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Permian, a Catastrophic Times--论文代写范文精选

2015-10-03 来源: 51due教员组 类别: Essay范文

51due论文代写网精选代写范文:“Permian, a Catastrophic Times”这篇essay讲的是二叠纪是一个拥有着约2.5亿年前多生物的黄金时代,但遭受了灾难性的事件,地球上大约95%的生物被消灭。与恐龙的灭绝相比,这一次可能是世界上最大规模的生物灭绝。一些地质学家和科学家努力寻找导致这个灾难性灭绝的原因。尽管研究人员知道了一些事件的细节,但很多方法和实践也没有真正找出寻出原因所在。

The Permian, a golden age with biodiversity 250 million years ago, suffered a catastrophic event that approximately wiped out 95% of species on the planet. Compared with the demise of dinosaurs, this one happened earlier could be the biggest mass extinction in the world. To explore the actual reasons leading to this particularly disastrous extinction, several geologists and scientists contributed their efforts to it. Although researchers knew few details about that event, many methodologies and practices were applied to this situation in order to prove that whether their theories are practical or not.
In the first place, attentions were paid to a sub-Arctic wilderness, a region of Siberian known as the Traps, in the early 1990s. Dated back to 250 million years ago, this place was a blazing torrent of lava, the flood of lava lasted for millions of years. Vincent Courtillon had his theory that there was a possibility that the disruption of cooling followed by massive lava eruption which potentially had the ability to cause a temperature rise of 5 degrees could result in such a large-scale mass extinction like this. Whereas the geologist Peter Ward in the US disagrees with that theory, he claimed that an increase of 10 degrees in temperature could probably trigger a mass extinction like this scale through analyzing the data collected in the Siberian Traps, but a mere rise of 5 degrees could hardly wipe out 95% of all life forms, which means that the “flood basalt eruption” was not extremely deadly. Therefore, Vincent’s previous theory seems not to be that convincing.
Until 1998, Michael Rampine in the US decided to evaluate the timescale of the Permian mass extinction to speculate if it was an “instantaneous killer” or something slower. He went to the Alps, which is one of the only places where there are Permian fossils. By analyzing rock sedimentation rates in Alps, the conclusion that the Permian mass extinction merely stalked the earth for less than 10000 years was made. From a geological perspective, this could be allocated into “instantaneous killer”. One thing occurred to him that a meteorite could possibly cause this. Just like the end of dinosaurs, one 50% bigger meteorite would be capable of triggering such a severe environmental change overnight. However, the lack of evidence could not prove that there was a meteorite strike because they could not find crater, the trace of meteorite. Fortunately, the London scientist, Adrian Jones, used his experiment to demonstrate that if the meteorite was massive enough, it not only caused a wider, shallower crater, but also melted the Earth’s crust. Eventually, the lava would be released. As a result, lava would fill the crater and flow beyond the edges of the crater as well as the original crater structure. However, this seemed to be too simple to be believed.
Later, one researcher, Greg Rettaleck headed into the Antarctic to do research on Permian rock beds. According to the internal structure of some quartz grains, they might be formed by a very energetic process. However, a meteorite, this choice was ruled out in the situation where there was no sign of fragments of minerals and, most importantly, iridium - characteristic of space materials.
Finally, the British geologist, Paul Wignall, found the best samples of Permian rock beds in Greenland. Based on the analysis of these valuable samples, another different version of the Permian mass extinction was revealed. There were three distinctive phases during that period of time. Firstly, some life forms on the land disappeared over 4000 years, then as the temperature of the ocean rose, in just 5000 years, sea creatures gave up struggling , and for another 3500 years, the misfortune went back to the land to kill most typical creatures. During his process of analyzing, one problem hindered him, because he found a dramatic increase in carbon-12 over time but no reason had been found. Thanks to geologist Gerry Dickens, who understands how to generate large amount of carbon-12 within a short time, through frozen methane hydrate, which exactly addressed this puzzle. In addition, the theory promoted by Gerry Dickens motivated Paul Wignall to link the Siberian Traps with first phase.
Above all, there were two “Permian Killer” at different time period. The flood of lava caused an increase of 5 degrees, which killed many sea creatures and species on land. Then intensive frozen methane hydrate began to produce methane, which led to another temperature rise of 5 degrees. At that time, 95% of species could not tolerate it. .-M
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