Last Glacial Period

Last Glacial Period
Name	Last Glacial Period
Caption	Artistic depiction of Earth during peak glaciation.
Alt name	Last Ice Age
Time	c. 115,000 – c. 11,700 years BP
Duration	~103,300 years
Glaciation	Quaternary glaciation
Preceded by	Eemian
Followed by	Holocene

Last Glacial Period. The Last Glacial Period, colloquially known as the Last Ice Age, was the most recent major geological epoch within the ongoing Quaternary glaciation. It profoundly reshaped global geography, climate, and ecosystems, reaching its maximum extent approximately 26,500 to 19,000 years ago. This period was characterized by the expansion of massive continental ice sheets and significant global cooling, which directly influenced the evolution and migration patterns of Homo sapiens and other species.

Overview

This interval, formally corresponding to the Marine Isotope Stage 2 through 4, saw the growth of immense ice sheets over North America and Northern Europe. The Laurentide Ice Sheet covered much of Canada and the northern United States, while the Cordilleran Ice Sheet dominated the Pacific Northwest. In Eurasia, the Scandinavian Ice Sheet spread across Great Britain, Scandinavia, and into northwestern Russia. These vast ice masses locked up enormous volumes of water, causing global sea level to drop by approximately 120 meters, exposing continental shelves like Beringia and Sunda Land. The period's end was marked by a rapid climatic transition into the current interglacial, the Holocene.

Timing and subdivisions

The Last Glacial Period began roughly 115,000 years BP, following the warm Eemian interglacial, and concluded with the onset of the Holocene around 11,700 years BP. It is subdivided into earlier and later phases, with the most severe conditions occurring during the Last Glacial Maximum (LGM). The LGM is conventionally dated from about 26,500 to 19,000 years BP, based on evidence from Greenland ice core records like the North Greenland Ice Core Project and marine sediment cores. The preceding millennia are often termed the "glacial build-up," while the terminal phase involved rapid deglaciation and climatic oscillations like the Bølling-Allerød warming and the cold Younger Dryas.

Causes and orbital forcing

The primary driver of the glacial cycle is attributed to variations in Earth's orbit and axial tilt, known as Milankovitch cycles. Specifically, low summer insolation in the northern hemisphere, caused by changes in orbital eccentricity, axial tilt, and precession, prevented seasonal melt of winter snowfall, allowing ice sheets to accumulate. These astronomical forcings were amplified by feedback mechanisms within the climate system, including changes in albedo from expanding ice, reduced atmospheric carbon dioxide concentrations as recorded in Antarctic ice cores like those from Vostok Station, and alterations in ocean circulation patterns such as the Atlantic meridional overturning circulation.

Glacial and interstadial phases

The period was not uniformly cold but was punctuated by several abrupt warming events called interstadials, particularly during the earlier part of the glaciation. These are well-documented in the Greenland ice core chronology as Dansgaard-Oeschger events, which involved rapid warming in the North Atlantic region over decades. Conversely, episodes of extreme cold, known as Heinrich events, occurred when armadas of icebergs calved from the Laurentide Ice Sheet into the North Atlantic, disrupting ocean currents and causing severe Northern Hemisphere cooling. The structure of these events is a key feature of the INTIMATE event stratigraphy.

Environmental conditions and glaciation

Global average temperatures were about 6°C cooler than today, with far greater cooling at high latitudes. Beyond the ice sheets, vast, cold, and dry steppe-tundras like the mammoth steppe dominated much of unglaciated Eurasia and Alaska. Huge proglacial lakes formed at the ice margins, such as Lake Agassiz and Lake Missoula, whose catastrophic outbursts shaped landscapes across the American Midwest. Permafrost extended far south, and lower sea levels created land bridges that connected continents, drastically altering coastlines and enabling biotic exchanges.

Flora and fauna

The flora was dominated by cold-adapted and drought-resistant species. In unglaciated regions, vegetation ranged from polar desert to extensive grasslands and open coniferous forest of Picea and Pinus. The fauna, often termed the Pleistocene megafauna, included iconic species adapted to these harsh conditions, such as the woolly mammoth, woolly rhinoceros, steppe bison, giant ground sloth, and saber-toothed cat. This megafauna was largely distributed across the mammoth steppe biome but faced widespread extinction near the end of the period, an event coinciding with both climatic change and the expansion of Homo sapiens.

Human adaptation and migration

Anatomically modern humans demonstrated remarkable adaptability, developing specialized technologies and social structures to survive. Cultures such as the Gravettian and later Magdalenian in Europe produced sophisticated tools, art, and clothing. The lowered sea levels opened migration routes, facilitating the peopling of the Americas via the Beringia land bridge and the settlement of Sahul (Australia and New Guinea) across the Wallace Line. Key archaeological sites from this era include the Lascaux cave complex in France and the Monte Verde site in Chile, providing evidence of human resilience and expansion during extreme climatic duress.

Category:Quaternary