The Pliocene Epoch is the period in the geologic timescale that extends from
5.333 million to 2.58 million years BP. It is the second and youngest epoch of
the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch
and is followed by the Pleistocene Epoch. Prior to the 2009 revision of the
geologic time scale, which placed the 4 most recent major glaciations entirely
within the Pleistocene, the Pliocene also included the Gelasian stage, which
lasted from 2.588 to 1.806 million years ago, and is now included in the
Pleistocene. As with other older geologic periods,
the geological strata that define the start and end are well identified but
the exact dates of the start and end of the epoch are slightly uncertain. The
boundaries defining the Pliocene are not set at an easily identified worldwide
event but rather at regional boundaries between the warmer Miocene and the
relatively cooler Pliocene. The upper boundary was set at the start of the
Pleistocene glaciations. Etymology
The Pliocene was named by Sir Charles Lyell. The name comes from the Greek
words πλεῖον and καινός and means roughly "continuation of the recent",
referring to the essentially modern marine mollusc faunas. H.W. Fowler
called the term a "regrettable barbarism" and an indication that even
"a good classical scholar" such as Lyell should have requested a philologist's
help when coining words. Subdivisions
In the official timescale of the ICS, the Pliocene is subdivided into two
stages. From youngest to oldest they are:
Piacenzian Zanclean
The Piacenzian is sometimes referred to as the Late Pliocene, whereas the
Zanclean is referred to as the Early Pliocene.
In the system of North American Land Mammal Ages include
Hemphillian, and Blancan. The Blancan extends forward into the Pleistocene.
South American Land Mammal Ages include Montehermosan, Chapadmalalan and Uquian.
In the Paratethys area the Pliocene contains the Dacian and Romanian stages.
As usual in stratigraphy, there are many other regional and local subdivisions in
use. In Britain the Pliocene is divided into
the following stages: Gedgravian, Waltonian, Pre-Ludhamian, Ludhamian,
Thurnian, Bramertonian or Antian, Pre-Pastonian or Baventian, Pastonian
and Beestonian. In the Netherlands the Pliocene is divided into these stages:
Brunssumian C, Reuverian A, Reuverian B, Reuverian C, Praetiglian, Tiglian A,
Tiglian B, Tiglian C1-4b, Tiglian C4c, Tiglian C5, Tiglian C6 and Eburonian.
The exact correlations between these local stages and the ICS stages is still
a matter of detail. Climate
The global average temperature in the mid-Pliocene was 2–3 °C higher than
today, global sea level 25 m higher and the Northern hemisphere ice sheet was
ephemeral before the onset of extensive glaciation over Greenland that occurred
in the late Pliocene around 3 Ma. The formation of an Arctic ice cap is
signaled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in
the North Atlantic and North Pacific ocean beds. Mid-latitude glaciation was
probably underway before the end of the epoch. The global cooling that occurred
during the Pliocene may have spurred on the disappearance of forests and the
spread of grasslands and savannas. Paleogeography
Continents continued to drift, moving from positions possibly as far as 250 km
from their present locations to positions only 70 km from their current
locations. South America became linked to North America through the Isthmus of
Panama during the Pliocene, making possible the Great American Interchange
and bringing a nearly complete end to South America's distinctive large
marsupial predator and native ungulate faunas. The formation of the Isthmus had
major consequences on global temperatures, since warm equatorial
ocean currents were cut off and an Atlantic cooling cycle began, with cold
Arctic and Antarctic waters dropping temperatures in the now-isolated
Atlantic Ocean. Africa's collision with Europe formed
the Mediterranean Sea, cutting off the remnants of the Tethys Ocean. The border
between the Miocene and the Pliocene is also the time of the Messinian salinity
crisis. Sea level changes exposed the
land-bridge between Alaska and Asia. Pliocene marine rocks are well exposed
in the Mediterranean, India, and China. Elsewhere, they are exposed largely near
shores. Flora
The change to a cooler, dry, seasonal climate had considerable impacts on
Pliocene vegetation, reducing tropical species worldwide. Deciduous forests
proliferated, coniferous forests and tundra covered much of the north, and
grasslands spread on all continents. Tropical forests were limited to a tight
band around the equator, and in addition to dry savannahs, deserts appeared in
Asia and Africa. Fauna
Both marine and continental faunas were essentially modern, although continental
faunas were a bit more primitive than today. The first recognizable hominins,
the australopithecines, appeared in the Pliocene.
The land mass collisions meant great migration and mixing of previously
isolated species, such as in the Great American Interchange. Herbivores got
bigger, as did specialized predators. = Mammals=
In North America, rodents, large mastodons and gomphotheres, and opossums
continued successfully, while hoofed animals declined, with camel, deer and
horse all seeing populations recede. Rhinos, three toed horses, oreodonts,
protoceratids, and chalicotheres went extinct. Borophagine dogs and
Agriotherium went extinct, but other carnivores including the weasel family
diversified, and dogs and fast-running hunting bears did well. Ground sloths,
huge glyptodonts, and armadillos came north with the formation of the Isthmus
of Panama. In Eurasia rodents did well, while
primate distribution declined. Elephants, gomphotheres and stegodonts
were successful in Asia, and hyraxes migrated north from Africa. Horse
diversity declined, while tapirs and rhinos did fairly well. Cows and
antelopes were successful, and some camel species crossed into Asia from
North America. Hyenas and early saber-toothed cats appeared, joining
other predators including dogs, bears and weasels.
Africa was dominated by hoofed animals, and primates continued their evolution,
with australopithecines appearing in the late Pliocene. Rodents were successful,
and elephant populations increased. Cows and antelopes continued diversification
and overtaking pigs in numbers of species. Early giraffes appeared, and
camels migrated via Asia from North America. Horses and modern rhinos came
onto the scene. Bears, dogs and weasels joined cats, hyenas and civets as the
African predators, forcing hyenas to adapt as specialized scavengers.
South America was invaded by North American species for the first time
since the Cretaceous, with North American rodents and primates mixing
with southern forms. Litopterns and the notoungulates, South American natives,
were mostly wiped out, except for the macrauchenids and toxodonts, which
managed to survive. Small weasel-like carnivorous mustelids, coatis and short
faced bears migrated from the north. Grazing glyptodonts, browsing giant
ground sloths and smaller caviomorph rodents, pampatheres, and armadillos did
the opposite, migrating to the north and thriving there.
The marsupials remained the dominant Australian mammals, with herbivore forms
including wombats and kangaroos, and the huge diprotodon. Carnivorous marsupials
continued hunting in the Pliocene, including dasyurids, the dog-like
thylacine and cat-like Thylacoleo. The first rodents arrived in Australia. The
modern platypus, a monotreme, appeared. = Birds=
The predatory South American phorusrhacids were rare in this time;
among the last was Titanis, a large phorusrhacid that migrated to North
America and rivaled mammals as top predator. Other birds probably evolved
at this time, some modern, some now extinct.
= Reptiles and amphibians= Alligators and crocodiles died out in
Europe as the climate cooled. Venomous snake genera continued to increase as
more rodents and birds evolved. Rattlesnakes first appeared in the
Pliocene. The modern species Alligator mississippiensis, having evolved in the
Miocene, continued into the Pliocene, except with a more northern range;
specimens have been found in very late Miocene deposits of Tennessee. Giant
tortoises still thrived in North America, with genera like
Hesperotestudo. Madtsoid snakes were still present in Australia. The
amphibian order Allocaudata went extinct.
Oceans Oceans continued to be relatively warm
during the Pliocene, though they continued cooling. The Arctic ice cap
formed, drying the climate and increasing cool shallow currents in the
North Atlantic. Deep cold currents flowed from the Antarctic.
The formation of the Isthmus of Panama about 3.5 million years ago cut off the
final remnant of what was once essentially a circum-equatorial current
that had existed since the Cretaceous and the early Cenozoic. This may have
contributed to further cooling of the oceans worldwide.
The Pliocene seas were alive with sea cows, seals and sea lions.
Supernovae In 2002, Narciso Benítez et al.
calculated that roughly 2 million years ago, around the end of the Pliocene
epoch, a group of bright O and B stars called the Scorpius-Centaurus OB
association passed within 130 light-years of Earth and that one or
more supernova explosions gave rise to a feature known as the Local Bubble. Such
a close explosion could have damaged the Earth's ozone layer and caused the
extinction of some ocean life. See also
List of fossil sites References
Further reading Comins, Niel F.; William J. Kaufmann
III. Discovering the Universe. New York, NY: Susan Finnemore Brennan. ISBN
0-7167-7584-0. Gradstein, F.M.; Ogg, J.G. & Smith,
A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
Ogg, Jim. "Overview of Global Boundary Stratotype Sections and Points".
Retrieved 2006-04-30. Van Andel, Tjeerd H.. New Views on an
Old Planet: a History of Global Change. Cambridge: Cambridge University Press.
ISBN 0-521-44243-5. External links
Mid-Pliocene Global Warming: NASA/GISS Climate Modeling
Palaeos Pliocene PBS Change: Deep Time: Pliocene
Possible Pliocene supernova "Supernova dealt deaths on Earth?
Stellar blasts may have killed ancient marine life" Science News Online
retrieved February 2, 2002 UCMP Berkeley Pliocene Epoch Page
Pliocene Microfossils: 100+ images of Pliocene Foraminifera