Geological time period: Pliocene - Essay Example

Geological time period: Pliocene The Pliocene represents the geological time period between 5.4 - 2.4 million years ago. It is considered to be the youngest period in Cenozoic Era. The word “Pliocene” is Greek and means "current state prolongation". Speaking about other periods, the stages that identify their beginning and the end are easily determined but the accurate dates of the Pliocene epoch are not known. The time limits, which determine the beginning of the Pliocene were determined but scientists define them between the Miocene and Pliocene. The end of the period was defined as the beginning of the Pleistocene ice age. The period is very interesting for contemporary geology, therefore the given paper will discuss the Pliocene period with its major geological events, biological evolution, fossil groups, evolutionary breakthrough and paleoclimatic conditions. Paleogeography During the Pliocene period mainlands were still moving, changing their location. They were probably two hundred kilometers from their current positions and changed their location to become only seventy kilometers from their present site. As a result of this movement, in the Pliocene period South America was already very close to North America. This closeness opened the way for the Great American Interchange and eliminated distinguishing characteristics of South America’s fauna. At or near the close of the Pliocene, extensive upheavals took place in several different parts of the continent, especially on the Pacific slope. The rise of the Rocky Mountains continued, raising the western part of the Miocene beds 3000 feet higher than the eastern. The height of the Sierra was greatly increased by the rise of the mountains along the eastern fault-plane and the tilting of the whole block westward. The new valleys cut through the late basalt sheets of the Sierras are much deeper than the older valleys excavated in Cretaceous and Tertiary times, which is due to the greater height of the mountains and consequent greater fall of the streams (Scott, 1927). World climate was greatly influenced by the naturally formed Isthmus because Atlantic Ocean became separated from warm waters. One of the important changes during the Pliocene period was the formation of Mediterranean Sea as a consequence of clash of Africa with European Continent. Natural bridge was revealed between Asia and Alaska as a result of water level change. The change of water level also formed new shores (Figure 1). The volcanic activity in the Rocky Mountain and Pacific coast regions, which had begun in the Cretaceous, continued through the Pliocene. The great outflow of rhyolite which built up the Yellowstone Park plateau is referred to the Pliocene. Some of the enormous fissure eruptions, which flooded northern California and Nevada, southern Idaho, eastern Oregon, and Washington, with thick sheets of basalt, obliterating the valleys and revolutionizing the system of drainage, are probably Pliocene, as some are demonstrably Miocene (Scott, 1927). Figure 1 .Land areas in the Pliocene period. Source: pubs.usgs.gov Climate Generally, the climate of the Pliocene period was colder than the climate of Miocene geological time period. Shells and plants of the Pliocene testify about that. However, speaking about American Atlantic coast, it must be recognized that there the situation was the opposite: the water was colder during the Miocene and became warmer during the Pliocene. Moreover, recent investigations have also revealed the full connection of the sedimentary strata that were put in cycles during the Pliocene period. Such cycles are noticeable in rock layers and represent the proof of the temperature instability. For instance, paleoclimate investigations have demonstrated that the Pliocene generally considered to be the period of global cooling had a warm period (3.15-2.85 million years ago), characterized by comparatively constant hot weather. These data was found in the investigation of ocean fossils, which allowed to determine the temperature of water. Alterations in the waters flow, together with the warmth brought by the waters also testify about the warm period of the Pliocene. The middle period is considered to be the warm phase, while in the late Pliocene the weather was cool and meant the beginning of glaciation period. This period is characterized first of all by the formation of ice cap. The climate became colder, the weather was changing depending on the season and the climate was very close to modern. This period is characterized by global cooling due to ice sheets formation. More grasslands appeared instead of woods. Waters remained to be rather warm notwithstanding that they became colder. Due to the formation of the Arctic ice cap the weather became drier. Cold waters flow from the North. The climate of Pliocene is considered to be cooler than during the previous epoch. However, it is proved that the temperatures during the period of Pliocene were still much warmer than today (Figure 2). Figure 2. High temperatures during Pliocene. Source:  http://www.giss.nasa.gov/research/features/pliocene/  Flora and Fauna Colder and drier climate of Pliocene period greatly influenced plants and reduced the amount of tropical vegetation. On the contrary, the amount of deciduous and coniferous woods increased covering all the northern territory, while grasslands were met almost everywhere. Tropical plants were met only near the equator (Dockery, 1995). The fauna in Pliocene was very similar to modern with the difference that today we have some new interesting species. The period is characterized by the appearance of hominins and australopithecines. The movement of lands and their clash resulted in migration and appearance of’ mixed species of animals (Andel, 1994). Two main events in primate evolution happened in the Pliocene period are the following: the number of monkeys significantly increased; bipedal apes turned into the first hominins. Eight species was developing during this period with their common ancestor who lived 4.5 years ago. Today only one such species exists: Homo sapiens (Figure 3). Figure 3 . Human evolution Source: http://static.newworldencyclopedia.org/timeline/dfd846b5fceda40d3121c264ad08aa74.png The period is characterized by the appearance of new animals. Their appearance is connected with the forests’ turning into grasslands. There animals are short-neck giraffes, hippopotamuses, gazelles and antelopes (Wise, 1994). Fossils Flushed river sand and grave represented main outcropping layers of the given epoch. These fossils were somewhat unsolidificated (Figure 4). Figure 4. Fossils of Pliocene. Source: www.sandiego.gov/water/photos/fossils.jpg: David Dockery writes: These coarse-grained sediments commonly exhibit channels, cut and fill structures, scour surfaces, and large-scale cross-bedding. Minor beds of silt and clay are interbedded with the coarse-grained sediments. The general consensus is that the Citronelle Formation / Upland Complex was deposited as part of a gently sloping coastal plain was built up by the coalesced flood plains of numerous braided streams and rivers (Dockery, 1995). Gravel sediments were very old; they were buried for a long time and then moved by waters and finally placed as chert gravel. Pithecanthropus erectus is also prescribed to Pliocene period but further research is needed to prove this fact (Manning, 1989). The Pliocene period is characterized by great movement of molluscan species. Sometimes this movement was caused by the changes in climate that made species move to other place and then return back. This phenomena was noticed mostly in North America. With the shift of ice sheets some species were changed for more adaptive to cold climate (Chandler, 1997). Marine Shells in Pliocene period looks exactly like modern (see Figure 5). Figure 5. Shells. Source: http://chestofbooks.com/science/geology/Intro/Pliocene-Life.html Picture. 3, Marginella aurora, x 3/4, Miocene. 2, Nassa bidentata, x 3/4, Miocene and Pliocene. 3, Purpura conradi, x 2/3, Miocene. 4, Natica floridana, X 1/2, Miocene. 5, Mitra wilcoxi, x 1/2, Miocene. 6, Fasciolaria tulipa, x 1/2, Pliocene. 7, Typhis floridana, Pliocene. 8, Turbo rectogrammicus, x 1/2,Pliocene. (After Dall). Summary and conclusion During Pliocene mainlands were still moving, changing their location. The time limits, which determine the beginning of the Pliocene are not known but scientists define them between the Miocene and Pliocene. During the Pliocene period most of the continents moved to their current location (MacFadden, 1992). The weather became cooler and drier. Ice cap was formed, the world lost a lot of woods, which were replaced by grasslands. Flushed river sand and grave represented main outcropping layers of the given epoch (Comins, 2005). These fossils were somewhat unsolidificated. Two main events in primate evolution happened in the Pliocene period are the following: the number of monkeys significantly increased; bipedal apes turned into the first hominins (MacFadden, 1992). A lot of geological periods have been replicated in order to evaluate representation abilities and to learn more about the Earths climatic development. Replications of main ice age epochs usually offer perfect climate alteration scenarios (Robinson, 1997). If we want to know more about the period with warmer temperatures than today we should study the Pliocene. The climate during Pliocene is considered to be cooler than during the previous epoch. However, it is proved that the temperatures during the period of Pliocene was still much warmer than today Sources Dockery, III., David T. Rocks and Fossils Collected from Mississippi Gravel. Mississippi Geology, 1995: vol. 16, no. 2, pp. 25-42; Manning, E. M., and MacFadden, B. J. Pliocene three-toed horses from Louisiana, with comments on the Citronelle Formation. Tulane Studies in Geology, 1989: vol. 22, no. 2, pp. 35-46; MacFadden, B.J. Fossil horses: systematics, paleobiology, and evolution of the family Equidae. Cambridge University Press, Cambridge, 1992; Robinson, S.J. The geological column: a concept foundational to flood geology. Origins, 1997: (23):14-30; Wise, K.P. Australopithecus ramidus and the fossil record. Creation Ex Nihilo Technical Journal, 1994: 8:160-5; Comins, N. F. and W. J. Kaufmann.. Discovering the Universe, 7th edition. New York: Susan Finnemore Brennan, 2005; Andel, T. H. New Views on an Old Planet: A History of Global Change, 2nd edition. Cambridge: Cambridge University Press, 1994; Chandler, Mark A. The Climate of the Pliocene: Simulating Earths Last Great Warm Period (April 1997) available at http://www.giss.nasa.gov/research/features/pliocene/; Scott, William B. An Introduction To Geology, The Macmillan Company, 1927 Read More