Holocene
The Holocene is the current geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene together form the Quaternary period. The Holocene is an interglacial period within the ongoing glacial cycles of the Quaternary, and is equivalent to Marine Isotope Stage 1. The name "Holocene" comes from Ancient Greek ὅλος, meaning "whole", and καινός, meaning "new, recent", referring that this epoch is "entirely new".
The Holocene correlates with the last maximum axial tilt towards the Sun of the Earth's obliquity. The Holocene corresponds with the rapid proliferation, growth, and impacts of the human species worldwide, hence the Holocene is often commonly referred to as the Age of Humans, including all of its written history, technological revolutions, development of major civilizations, and overall significant transition towards urban living in the present. The human impact on modern-era Earth and its ecosystems may be considered of global significance for the future evolution of living species, including approximately synchronous lithospheric evidence, or more recently hydrospheric and atmospheric evidence of the human impact.
Following the extinction of most large terrestrial mammals outside of Africa during the preceding Late Pleistocene, the ecosystems of the Holocene continued to be impacted by extinctions, largely of human causation.
In July 2018, the International Union of Geological Sciences split the Holocene Epoch into three distinct ages based on the climate, Greenlandian, Northgrippian and Meghalayan, as proposed by the International Commission on Stratigraphy. The oldest age, the Greenlandian, was characterized by a warming following the preceding ice age. The Northgrippian Age is known for vast cooling due to a disruption in ocean circulations that was caused by the melting of glaciers. The most recent age of the Holocene is the present Meghalayan, which began with extreme drought that lasted around 200 years.
Etymology
The word "Holocene" comes from Ancient Greek ὅλος, meaning "whole", and καινός, meaning "new, recent", referring that this epoch is "entirely new". The suffix '-cene' is used for all the seven epochs of the Cenozoic Era.Overview
The International Commission on Stratigraphy has defined the Holocene as starting approximately 11,700 years before 2000 CE. The Subcommission on Quaternary Stratigraphy regards the term 'recent' as an incorrect way of referring to the Holocene, preferring the term 'modern' instead to describe current processes. It also observes that the term 'Flandrian' may be used as a synonym for Holocene, although it is becoming outdated. The International Commission on Stratigraphy, however, considers the Holocene to be an epoch following the Pleistocene and specifically following the last glacial period. Local names for the last glacial period include the Wisconsinan in North America, the Weichselian in Europe, the Devensian in Britain, the Llanquihue in Chile and the Otiran in New Zealand.The Holocene can be subdivided into five time intervals, or chronozones, based on climatic fluctuations:
- Preboreal,
- Boreal,
- Atlantic,
- Subboreal and
- Subatlantic.
Paleontologists have not defined any faunal stages for the Holocene. If subdivision is necessary, periods of human technological development, such as the Mesolithic, Neolithic, and Bronze Age, are usually used. However, the time periods referenced by these terms vary with the emergence of those technologies in different parts of the world.
Some scholars have argued that a third epoch of the Quaternary, the Anthropocene, has now begun. This term has been used to denote the present time-interval in which many geologically significant conditions and processes have been profoundly altered by human activities. The 'Anthropocene' was never a formally defined geological unit. The Subcommission on Quaternary Stratigraphy of the International Commission on Stratigraphy had a working group to determine whether it should be. In May 2019, members of the working group voted in favour of recognizing the Anthropocene as formal chrono-stratigraphic unit, with stratigraphic signals around the mid-twentieth century CE as its base. The exact criteria were still to be determined, after which the recommendation also had to be approved by the working group's parent bodies. In March 2024, after 15 years of deliberation, the Anthropocene Epoch proposal of the working group was voted down by a wide margin by the SQS, owing largely to its shallow sedimentary record and extremely recent proposed start date. The ICS and the International Union of Geological Sciences later formally confirmed, by a near unanimous vote, the rejection of the working group's Anthropocene Epoch proposal for inclusion in the Geologic Time Scale.
Geology
The Holocene is a geologic epoch that follows directly after the Pleistocene. Continental motions due to plate tectonics are less than a kilometre over a span of only 10,000 years. However, ice melt caused world sea levels to rise about in the early part of the Holocene and another 30 m in the later part of the Holocene. In addition, many areas above about 40 degrees north latitude had been depressed by the weight of the Pleistocene glaciers and rose as much as due to post-glacial rebound over the late Pleistocene and Holocene, and are still rising today.The sea-level rise and temporary land depression allowed temporary marine incursions into areas that are now far from the sea. For example, marine fossils from the Holocene epoch have been found in locations such as Vermont and Michigan. Other than higher-latitude temporary marine incursions associated with glacial depression, Holocene fossils are found primarily in lakebed, floodplain, and cave deposits. Holocene marine deposits along low-latitude coastlines are rare because the rise in sea levels during the period exceeds any likely tectonic uplift of non-glacial origin.
Post-glacial rebound in the Scandinavia region resulted in a shrinking Baltic Sea. The region continues to rise, still causing weak earthquakes across Northern Europe. An equivalent event in North America was the rebound of Hudson Bay, as it shrank from its larger, immediate post-glacial Tyrrell Sea phase, to its present boundaries.
Climate
The climate throughout the Holocene has shown significant variability despite ice core records from Greenland suggesting a more stable climate following the preceding ice age. Marine chemical fluxes during the Holocene were lower than during the Younger Dryas, but were still considerable enough to imply notable changes in the climate.The temporal and spatial extent of climate change during the Holocene is an area of considerable uncertainty, with radiative forcing recently proposed to be the origin of cycles identified in the North Atlantic region. Climate cyclicity through the Holocene has been observed in or near marine settings and is strongly controlled by glacial input to the North Atlantic. Periodicities of ≈2500, ≈1500, and ≈1000 years are generally observed in the North Atlantic. At the same time spectral analyses of the continental record, which is remote from oceanic influence, reveal persistent periodicities of 1,000 and 500 years that may correspond to solar activity variations during the Holocene Epoch. A 1,500-year cycle corresponding to the North Atlantic oceanic circulation may have had widespread global distribution in the Late Holocene. From 8,500 BP to 6,700 BP, North Atlantic climate oscillations were highly irregular and erratic because of perturbations from substantial ice discharge into the ocean from the collapsing Laurentide Ice Sheet. The Greenland ice core records indicate that climate changes became more regional and had a larger effect on the mid-to-low latitudes and mid-to-high latitudes after ~5600 B.P.
Human activity through land use changes already by the Mesolithic had major ecological impacts; it was an important influence on Holocene climatic changes, and is believed to be why the Holocene is an atypical interglacial that has not experienced significant cooling over its course. From the start of the Industrial Revolution onwards, large-scale anthropogenic greenhouse gas emissions caused the Earth to warm. Likewise, climatic changes have induced substantial changes in human civilisation over the course of the Holocene.
During the transition from the last glacial to the Holocene, the Huelmo–Mascardi Cold Reversal in the Southern Hemisphere began before the Younger Dryas, and the maximum warmth flowed south to north from 11,000 to 7,000 years ago. It appears that this was influenced by the residual glacial ice remaining in the Northern Hemisphere until the later date. The first major phase of Holocene climate was the Preboreal. At the start of the Preboreal occurred the Preboreal Oscillation. The Holocene Climatic Optimum was a period of warming throughout the globe but was not globally synchronous and uniform. Following the HCO, the global climate entered a broad trend of very gradual cooling known as Neoglaciation, which lasted from the end of the HCO to before the Industrial Revolution. From the 10th-14th century, the climate was similar to that of modern times during a period known as the Mediaeval Warm Period, also known as the Mediaeval Climatic Optimum. It was found that the warming that is taking place in current years is both more frequent and more spatially homogeneous than what was experienced during the MWP. A warming of +1 degree Celsius occurs 5–40 times more frequently in modern years than during the MWP. The major forcing during the MWP was due to greater solar activity, which led to heterogeneity compared to the greenhouse gas forcing of modern years that leads to more homogeneous warming. This was followed by the Little Ice Age from the 13th or 14th century to the mid-19th century. The LIA was the coldest interval of time of the past two millennia. Following the Industrial Revolution, warm decadal intervals became more common relative to before as a consequence of anthropogenic greenhouse gases, resulting in progressive global warming. In the late 20th century, anthropogenic forcing superseded variations in solar activity as the dominant driver of climate change, though solar activity has continued to play a role.