2015考研英语阅读寒武纪大爆发

　　The Cambrian explosion

　　寒武纪大爆发

　　Kingdom come

　　动物王国出现

　　Chinese palaeontologists hope to explain the riseof the animals

　　中国古生物学家希望解释动物的起源

　　AMONG the mysteries of evolution, one of the most profound is what exactly happened atthe beginning of the Cambrian period.

　　在众多进化之谜中，其中意义最深远的就是在寒武纪开始时期到底发生了什么。

　　Before that period, which started 541m years ago and ran on for 56m years, life was amodest thing.

　　在寒武纪之前，从5.41亿年前开始持续5600万年的时代里，生命是适度存在的。

　　Bacteria had been around for about 3 billion years, but for most of this time they had had theEarth to themselves.

　　细菌已经存在了大约30亿年，但是在多数时间里，它们主宰着地球。

　　Seaweeds, jellyfish-like creatures,sponges and the odd worm do start to put in an appearance a few million years before theCambrian begins.

　　海藻、类似水母的生物、海绵生物和奇怪的虫子确实在寒武纪开始的前几百万年已经出现。

　　But red in tooth and claw the Precambrian was notfor neither teeth nor claws existed.

　　但是前寒武纪时期却不是腥牙血爪，因为那个时候牙齿和爪子都没有出现。

　　Then, in the 20m-year blink of a geological eye, animals arrived in force.

　　然后，在地质学看来一眨眼的2000万年中，动物大规模的出现了。

　　Most of the main groups of the animal kingdomarthropods, brachiopods, coelenterates,echinoderms, molluscs and even chordates, the branch from which vertebrates went on todevelopare found in the fossil beds of the Cambrian.

　　人们在寒武纪群落里发现了动物王国的主要动物集群，包括腕足、腔肠、棘皮、软体和脊索。

　　The sudden evolution of this megafauna is known as the Cambrian explosion.

　　寒武纪因威尔士的群山而得名，

　　But two centuries after it was noticed, in the mountains of Wales after which the Cambrianperiod is named, nobody knows what detonated it.

　　在寒武纪被注意到的两个多世纪里，没人知道到底为什么会发生大爆炸。

　　A group of Chinese scientists, led by Zhu Maoyan of the Nanjing Institute of Geology andPalaeontology, plan to change that with a project called From the Snowball Earth to theCambrian explosion: the evolution of life and environment 600m years ago.

　　由南京地质古生物研究所的朱茂炎领导的中国科学家小组计划通过一个名为从雪球事件到寒武纪大爆发：距今6亿年前后的生物与环境演变的项目改变这种情况。

　　The Snowball Earth refers to a series of ice ages that happened between 725m and 541myears ago.

　　雪球事件指的是7.25亿-5.41年前一系列的冰川时代。

　　These were, at their maxima, among the most extensive glaciations in the Earths history.

　　在顶峰时期，它们是地球史上最大规模的冰川时期。

　　They alternated, though, with periods that make the modern tropics seem chilly: the planetsaverage temperature was sometimes as high as 50C.

　　不过他们是交替发生的，在某些时候，使得现在的热带地区变的寒冷，有时候全球的平均温度却高达50度。

　　Add the fact that a supercontinent was breaking up at this time, and you have a picture of aworld in chaos.

　　从而导致了一个超大陆分裂，从此我们就有了一个混乱的地球，

　　Just the sort of thing that might drive evolution.

　　就是这些事情可能导致进化的发生。

　　Dr Zhu and his colleagues hope to find out exactly how these environmental changescorrespond to changes in the fossil record.

　　朱博士和他的同事希望从化石记录的变化中发现这个时期环境是如何确切变化的。

　　The animals carnival

　　动物狂欢节

　　Fortunately, Chinas fossil record for this period is rich.

　　幸运的是，中国在这个时期的化石资料是非常丰富的。

　　Until recently, the only known fossils of Precambrian animals were what is called theEdiacaran faunaa handful of strange creatures found in Australia, Canada and the EnglishMidlands that lived in the Ediacaran period, between 635m and 541m years ago, and whichbear little resemblance to what came afterwards.

　　直到目前，唯一知道的前寒武纪一少部分化石是埃迪卡拉动物群。它们生活与生活在距今6.35亿年到5.42亿年之间埃迪卡拉纪，在澳大利亚、加拿大、英格兰中部等地区被发现，但是他们和寒武纪的生物相似性很少。

　　In 1998, however, a team led by Chen Junyuan, also of the Nanjing Institute, and another ledby Xiao Shuhai of the Virginia Polytechnic Institute, in America, discovered a 580m-year-oldLagerstttea place where fossils are particularly well preservedin a geological formationcalled the Doushantuo, which spreads out across southern China.

　　然而，1998年，一个由同样来自南京所的陈俊元和美国弗吉尼亚理工大学的肖书海共同领导的小组在中国南部一个广泛存在的陡山沱地质构造中发现了一个距今5.8亿年且保存出奇的好的生物群。

　　Portents of the modern world

　　现代世界的前兆

　　This Lagersttte has yielded many previously unknown species, including microscopicsponges, small tubular organisms of unknown nature, things that look like jellyfish but mightnot be and a range of what appear to be embryos that show bilateral symmetry.

　　这个生物群落发现了许多之前不知道的物种，包括微型海绵生物，不知名物种的小管器官，一些似是而非的软体动物，以及一些有对称结构的像是胚胎的生物。

　　What these embryos would have grown into is unclear. But some might be the ancestors ofthe Cambrian megafauna.

　　这些胚胎将会长成什么不得而知，但是他们中的一些可能就是寒武纪大型动物的祖先。

　　To try to link the evolution of these species with changes in the environment, Chu Xueleiof the Institute of Geology and Geophysics in Beijing and his colleagues have been looking atcarbon isotopes in the Doushantuo rocks.

　　为了把这些物种的进化和环境变化联系起来，北京地质与地球物理研究所的储雪雷和他的同事用碳同位素方法测试陡山沱石块。

　　They have found that the proportion of 12Ca light isotope of carbon that is more easilyincorporated by living organisms into organic matter than its heavy cousin, 13Cincreasedon at least three occasions during the Ediacaran period.

　　他们发现在埃迪卡拉纪有至少三次12C的增加，而较轻的碳同位素12C相比于它的同胞13C更容易被生物体吸收转化为有机物。

　　They suggest these increases mark moments when the amount of oxygen in seawater wentup, because more oxygen would mean more oxidisation of buried organic matter. Thatwould liberate its 12C, for incorporation into rocks.

　　他们推测这些增长标志当时海水中的氧含量在增长，因为更多的氧气意味着更多的埋藏的有机物的氧化。他们在变成化石的过程中就将释放12C。

　　Each of Dr Chus oxidation events corresponds with an increase in the size, complexity anddiversity of life, both plant and animal.

　　褚博士的每个氧化事项都与动植物在其体积，复杂性、多样性上的增加有关。

　　What triggered what, however, is unclear.

　　然而，哪一个引发哪一个却不得而知。

　　There may have been an increase in photosynthesis because there were more algaearound.

　　这有可能因为出现了更多的藻类，光合作用增强，

　　Or eroded material from newly formed mountains may have buried organic matter thatwould otherwise have reacted with oxygen, leading to a build-up of the gas.

　　或者是新形成的山脉上的腐蚀物质埋藏本该和氧气反应的有机物，导致气体的增加。

　　The lastand most dramaticrise in oxygen took place towards the end of the Ediacaran.

　　最戏剧性的，也是氧气含量最后的增长发生在埃迪卡拉纪末期。

　　Follow-up work by Dr Zhu, in nine other sections of the Doushantuo formation, suggests thissurge started just after the final Precambrian glacial period about 560m years ago, andwent on for 9m years.

　　后续的工作由朱博士完成，有九个其他的陡山沱构造说明这个激增仅仅是在最后一次前寒武纪冰川之后，大约5.6亿年前，并且持续了900万年。