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| Holocene temperature
variations. |
Holocene
The Holocene ( /ˈhɒl.əˌsiːn, ˈhɒl.oʊ-, ˈhoʊ.lə-, ˈhoʊ.loʊ-/
HOL-ə-seen, HOL-oh-, HOH-lə-, HOH-loh-) is the current
geological epoch. It began approximately 11,650 cal
years before present, after the last glacial period,
which concluded with the Holocene glacial retreat. The
Holocene and the preceding Pleistocene together form the
Quaternary period. The Holocene has been identified with
the current warm period, known as MIS 1. It is
considered by some to be an interglacial period within
the Pleistocene Epoch, called the Flandrian
interglacial.
The Holocene corresponds with the rapid proliferation,
growth and impacts of the human species worldwide,
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. In July 2018, the International Union of
Geological Sciences split the Holocene epoch into three
distinct subsections, Greenlandian (11,700 years ago to
8,200 years ago), Northgrippian (8,200 years ago to
4,200 years ago) and Meghalayan (4,200 years ago to the
present), as proposed by International Commission on
Stratigraphy. The boundary stratotype of the Meghalayan
is a speleothem in Mawmluh cave in India, and the global
auxiliary stratotype is an ice core from Mount Logan in
Canada.
Etymology
The word is formed from two Ancient Greek words. Holos
(ὅλος) is the Greek word for "whole". "Cene" comes from
the Greek word kainos (καινός), meaning "new". The
concept is that this epoch is "entirely new". The suffix
'-cene' is used for all the seven epochs of the Cenozoic
Era. |
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Overview
It is accepted by the International Commission on
Stratigraphy that the Holocene started approximately
11,650 cal years BP. The Subcommission on Quaternary
Stratigraphy deprecates the term 'Recent' as an
alternative to Holocene; it also observes that the term
Flandrian, derived from marine transgression sediments
on the Flanders coast of Belgium, has been used as a
synonym for Holocene by authors who consider the last
10,000 years should have the same stage-status as
previous interglacial events and thus be included in the
Pleistocene. The International Commission on
Stratigraphy, however, considers the Holocene an epoch
following the Pleistocene and specifically 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 (10 ka–9 ka BP),
- Boreal (9 ka–8 ka BP),
- Atlantic (8 ka–5 ka BP),
- Subboreal (5 ka–2.5 ka BP) and
- Subatlantic (2.5 ka BP–present).
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Note: "ka BP" means "kilo-annum Before Present", i.e. 1,000
years before 1950 (non-calibrated C14 dates) |
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Geology
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 35 m (115
ft) in the early 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 180 m (590 ft) 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. Holocene marine fossils are known, for
example, from 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.[citation needed]
Post-glacial rebound in the Scandinavia region resulted
in the formation of the Baltic Sea. Earthquakes are a
leading cause of sediment deformation, leading to the
creation and destruction of bodies of water. The region
continues to rise, still causing weak earthquakes across
Northern Europe. The equivalent event in North America
was the rebound of Hudson Bay, as it shrank from its
larger, immediate post-glacial Tyrrell Sea phase, to
near its present boundaries.
Climate
Compared to the preceding cold period (Glaciation),
climate has been relatively stable over the Holocene.
Ice core records show that before the Holocene there was
global warming after the end of the last ice age and
cooling periods, but climate changes became more
regional at the start of the Younger Dryas. 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 Holocene climatic optimum (HCO) was a period of
warming in which the global climate became warmer.
However, the warming was probably not uniform across the
world. This period of warmth ended about 5,500 years ago
with the descent into the Neoglacial and concomitant
Neopluvial. At that time, the climate was not unlike
today's, but there was a slightly warmer period from the
10th–14th centuries known as the Medieval Warm Period.
This was followed by the Little Ice Age, from the 13th
or 14th century to the mid-19th century.
The temporal and spatial extent of Holocene climate
change 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 (Bond events) 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. |
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Ecological developments
Animal and plant life have not evolved much during the
relatively short Holocene, but there have been major
shifts in the distributions of plants and animals. A
number of large animals including mammoths and
mastodons, saber-toothed cats like Smilodon and
Homotherium, and giant sloths disappeared in the late
Pleistocene and early Holocene—especially in North
America, where animals that survived elsewhere
(including horses and camels) became extinct. This
extinction of American megafauna has been blamed by some
on the Clovis people, who vanished at the same time,
though climatic change or a bolide impact are favored by
others.
Throughout the world, ecosystems in cooler climates that
were previously regional have been isolated in higher
altitude ecological "islands".
The 8.2-ka event, an abrupt cold spell recorded as a
negative excursion in the δ18O record lasting 400 years,
is the most prominent climatic event occurring in the
Holocene epoch, and may have marked a resurgence of ice
cover. It has been suggested that this event was caused
by the final drainage of Lake Agassiz, which had been
confined by the glaciers, disrupting the thermohaline
circulation of the Atlantic. Subsequent research,
however, suggested that the discharge was probably
superimposed upon a longer episode of cooler climate
lasting up to 600 years and observed that the extent of
the area affected was unclear.
Human developments
The beginning of the Holocene corresponds with the
beginning of the Mesolithic age in most of Europe, but
in regions such as the Middle East and Anatolia with a
very early neolithisation, Epipaleolithic is preferred
in place of Mesolithic. Cultures in this period include
Hamburgian, Federmesser, and the Natufian culture,
during which the oldest inhabited places still existing
on Earth were first settled, such as Tell es-Sultan
(Jericho) in the Middle East. There is also evolving
archeological evidence of proto-religion at locations
such as Göbekli Tepe, as long ago as the 9th millennium
BCE.
Both are followed by the aceramic Neolithic (Pre-Pottery
Neolithic A and Pre-Pottery Neolithic B) and the pottery
Neolithic. The Late Holocene brought advancements such
as the bow and arrow and saw new methods of warfare in
North America. Spear throwers and their large points
were replaced by the bow and arrow with its small narrow
points beginning in Oregon and Washington. Villages
built on defensive bluffs indicate increased warfare,
leading to food gathering in communal groups for
protection rather than individual hunting. |
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 Kiddle: Holocene
Wikipedia: Holocene |
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