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| Artist's impression
of Earth during the Last Glacial Maximum. |
Quaternary
Quaternary ( /kwəˈtɜːrnəri, ˈkwɒt.ərˌnɛr.i/
kwə-TUR-nə-ree, KWOT-ər-nerr-ee) is the current and most
recent of the three periods of the Cenozoic Era in the
geologic time scale of the International Commission on
Stratigraphy (ICS). It follows the Neogene Period and
spans from 2.588 ± 0.005 million years ago to the
present. The Quaternary Period is divided into two
epochs: the Pleistocene (2.588 million years ago to 11.7
thousand years ago) and the Holocene (11.7 thousand
years ago to today).[4] The informal term "Late
Quaternary" refers to the past 0.5–1.0 million years.
The Quaternary Period is typically defined by the cyclic
growth and decay of continental ice sheets related to
the Milankovitch cycles and the associated climate and
environmental changes that they caused.
Research history
In 1759 Giovanni Arduino proposed that the geological
strata of northern Italy could be divided into four
successive formations or "orders" (Italian: quattro
ordini). The term "quaternary" was introduced by Jules
Desnoyers in 1829 for sediments of France's Seine Basin
that seemed clearly to be younger than Tertiary Period
rocks.
The Quaternary Period follows the Neogene Period and
extends to the present. The Quaternary covers the time
span of glaciations classified as the Pleistocene, and
includes the present interglacial time-period, the
Holocene.
This places the start of the Quaternary at the onset of
Northern Hemisphere glaciation approximately 2.6 million
years ago. Prior to 2009, the Pleistocene was defined to
be from 1.805 million years ago to the present, so the
current definition of the Pleistocene includes a portion
of what was, prior to 2009, defined as the Pliocene.
Quaternary stratigraphers usually worked with regional
subdivisions. From the 1970s, the International
Commission on Stratigraphy (ICS) tried to make a single
geologic time scale based on GSSP's, which could be used
internationally. The Quaternary subdivisions were
defined based on biostratigraphy instead of paleoclimate.
This led to the problem that the proposed base of the
Pleistocene was at 1.805 Mya, long after the start of
the major glaciations of the northern hemisphere. The
ICS then proposed to abolish use of the name Quaternary
altogether, which appeared unacceptable to the
International Union for Quaternary Research (INQUA).
In 2009, it was decided to make the Quaternary the
youngest period of the Cenozoic Era with its base at
2.588 Mya and including the Gelasian stage, which was
formerly considered part of the Neogene Period and
Pliocene Epoch.
The Anthropocene has been proposed as a third epoch as a
mark of the anthropogenic impact on the global
environment starting with the Industrial Revolution, or
about 200 years ago. The Anthropocene is not officially
designated by the ICS, but a working group has been
working on a proposal for the creation of an epoch or
sub-period. |
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Geology
The 2.6 million years of the Quaternary represents the
time during which recognizable humans existed. Over this
geologically short time period there has been relatively
little change in the distribution of the continents due
to plate tectonics.
The Quaternary geological record is preserved in greater
detail than that for earlier periods.
The major geographical changes during this time period
included the emergence of the Strait of Bosphorus and
Skagerrak during glacial epochs, which respectively
turned the Black Sea and Baltic Sea into fresh water,
followed by their flooding (and return to salt water) by
rising sea level; the periodic filling of the English
Channel, forming a land bridge between Britain and the
European mainland; the periodic closing of the Bering
Strait, forming the land bridge between Asia and North
America; and the periodic flash flooding of Scablands of
the American Northwest by glacial water.
The current extent of Hudson Bay, the Great Lakes and
other major lakes of North America are a consequence of
the Canadian Shield's readjustment since the last ice
age; different shorelines have existed over the course
of Quaternary time. |
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Climate
The climate was one of periodic glaciations with
continental glaciers moving as far from the poles as 40
degrees latitude. There was a major extinction of large
mammals in Northern areas at the end of the Pleistocene
Epoch. Many forms such as saber-toothed cats, mammoths,
mastodons, glyptodonts, etc., became extinct worldwide.
Others, including horses, camels and American cheetahs
became extinct in North America.
Quaternary glaciation
Glaciation took place repeatedly during the Quaternary
Ice Age – a term coined by Schimper in 1839 that began
with the start of the Quaternary about 2.58 Mya and
continues to the present day. |
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Last glacial period
In 1821, a Swiss engineer, Ignaz Venetz, presented an
article in which he suggested the presence of traces of
the passage of a glacier at a considerable distance from
the Alps. This idea was initially disputed by another
Swiss scientist, Louis Agassiz, but when he undertook to
disprove it, he ended up affirming his colleague's
hypothesis. A year later, Agassiz raised the hypothesis
of a great glacial period that would have had
long-reaching general effects. This idea gained him
international fame and led to the establishment of the
Glacial Theory.
In time, thanks to the refinement of geology, it has
been demonstrated that there were several periods of
glacial advance and retreat and that past temperatures
on Earth were very different from today. In particular,
the Milankovitch cycles of Milutin Milankovitch are
based on the premise that variations in incoming solar
radiation are a fundamental factor controlling Earth's
climate.
During this time, substantial glaciers advanced and
retreated over much of North America and Europe, parts
of South America and Asia, and all of Antarctica. The
Great Lakes formed and giant mammals thrived in parts of
North America and Eurasia not covered in ice. These
mammals became extinct when the glacial period Age ended
about 11,700 years ago. Modern humans evolved about
315,000 years ago. During the Quaternary Period,
mammals, flowering plants, and insects dominated the
land. |
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