6.3 Quaternary period

The Quaternary period, spanning from 2.58 million years ago to today, is marked by repeated glacial-interglacial cycles and human evolution. This era saw major climate shifts, causing ice sheets to grow and shrink, sea levels to fluctuate, and ecosystems to transform dramatically.

During the Pleistocene epoch, massive ice sheets covered much of the Northern Hemisphere. The Holocene, our current warm period, began 11,700 years ago. This stable climate allowed human civilizations to flourish and agriculture to expand globally.

Quaternary period overview

• The Quaternary period is the most recent geological period, spanning from 2.58 million years ago to the present day, and is characterized by repeated glacial-interglacial cycles and the evolution and dispersal of humans
• Quaternary environments and ecosystems were strongly influenced by climatic fluctuations, with the growth and decay of continental ice sheets leading to major changes in sea level, temperature, and precipitation patterns
• The Quaternary period is divided into two epochs: the Pleistocene (2.58 million to 11,700 years ago) and the Holocene (11,700 years ago to the present)

Pleistocene and Holocene epochs

Top images from around the web for Pleistocene and Holocene epochs

• 

  Pleistocene - Wikipedia View original

  Is this image relevant?

• 

  Methods and problems in historical climatology View original

  Is this image relevant?

• 

  16.1 Glacial Periods in Earth’s History | Physical Geology View original

  Is this image relevant?

• 

  Pleistocene - Wikipedia View original

  Is this image relevant?

• 

  Methods and problems in historical climatology View original

  Is this image relevant?

1 of 3

Top images from around the web for Pleistocene and Holocene epochs

• 

  Pleistocene - Wikipedia View original

  Is this image relevant?

• 

  Methods and problems in historical climatology View original

  Is this image relevant?

• 

  16.1 Glacial Periods in Earth’s History | Physical Geology View original

  Is this image relevant?

• 

  Pleistocene - Wikipedia View original

  Is this image relevant?

• 

  Methods and problems in historical climatology View original

  Is this image relevant?

1 of 3

• The Pleistocene epoch was marked by repeated glacial-interglacial cycles, with ice sheets advancing and retreating in response to changes in Earth's orbital parameters and atmospheric greenhouse gas concentrations
• The Holocene epoch began at the end of the last glacial period and is characterized by a relatively stable, warm climate that has allowed for the development of human civilizations and the expansion of agriculture
• The transition from the Pleistocene to the Holocene is marked by the onset of the current interglacial period, known as the Holocene climatic optimum, which occurred around 9,000 to 5,000 years ago

Pleistocene glaciations

• The Pleistocene epoch was characterized by repeated glacial-interglacial cycles, with ice sheets advancing and retreating over large portions of the Northern Hemisphere
• These glacial cycles were driven by a combination of factors, including changes in Earth's orbital parameters (Milankovitch cycles), variations in atmospheric greenhouse gas concentrations, and feedback mechanisms involving the oceans, atmosphere, and cryosphere

Causes of glacial-interglacial cycles

• Milankovitch cycles, which include variations in Earth's eccentricity, obliquity, and precession, alter the amount and distribution of solar radiation reaching the Earth's surface, leading to changes in global temperature and ice sheet growth
• Variations in atmospheric greenhouse gas concentrations, particularly carbon dioxide (CO2) and methane (CH4), amplify the effects of orbital forcing by altering the Earth's radiative balance
• Positive feedback mechanisms, such as the ice-albedo feedback and the CO2 feedback, can amplify the initial cooling or warming triggered by orbital forcing and greenhouse gas changes

Major ice ages and glacial extents

• The Pleistocene epoch saw several major glacial advances, including the Nebraskan (2.58-1.8 million years ago), Kansan (1.5-0.8 million years ago), Illinoian (300,000-130,000 years ago), and Wisconsinan (110,000-11,700 years ago) glaciations in North America
• During glacial maxima, ice sheets covered much of Canada, the northern United States, and northern Europe, with smaller ice caps and mountain glaciers present in other regions (Patagonia, the Himalayas, and the Alps)
• The last glacial maximum (LGM) occurred around 26,500-19,000 years ago, with ice sheets reaching their maximum extent and global sea levels dropping by 120-135 meters

Effects on sea levels and climate

• The growth and decay of continental ice sheets during the Pleistocene had a profound impact on global sea levels, with sea levels falling during glacial periods and rising during interglacial periods
• Glacial periods were characterized by cooler, drier climates, with the expansion of tundra and steppe environments and the contraction of forests and tropical rainforests
• Interglacial periods, such as the current Holocene epoch, were marked by warmer, wetter climates, with the expansion of forests and the retreat of tundra and steppe environments

Pleistocene megafauna

• The Pleistocene epoch was characterized by the presence of large, iconic mammals known as megafauna, which included species such as mammoths, mastodons, giant ground sloths, and saber-toothed cats
• These megafaunal species were adapted to the cooler, drier climates and open habitats of the Pleistocene, and many of them went extinct during the late Pleistocene and early Holocene

Giant mammals of the Pleistocene

• Mammoths and mastodons were large, elephant-like mammals that inhabited the tundra and steppe environments of the Pleistocene, with species such as the woolly mammoth (Mammuthus primigenius) and the American mastodon (Mammut americanum) being among the most well-known
• Giant ground sloths, such as the Megatherium and Eremotherium, were large, herbivorous mammals that inhabited the Americas during the Pleistocene, with some species reaching weights of up to 4 tons
• Saber-toothed cats, such as Smilodon and Homotherium, were large, predatory mammals characterized by their elongated, saber-like canine teeth, which they used to hunt megafaunal prey

Megafaunal extinctions

• The late Pleistocene and early Holocene saw a wave of megafaunal extinctions, with many large mammal species disappearing from the fossil record
• In North America, around 45 out of 61 megafaunal genera went extinct between 13,000 and 11,000 years ago, including all species of mammoths, mastodons, giant ground sloths, and saber-toothed cats
• Similar extinctions occurred in other regions, such as South America, Australia, and Eurasia, although the timing and extent of these extinctions varied

Role of human hunting vs climate change

• The causes of the Pleistocene megafaunal extinctions have been the subject of much debate, with two main hypotheses proposed: human hunting and climate change
• The overkill hypothesis suggests that human hunting, particularly by early Paleoindian cultures in the Americas, was the primary driver of megafaunal extinctions, with humans exploiting naive prey populations that had not evolved defenses against human predation
• The climate change hypothesis proposes that the rapid climatic and environmental changes associated with the end of the last glacial period, including rising temperatures, changing precipitation patterns, and the expansion of forests, led to the decline and extinction of megafaunal species that were adapted to cooler, more open habitats
• Recent research suggests that a combination of human hunting and climate change likely contributed to the Pleistocene megafaunal extinctions, with the relative importance of each factor varying depending on the region and the species involved

Human evolution in the Quaternary

• The Quaternary period saw the emergence and evolution of the genus Homo, with several species of early humans and archaic hominins inhabiting Africa, Eurasia, and Southeast Asia during the Pleistocene
• The Quaternary also witnessed the development of key human adaptations, such as bipedalism, tool use, and the control of fire, as well as the dispersal of early human populations out of Africa and into other regions of the world

Homo erectus and early human migrations

• Homo erectus was a species of early human that first appeared in Africa around 1.9 million years ago and later spread to Eurasia, representing the first major dispersal of early humans out of Africa
• H. erectus was characterized by a larger brain size, more advanced stone tool technology (Acheulean handaxes), and a more human-like body proportions compared to earlier hominins (Australopithecus and early Homo)
• H. erectus populations in Eurasia, such as those represented by the Peking Man and Java Man fossils, persisted until around 143,000 years ago in Indonesia and 550,000 years ago in China, overlapping with later hominin species such as Homo heidelbergensis and Homo sapiens

Neanderthals and Denisovans

• Neanderthals (Homo neanderthalensis) were a species of archaic human that inhabited Europe and western Asia from around 400,000 to 40,000 years ago, coexisting with anatomically modern humans (Homo sapiens) for part of this time
• Neanderthals were adapted to the cold climates of Pleistocene Europe, with a stocky build, large nose, and a more robust skeleton compared to modern humans, and they produced advanced stone tools (Mousterian technology) and engaged in complex behaviors such as burial of the dead and the use of pigments
• Denisovans were another species of archaic human that inhabited Asia during the Pleistocene, known primarily from genetic evidence and a few fossil fragments from Denisova Cave in Siberia and Baishiya Karst Cave in Tibet
• Both Neanderthals and Denisovans interbred with anatomically modern humans, leaving a genetic legacy in the genomes of present-day human populations (1-4% Neanderthal ancestry in Eurasians and 4-6% Denisovan ancestry in Melanesians and Aboriginal Australians)

Emergence of anatomically modern humans

• Anatomically modern humans (Homo sapiens) first appeared in Africa around 300,000 years ago, as evidenced by fossil remains from Jebel Irhoud in Morocco and Omo Kibish in Ethiopia
• Modern humans later spread out of Africa in multiple waves, with the first major dispersal occurring around 70,000-60,000 years ago and reaching Australia by 65,000-50,000 years ago and Europe by 45,000-40,000 years ago
• The emergence of modern human behavior, characterized by the use of symbolic objects (shell beads, pigments), the production of figurative art (cave paintings, figurines), and the development of more advanced technologies (bone tools, projectile weapons), occurred gradually during the Late Pleistocene, with the earliest evidence dating to around 100,000-70,000 years ago in Africa

Quaternary environments and ecosystems

• Quaternary environments and ecosystems were strongly influenced by the repeated glacial-interglacial cycles of the Pleistocene, with the growth and decay of continental ice sheets leading to major changes in sea level, temperature, and precipitation patterns
• The Pleistocene saw the expansion of cold-adapted biomes, such as tundra and steppe, during glacial periods, and the contraction of these biomes and the expansion of forests during interglacial periods

Tundra and ice sheet biomes

• Tundra environments, characterized by low-growing vegetation (mosses, lichens, sedges) and permafrost soils, expanded during glacial periods in regions adjacent to continental ice sheets, such as in northern Eurasia and North America
• Ice sheet biomes, found on the surface of continental ice sheets and glaciers, supported microbial communities and some invertebrates adapted to extreme cold and low nutrient availability (ice worms, snow algae)
• The Pleistocene tundra and ice sheet biomes were inhabited by cold-adapted megafauna, such as woolly mammoths, woolly rhinos, and reindeer, as well as smaller mammals like arctic foxes and lemmings

Pleistocene steppe and savanna habitats

• Steppe environments, characterized by grasslands and scattered shrubs, expanded during glacial periods in regions with cold, dry climates, such as central Eurasia and the interior of North America
• Pleistocene steppe habitats supported a diverse assemblage of grazing megafauna, including horses, bison, and mammoths, as well as predators such as wolves and lions
• Savanna environments, characterized by a mix of grasslands and scattered trees, expanded in regions with warmer, wetter climates during interglacial periods, such as in Africa and South Asia
• Pleistocene savanna habitats were inhabited by a range of megafaunal species, including elephants, giraffes, and large predators like sabertooth cats and hyenas

Refugia and post-glacial recolonization

• During glacial periods, many temperate and boreal species retreated to refugia, isolated areas with more favorable climatic conditions that allowed these species to persist through the glacial period
• Refugia for temperate species during the last glacial period included the Iberian, Italian, and Balkan peninsulas in Europe, and the Appalachian Mountains and Gulf Coast in North America
• As the climate warmed during the transition to the Holocene, species expanded out of these refugia and recolonized previously glaciated regions, leading to the establishment of modern biomes and species distributions
• The study of post-glacial recolonization patterns using genetic data and fossil records has provided insights into the biogeographic history and evolutionary dynamics of many species, including trees (oaks, beeches), mammals (brown bears, red deer), and birds (great tits, European robins)

Quaternary geology and landforms

• The Quaternary period saw the formation of distinctive landforms and sedimentary deposits associated with glacial processes, wind erosion and deposition, and volcanic and tectonic activity
• The study of Quaternary geology and landforms provides insights into past climatic conditions, landscape evolution, and the geomorphic processes that have shaped the Earth's surface

Glacial deposits and landforms

• Glacial deposits, such as till (unsorted sediment deposited directly by glacial ice), moraines (ridges of till deposited at the margins of glaciers), and outwash (sorted sediment deposited by glacial meltwater), are widespread in regions that were covered by ice sheets during the Pleistocene
• Glacial erosion also created distinctive landforms, such as U-shaped valleys, cirques, arêtes, and fjords, which are common in mountainous regions and high-latitude landscapes
• The study of glacial deposits and landforms, particularly the distribution and age of moraines, has been used to reconstruct the extent and timing of past glaciations and to infer past climatic conditions

Loess deposits and windblown sediments

• Loess is a type of windblown sediment composed of silt-sized particles that accumulates in regions downwind of major dust sources, such as glacial outwash plains and deserts
• Extensive loess deposits formed during the Pleistocene in regions such as central China, central Europe, and the North American Midwest, often reaching thicknesses of tens to hundreds of meters
• Loess deposits contain valuable records of past climatic conditions, as the accumulation of loess is often associated with cold, dry climates and the expansion of dust source areas during glacial periods
• Other windblown sediments, such as sand dunes and sand sheets, also formed during the Quaternary in regions with arid or semi-arid climates, such as the Sahara, Arabian, and Kalahari deserts

Quaternary volcanism and tectonics

• The Quaternary period saw ongoing volcanic and tectonic activity in many regions of the world, including the formation of new volcanic islands (Surtsey, Iceland), the eruption of large volcanic centers (Yellowstone, USA; Toba, Indonesia), and the occurrence of major earthquakes along plate boundaries (San Andreas Fault, USA; Alpine Fault, New Zealand)
• Volcanic eruptions during the Quaternary have had significant impacts on climate and ecosystems, with large eruptions leading to short-term cooling (due to the injection of sulfate aerosols into the stratosphere) and the disruption of regional to global ecosystems
• Tectonic activity during the Quaternary, such as the uplift of mountain ranges (Himalayas, Andes) and the opening of rifts (East African Rift), has influenced regional climates, drainage patterns, and the distribution of species and ecosystems
• The study of Quaternary volcanic and tectonic activity, using methods such as tephrochronology (dating of volcanic ash layers) and paleoseismology (study of past earthquakes), has provided insights into the frequency and magnitude of these events and their potential impacts on human societies and the environment

Quaternary climate and paleoclimatology

• The Quaternary period is characterized by major climatic fluctuations, particularly the repeated glacial-interglacial cycles of the Pleistocene, which were driven by a combination of orbital forcing, greenhouse gas variations, and feedback mechanisms
• Paleoclimatology, the study of past climates using various proxy records, has provided detailed insights into the patterns, causes, and impacts of Quaternary climate change

Ice core records and paleoclimate proxies

• Ice cores from polar ice sheets (Greenland, Antarctica) and mountain glaciers provide high-resolution records of past climatic conditions, including temperature, precipitation, and atmospheric composition, spanning hundreds of thousands of years
• Ice cores contain bubbles of ancient air, which can be analyzed to reconstruct past atmospheric greenhouse gas concentrations (CO2, CH4), as well as dust and aerosol content
• Other paleoclimate proxies, such as marine sediments (foraminifera shells, alkenones), lake sediments (pollen, diatoms), and speleothems (cave deposits), provide complementary records of past climatic conditions and environmental changes at regional to global scales

Abrupt climate change events

• The Quaternary period saw several abrupt climate change events, characterized by rapid shifts in temperature, precipitation, and atmospheric and oceanic circulation patterns, often occurring within decades to centuries
• Examples of abrupt climate change events include Dansgaard-Oeschger events (rapid warmings followed by gradual coolings, occurring during glacial periods), Heinrich events (massive discharges of icebergs into the North Atlantic, associated with cold periods), and the Younger Dryas (a cold reversal during the last deglaciation, 12,900-11,700 years ago)
• These abrupt climate change events are thought to be related to instabilities in the Earth's climate system