经济学人下载:寒武纪大爆发 动物王国出现

Science and technology
科学技术

The Cambrian explosion
寒武纪大爆发

Kingdom come
动物王国出现

Chinese palaeontologists hope to explain the rise of 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 at the 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 a modest 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 the Earth 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 the Cambrian 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 not—for 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 kingdom—arthropods, brachiopods, coelenterates, echinoderms, molluscs and even chordates, the branch from which vertebrates went on to develop—are 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 Cambrian period 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 and Palaeontology, plan to change that with a project called “From the Snowball Earth to the Cambrian 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 541m years 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 Earth’s 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 planet’s average 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 a world 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 changes correspond 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, China’s 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 the Ediacaran fauna—a handful of strange creatures found in Australia, Canada and the English Midlands that lived in the Ediacaran period, between 635m and 541m years ago, and which bear 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 led by Xiao Shuhai of the Virginia Polytechnic Institute, in America, discovered a 580m-year-old Lagersttte—a place where fossils are particularly well preserved—in a geological formation called 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 microscopic sponges, small tubular organisms of unknown nature, things that look like jellyfish but might not 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 of the 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 Xuelei of the Institute of Geology and Geophysics in Beijing and his colleagues have been looking at carbon 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 12C—a light isotope of carbon that is more easily incorporated by living organisms into organic matter than its heavy cousin, 13C—increased on 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 went up, because more oxygen would mean more oxidisation of buried organic matter. That would 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 Chu’s oxidation events corresponds with an increase in the size, complexity and diversity 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 algae around.
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 that would 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 last—and most dramatic—rise 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 this surge started just after the final Precambrian glacial period about 560m years ago, and went 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。

These dates overlap with those of signs of oxidation found in rocks in other parts of the world, confirming that whatever was going on affected the entire planet.
这些数据和全球其他地方发现的化石中的氧化物一起确定了到底是什么将影响整个星球。

Dr Zhu suspects this global environmental shift propelled the evolution of complex animals.
朱博士认为是全球环境的变化促进了复杂动物的进化。

Dr Zhu also plans to push back before the Ediacaran period.
朱博士还计划回推到埃迪卡拉纪之前。

Other researchers have found fossils of algae and wormlike creatures in rocks in northern China that pre-date the end of the Marinoan glaciation, 635m years ago, which marks the boundary between the Ediacaran and the Cryogenian period that precedes it.
其他研究者已经在中国北部的石块中发现了藻类和类似虫子的生物的化石，其年代在6.35亿年之前的圣马力诺冰期末端之前，圣马力诺冰期确定了其之前埃迪卡拉纪和成冰纪之间的边界。

Such fossils are hard to study, so Dr Zhu will use new imaging technologies that can look at them without having to clean away the surrounding rock, and are also able to detect traces of fossil organic matter invisible to the eye.
这些化石很难去研究，所以朱博士利用可以清晰成像而不用去清除周边石块的新成像技术，并且可以探测不被肉眼可见的化石有机物的踪迹。

Besides digging back before the Ediacaran, the new project’s researchers also intend to analyse the unfolding of the Cambrian explosion itself by taking advantage of other Lagersttten—for China has several that date from the Cambrian.
除了研究埃迪卡拉纪之前以外，新项目的研究者还利用其他生物群去分析未解开的寒武纪大爆炸，因为中国有好几个这样寒武纪的群落。

Dr Chen, indeed, first made his name in 1984, when he excavated one at Chengjiang in Yunnan province.
陈博士因为1984年发掘了云南澄江生物群而出名，

It dates from 525m years ago, which make it 20m years older than the most famous CambrianLagersttte in the West, the Burgess shale of British Columbia, in Canada.
澄江生物群大概在5.25亿年以前，这就使得他比西方著名的加拿大不列颠哥伦比亚的波基斯页岩寒武纪群落早了2000万年。

The project’s researchers plan to see how, evolutionarily speaking, the various Lagerst?tten relate to one another, to try to determine exactly when different groups of organisms emerged.
这个项目的研究者计划从进化学上解释，不同的群落是怎么和其他的群落发生联系，并且试图解决到底什么时候出现了不同的生物分类。

They will also look at the chemistry of elements other than carbon and oxygen—particularly nitrogen and phosphorous, which are essential to life, and sulphur, which often indicates the absence of oxygen and is thus antithetical to much animal life.
他们不单单只是观察氧和碳元素，尤其是生命必须的氮和磷，以及经常指示缺少氧且和大部分动物生命对立的硫。

Dr Zhu hopes to map changes in the distribution of these chemicals across time and space.
朱博士希望绘制这些元素随着时间和空间分布变化图，确认这些变化的关联性，

He will assess how these changes correlate, whether they are related to weathering, mountain building and the ebb and flow of glaciers, how they could have affected the evolution of life, and how plants and animals might themselves have altered the chemistry of air and sea.
它们是否和天气，造山，冰川的起伏有关，他们怎样影响生命的进化，以及动植物他们自己是如何改变空气和海洋中的化学组成。

Most ambitiously, Dr Zhu, Dr Xiao and their colleagues hope to drill right through several fossiliferous sites in southern China where Ediacaran rocks turn seamlessly into Cambrian ones.
朱博士，肖博士以及他们的团队很有雄心的希望在中国南部那些无缝连接埃迪卡拉纪和寒武纪的几个含有化石的地方穿凿而过。

Such places are valuable because in most parts of the world there is a gap, known as an unconformity, between the Ediacaran and the Cambrian.
这些地方都很有价值，世界的大部分地区，埃迪卡拉和寒武纪之间都有空白，这种空白被称为不整合面。

Unconformities are places where rocks have been eroded before new ones are deposited, and the widespread Ediacaran-Cambrian unconformity has been a big obstacle to understanding the Cambrian explosion.
不整合面地方的石块在新的沉积之前已经被侵蚀，埃迪卡拉纪-寒武纪之间广泛的不整合面是了解寒武纪大爆发的一个重大障碍。

With luck, then, a mystery first noticed in the Welsh mountains in the early 19th century will be solved in the Chinese ones in the early 21st.
幸运的是，在19世纪早期威尔士群山中发现的神奇事件将被21世纪中国发现的群落所解决。

If it is, the origin of the animal kingdom will have become clear, and an important gap in the history of humanity itself will have been filled.
如果是的话，那动物王国的起源将会变得更清晰，人类历史中一个重要的空白将被填补。