, who had a larger brain than homo habilis, used stone tools and was the first hominid to leave Africa with remains found in China, Spain and southern Great Britain.

Evolution of homonids

Hominids to this point had evolved entirely in Africa and all were black. Colour changes took place in those who migrated from Africa and were due to sunlight. Light creates vitamin D in the skin and successive bodies change over several generations to compensate for the vitamin D need. A white skin in Africa lets in too much sunlight, hence a black skin shields the body by reducing light input. In Europe, where there is much less sunlight, the dark skin lets in too little and so becomes lighter. As time passed, Europeans became white and it is significant that Scandinavians are lighter-skinned than Mediterranean peoples. It is reasonable to state that, eventually, the descendants of present-day dark-skinned Europeans and North Americans will be much lighter. Conversely, the descendants of light-skinned people in the tropics will be much darker.

Palaeolithic (Old Stone) Age

The Palaeolithic (Old Stone) Age is believed to have begun 1.5 Ma during the Pleistocene Epoch and was introduced into Europe and Asia by homo erectus. Its main characteristic was the manufacture of tools and weapons using stone rather than wood. The main stone used was flint, chipped into shape. There was no agriculture in the Paleolithic as that is the defining criterion of the Neolithic. The dog was the only domestic animal and humans were either cave-dwelling hunters or herd-trailing nomads who relied heavily on meat for their diet, augmented by whatever roots, berries, etc. could be found, hence the term "hunter-gatherer".

1 Ma – One million years ago

As the Donau/Beestonian Glacial ended, the hypothetical Donau-Günz Interglacial began. It is possible that the retreating glaciers (to 900 ka) enabled homo erectus to spread further into Europe.

900 ka – Günz/Cromerian Glacial

Beginning of the Günz Glacial (Alpine; to 400 ka), known as the Cromerian Glacial (to 478 ka) in Great Britain and Northern Europe. Günz is a river in Bavaria; Cromer is a coastal town in Norfolk.

774 ka – Chibanian Age/Stage

Beginning of the Chibanian Age (to 126 ka), third of the Pleistocene Ages and equivalent to the Chibanian Stage. It is named for strata found at a site in the Chiba Prefecture, on the Pacific coast of Honshu, Japan.

478 ka – Anglian Glacial

Anglian Glacial (to 424 ka) in Great Britain. This glaciation reached the Isles of Scilly, the furthest point south by any ice sheet covering the British Isles.

424 ka – Hoxnian Glacial

Hoxnian Interglacial (to 374 ka) in Great Britain. Named for the village of Hoxne in Suffolk.

400 ka – Günz-Mindel Interglacial

Günz-Mindel Interglacial (Alpine; to 374 ka).

Homo erectus may have learned how to tend spontaneous fire, according to evidence found in Chinese caves.

374 ka – Mindel/Wolstonian Glacial

Mindel Glacial (Alpine; to 300 ka), named after a river in Bavaria. It coincides with the early Wolstonian Glacial (Great Britain; to 130 ka), which is named after the village of Wolston in Warwickshire.

330 ka – Mindel-Riß Interglacial

Mindel-Riß Interglacial (Alpine; to 300 ka).

300 ka – Riß/Wolstonian/Saale Glacial

Riß Glaciation (Alpine; to 130 ka), named after a small river in Baden-Württemberg. It coincides with the end of the Wolstonian and also with the Saale Glaciation (Northern Europe; to 130 ka), which is named after a river in Thuringia.

191 ka – Illinoian Glacial

Illinoian Glacial (North America; to 130 ka). It coincides with the last 61 millennia of the Riß/Wolstonian/Saale.

130 ka – Riß-Würm Interglacial

Riß-Würm Interglacial (Alpine; to 109 ka), also known as the Ipswichian Interglacial in Great Britain, the Eemian Interglacial in Northern Europe and the Sangamon Interglacial in North America. It is the last complete Interglacial in that the Holocene Epoch is technically an Interglacial in its own right, albeit an ongoing one.

126 ka – Late/Upper Pleistocene Age/Stage

Beginning of the Late/Upper Pleistocene Age (to 11.7 ka), fourth and last of the Pleistocene Ages and equivalent to the Late/Upper Pleistocene Stage. These are only provisional designations. They have been agreed by the ICS but await ratification by the IUGS. It has been proposed that the name of the Age/Stage should be Tarantian after the city of Taranto in southern Italy.

109 ka – Würm/Devensian/Weichsel Glacial

Würm Glacial (Alpine; to 14 ka). Named after a river in Bavaria, it is widely known as the "Last Ice Age" and included the Last Glacial Maximum (25 ka to 12.9 ka). The Würm Glacial coincides with the Devensian Glacial in Great Britain and the Weichsel Glaciation in Northern Europe. The Devensian is named after the River Dee (Deva in Latin) in Cheshire. Weichsel is the German name for the River Vistula in Poland. While the Würm/Devensian/Weichsel is often aligned with the Wisconsin Glaciation in North America, the dating and naming conventions there are out of synch with Europe and the Wisconsin per se did not begin until 70 ka.

100 ka (100,000 years ago) – Neanderthals

Development of homo sapiens neanderthalensis (Neanderthals) who lived in Europe and the Middle East till after 40 ka. The Neanderthals had large brains and were typically small and stocky with heavy features including a prominent brow and jaw.

70 ka – Wisconsin Glacial

Official startpoint for the Wisconsin Glacial in North America (to 14 ka).

40 ka – Homo sapiens and Cro-Magnon

Neanderthals died out partly by interbreeding with the earliest types of homo sapiens sapiens, of whom the so-called Cro-Magnon is an example. It was from 40 ka that the Cro-Magnons began moving into Europe from the Near East. Homo sapiens learned how to make fire, probably by creating friction using two pieces of wood.

28 ka – Bering land bridge migrations

First migration of Native Americans across the Bering land bridge from Siberia to Alaska. It is believed that the original tribes subsequently moved down to Central and South America under pressure from later migrations.

25 ka – Last Glacial Maximum

The Last Glacial Maximum (to 12.9 ka) before de-glaciation began in the northern hemisphere. Northern Europe, including most of Great Britain, was covered by an ice sheet. The glaciers had reached the Great Lakes in North America. Sea levels fell and certain key land bridges were temporarily in existence that had significance for human migration: Doggerland (now the southern North Sea and the Dover Strait); the Bering land bridge between Siberia and Alaska; and the land bridges linking Japan to the Asian mainland.

20 ka – Japan and Australia

Rising sea levels in the Pacific Ocean formed the islands of Japan, severing the land bridges with Korea and Siberia. The main islands are Hokkaido, Honshu, Shikoku and Kyushu.

Evidence of human habitation in Australia.

18 ka – Early Cultures

Palaeolithic culture in Egypt.

Cave paintings at Lascaux in the Dordogne. These are mainly of buffalo, deer and other animals hunted by humans. Later paintings occur in caves throughout the world with further examples at Altamira (Spain) and in India, Australia and the Sahara.

14 ka – Late Glacial Interstadial

End of the Würm/Wisconsin Glacial (the "Last Ice Age"). It was followed by the Late Glacial Interstadial (LGI) till 12.9 ka when global temperatures rose significantly and the glaciers began to retreat.

The last migration across the Bering land bridge from Siberia to Alaska. The late-comers are believed to have settled in North America, becoming the Apache, Cheyenne, Comanche, Sioux, etc. Meanwhile, earlier tribes may have reached Tierra del Fuego at the tip of South America.

In an early example of technology, the earliest known harpoons were invented out of reindeer horn by "Magdalenian" hunters in south Europe.

12.9 ka – Younger Dryas

The Younger Dryas (to 11.7 ka) was a temporary but lengthy return to glacial conditions in the northern hemisphere. It is named after an Alpine wildflower called Dryas octopetala, a glacial plant that became abundant at the time. There had been an Older Dryas, which lasted for perhaps 200 years around 14 ka.

11.7 ka – Epochal Boundary

The end of the Younger Dryas marks the boundary between the Pleistocene and Holocene Epochs. At this time, in all parts of the world, humans were still culturally and technologically in the Palaeolithic (Old Stone) Age. Tools and weapons were basic stone or wooden implements. Nomadic tribes followed moving herds. Non-nomadics acquired their food by gathering and hunting.

Retreat of the glaciers

Humans reached the Palaeolithic Age (the Old Stone Age) during the Pleistocene and was ready to ascend to the Neolithic Age (the New Stone Age) after the glaciers retreated at the end of the Last Ice Age around 10 ka. In the Holocene, the main evolutionary characteristic has been the worldwide abundance of homo sapiens sapiens. The Holocene began after the Last Ice Age ended while humans were still in the Palaeolithic but, within the first millennium of the Holocene, tribal communities in the Near East reached the Neolithic level of cultural development by beginning to establish the first agricultural settlements.

Sources

Numerous sources were consulted but many on a temporary basis only. Apologies to the writers I've forgotten but among those which deserve special mention are:

• Encyclopaedia Britannica, various articles.
• Bronowski, Jacob. The Ascent of Man. BBC (1973).
• Fagan, Brian. The Complete Ice Age: How Climate Change Shaped the World. Thames & Hudson (2009).
• Mazur, Allan. Ice Ages: Their Social and Natural History. Cambridge University Press (2022).
• Mithen, Steven. After The Ice. Weidenfeld & Nicolson (2003).