Pliocene Epoch free essay sample

During this time the world became much more like it is today, with ice caps, modern mammals, relatively modern geography, and the evolution of prehistoric man (ape man) ( see figure 1). â€Å"The Pliocene was a time of global cooling after the warmer Miocene. The cooling and drying of the global environment may have contributed to the enormous spread of grasslands and savannas during this time. The change in vegetation undoubtedly was a major factor in the rise of long-legged grazers who came to live in these areas. Additionally, the Panamanian land-bridge between North and South America appeared during the Pliocene, allowing migrations of plants and animals into new habitats. Of even greater impact was the accumulation of ice at the poles, which would lead to the extinction of most species living there, as well as the advance of glaciers and ice ages of the Late Pliocene and the following Pleistocene. † (Palmer 1999) The world was approaching that of today, and continents had taken up their present-day positions. We will write a custom essay sample on Pliocene Epoch or any similar topic specifically for you Do Not WasteYour Time HIRE WRITER Only 13.90 / page During this time, India collided with Asia and gave rise to the Himalayan Mountains, the Himalayan uplift triggering a great global cooling (or accelerating the already unfolding cooling process) The Pliocene saw the continuation of the climatic cooling that had began in the Miocene, with subtropical regions retreating equatorially, the beginning of the large ice caps, especially in Antarctica, and the northern hemisphere lands and ocean cooling likewise. Antarctica was not yet completely frozen. In the northern hemisphere there is a gradual southward migration of marine invertebrates. Reflecting the cooling trend, Arctic species appear in Britain, and later, in the Mediterranean. So much so that the horizon of a normal marine bed can be determined by the percentage of species that (a) are extinct, (b) survive in more northern latitudes, and (c) are today found in more southern latitudes. ( Todd 2002) The Pliocene saw an almost complete turnover of molluscan species in numerous locations. (See figure 2) This is not to say that extinction rates approached 100% on the species level. In many cases, species ranges simply flowed back and forth with shifting climate. This is particularly noticeable in regions with long north-south coastlines, as in North America. Some of the Zanclean Pacific coast species simply relocated to the Gulf of California in the Gelasian, since the Gulf remained semitropical throughout the Pliocene. Pliocene vegetation was very like todays. Grasslands replaced forests, so grazing mammals spread at the expense of browsers. Cattle, sheep, antelopes, gazelles, and other bovids reached their peak. North American mammals included horses, camels, deer, pronghoms, peccaries, mastodons, beavers, weasels, dogs, and saber-toothed cats. Rhinoceroses and protoceratids died out in North America. The one-toed horse appears for the first time. The Pliocene period is regarded by many zoologists as the climax of the Age of Mammals. This epoch is characterized by the appearance of all of the presently existing orders and families, and many of the existing genera of mammals. The Pliocene was a time of great migration, owing to the appearance of new land bridges. The North American three-toed Hipparion horse crossed the Bering Straits land bridge and entered Asia and Europe, while mastodons entered the Americas from Asia. During the late Pliocene, about 3 million years ago, the isthmus of Panama ended South Americas isolation. The armadillo, ground sloth, opossums, and phorusrhacid birds were among the animals that migrated north from South America. And dogs, cats, bears, horses, mastodons, and others animals invaded South America from the north. This was catastrophic for some of the local animals, especially the big marsupial carnivores. Even today more than half the genera of South American mammals are descended from northern species. Australia, still isolated, saw rodents rafting in on mats of vegetation drifting south from Indonesia. (Serrano 1999) Primate evolution during the Pliocene is characterized by two major developments. Monkeys, which were relatively few and geographically restricted in the Miocene, spread throughout the Old World. The other event is the evolution of bipedal apes, or the first hominines (early humans). As many as eight different species of bipedal apes evolved during the Pliocene, all from a common ancestor that lived in Africa at least 4. 5 million years ago. The emerging avanna grasslands and retreating forests caused some apes to come down from the trees and take up life in the open, where they co-existed with early elephants, antelopes, and other types of animals. An erect posture was necessary for these vulnerable creatures to watch for predators, which also freed the hands for the use of makeshift tools (sticks etc). Two anthropologists, Donald Johansson and Tim White discovered a nd named Australopithecus afarensis better known as â€Å"Lucy† in 1974. The location she was found in was Hadar, Ethiopia in the Afar region, in mid-November. She was named Australopithecus afarensis after the Afar region that she was found in. For millions of years Lucy’s bones were buried where she had died, and erosion brought them back to the surface where there were discovered. Around midday, Johansson discovered several fossilized bones. After several hours of excavating and uncovering these bones, Johansson’s team had discovered about 40% of a small, bipedal, female skeleton. The specimen was 3. 5 million years old and is the oldest, most complete, and best-preserved skeleton ever found of Australopithecus. Later on in the night to celebrate, the team played some tunes, and after listening to the popular Beatles Song, Lucy in the Sky with Diamonds, named the specimen Lucy. From Lucy’s skeleton we can infer many physical traits she possessed. Lucy’s thighbone suggests that she was three feet, seven inches in height. She had long arms and short legs as well as an ape like chest. Lucy also had a V shaped jaw. Her pelvis and lower limbs show all the adaptation necessary for an upright stance. The state of her bone growth and the presence of her wisdom teeth suggest that she died in her mid-twenties. See figure 3) Supernovas near Earth are rare today, but during the Pliocene era of Australopithecus supernovas happened more often. Their source was an interstellar cloud called Sco-Cen that was slowly gliding by the solar system. ( See figure 4) Within it, dense knots coalesced to form short-lived massive stars, which exploded like popcorn. Researchers estimate (with considerable uncertainty) that a supernova less than 25 light years away would extinguish much of the life on Earth. The blast neednt incinerate our planet. All it would take is enough cosmic rays to damage the ozone layer and let through lethal doses of ultraviolet (UV) radiation. Our ancestors survived the Pliocene blasts only because the supernovas werent quite so close. We know because we can still see the cloud today. It is 450 light years from Earth and receding in the direction of the constellations Scorpius and Centaurus (hence the clouds name, Sco-Cen). Astronomer Jesus Maiz-Apellaniz of Johns Hopkins University recently backtracked Sco-Cens motion and measured its closest approach: 130 light years away about 5 million years ago.