Information About ™Pliocene |
| CATEGORIES ABOUT PLIOCENE | |
| pliocenepliocene | |
| neogene | |
|
The Pliocene is the second epoch of the Neogene period of the Cenozoic Era . The Pliocene follows the Miocene epoch and is followed by the Pleistocene epoch. The Pliocene was named by Sir Charles Lyell . The name comes from the Greek words ''pleion'' (more) and ''ceno'' (new) and means roughly "continuation of the recent" and refers to the essentially modern marine Mollusc faunas. 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 onset of 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 intended to be set at the start of the Pleistocene glaciations but is now considered to be set too late. Many geologists find the broader divisions into Paleogene and Neogene more useful. Astronomers suspect that a massive Supernova occurred relatively near the Earth and might have caused a significant breakdown of the Ozone Layer and the extinction of some ocean life. PLIOCENE SUBDIVISIONS The Pliocene Faunal Stage s from youngest to oldest are: PLIOCENE CLIMATE Climates became cooler and drier, and seasonal, similar to modern climates. Antarctica became ice-bound, entirely covered with year-round glaciation, near or before the start of the Pliocene. The formation of an Arctic ice cap ''ca'' 3 mya is signalled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in the North Atlantic and North Pacific ocean beds (Van Andel 1994 p 226). Mid-latitude Glaciation were probably underway before the end of the epoch. PLIOCENE PALEOGEOGRAPHY Continents continued to Drift toward their present positions, moving from positions possibly as far as 250km 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, bringing a nearly complete end to South America's distinctive Marsupial faunas. The formation of the Isthmus had major consequences on global temperatures, as 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 . 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. PLIOCENE FLORA The change to a cooler, dry, seasonal climate had considerable impacts on Pliocene vegetation, reducing tropical species world-wide. Deciduous forests proliferated, Coniferous forests and Tundra covered much of the north, and Grassland s spread on all continents (except Antarctica). Tropical forests were limited to a tight band around the equator, and in addition to dry Savannahs , Deserts appeared in Asia and Africa. PLIOCENE FAUNA , Florida (EEUU)]] Both marine and continental faunas were essentially modern, although continental faunas were recognizably a bit more primitive than today. The first recognizable Hominin s, the Australopithecine s, appeared in the Pliocene. The land mass collisions meant great migration and mixing of previously isolated species. Herbivores got bigger, as did specialized predators. Mammals In North America, Rodents , large Mastodont s and Gomphothere s, and opossums continued successfully, while hoofed animals ( Ungulate s) declined, with Camel , Deer and Horse all seeing populations recede. Rhinos , Tapirs and Chalicothere s went extinct. Carnivores including the Weasel family diversifed, and Dog s and fast-running hunting Bear s did well. Ground Sloth s, huge Glyptodont s and Armadillo s came north with the formation of the Isthmus Of Panama . In Eurasia Rodents did well, while Primate distribution declined. Elephant s, Gomphothere s and Stegodon ts were successful in Asia, and Hyraxes migrated north from Africa. Horse diversity declined, while Tapir s and rhinos did fairly well. Cow s and Antelope s were successful, and some Camel species crossed into Asia from North America. Hyaenas and early Saber-toothed Cat s appeared, joining other predators including dogs, bears and weasels. Africa was dominated by hoofed animals, and Primate s continued their evolution, with Australopithecine s (some of the first Hominid s) appearing in the late Pliocene. Rodent s were successful, and elephant populations increased. Cows and antelopes continued diversification and overtaking Pig s in numbers of species. Early Giraffe s appeared, and camels migrated via Asia from North America. Horses and modern rhinos came onto the scene. Bears, dogs and weasels (originally from North America) joined cats, hyaenas and Civet s as the African predators, forcing hyaenas 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. Litoptern s and the Notoungulate s, South American natives, did well. Small weasel-like carnivorous Mustelid s and Coati s migrated from the north. Grazing Glyptodont s, browsing giant Ground Sloth s and smaller Armadillo s did well. The Marsupial s remained the dominant Australia n mammals, with herbivore forms including Wombat s and Kangaroo s, and the huge Diprotodont s. Carnivorous marsupials continued hunting in the Pliocene, including Dasyurid s, the dog-like Thylacine and cat-like '' Thylacoleo ''. The first rodents arrived, while Bat s did well, as did ocean-going Whale s. The modern duck-billed Platypus , a Monotreme , appeared. Birds (Text required) PLIOCENE OCEANS Oceans continued to be relatively warm during the Pliocene, though 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 Cow s, Seal s and Sea Lion s. SUPERNOVAE In 2002, astronomers discovered 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 150 light-years of Earth and that one or more Supernovae may have occurred in this group at that time. Such a close explosion could have damaged the Earth's ozone layer and caused the extinction of some ocean life (consider that at its peak, a supernova of this size could produce that same amount of Absolute Magnitude as an entire galaxy of 200 billion stars). ''(Comins, Kaufmann pp. 359)'' REFERENCES
EXTERNAL LINKS
|
|
|