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英语长篇文章阅读1寒武纪大爆发 动物王国出现
Science and technology
The Cambrian explosion
Kingdom come
Chinese palaeontologists hope to explain the rise of the animals
AMONG the mysteries of evolution, one of the most profound is what exactly happened at the beginning of the Cambrian period.
Before that period, which started 541m years ago and ran on for 56m years, life was a modest thing.
Bacteria had been around for about 3 billion years, but for most of this time they had had the Earth to themselves.
Seaweeds, jellyfish-like creatures, sponges and the odd worm do start to put in an appearance a few million years before the Cambrian begins.
But red in tooth and claw the Precambrian was not—for neither teeth nor claws existed.
Then, in the 20m-year blink of a geological eye, animals arrived in force.
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.
The sudden evolution of this megafauna is known as the Cambrian explosion.
But two centuries after it was noticed, in the mountains of Wales after which the Cambrian period is named, nobody knows what detonated it.
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”.
The “Snowball Earth” refers to a series of ice ages that happened between 725m and 541m years ago.
These were, at their maxima, among the most extensive glaciations in the Earth’s history.
They alternated, though, with periods that make the modern tropics seem chilly: the planet’s average temperature was sometimes as high as 50C.
Add the fact that a supercontinent was breaking up at this time, and you have a picture of a world in chaos.
Just the sort of thing that might drive evolution.
Dr Zhu and his colleagues hope to find out exactly how these environmental changes correspond to changes in the fossil record.
The animals’ carnival
Fortunately, China’s fossil record for this period is rich.
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.
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.
Portents of the modern world
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.
What these embryos would have grown into is unclear. But some might be the ancestors of the Cambrian megafauna.
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.
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.
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.
Each of Dr Chu’s oxidation events corresponds with an increase in the size, complexity and diversity of life, both plant and animal.
What triggered what, however, is unclear.
There may have been an increase in photosynthesis because there were more algae around.
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.
The last—and most dramatic—rise in oxygen took place towards the end of the Ediacaran.
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.
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.
Dr Zhu suspects this global environmental shift propelled the evolution of complex animals.
Dr Zhu also plans to push back before the Ediacaran period.
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.
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.
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.
Dr Chen, indeed, first made his name in 1984, when he excavated one at Chengjiang in Yunnan province.
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.
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.
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.
Dr Zhu hopes to map changes in the distribution of these chemicals across time and space.
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.
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.
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.
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.
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.
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.
英语长篇文章阅读2巴西水资源 无水可喝
Water in Brazil
Nor any drop to drink
Dry weather and a growing population spell rationing
BRAZIL has the world's biggest reserves of fresh water. That most of it sits in the sparsely populated Amazon has not historically stopped Brazilians in the drier, more populous south taking it for granted. No longer. Landlords in S?o Paulo, who are wont to hose down pavements with gallons of potable water, have taken to using brooms instead. Notices in lifts and on the metro implore paulistanos to take shorter showers and re-use coffee mugs.
S?o Paulo state, home to one-fifth of Brazil's population and one-third of its economic activity, is suffering the worst drought since records began in 1930. Pitiful rainfall and high rates of evaporation in scorching heat have caused the volume of water stored in the Cantareira system of reservoirs, which supplies 10m people, to dip below 12% of capacity. This time last year, at the end of what is nominally the wet season, it stood at 64%.
On April 21st the governor, Geraldo Alckmin, warned that from May consumers will be fined for increasing their water use. Those who cut consumption are already rewarded with discounts on their bills. The city will tap three basins supplying other parts of the state, but since these reservoirs have also been hit by drought and supply hydropower plants, fears of blackouts are rising.
Without a downpour, Sabesp, the state water utility, expects Cantareira's levels to sink beneath the pipes which link reservoirs to consumers a week after S?o Paulo hosts the opening game of the football World Cup on June 12th. To tide the city over until rains resume in November, it is installing kit to pump half of the 400 billion litres of reserves beneath the pipes, at a cost of 80m reais. The company says this “dead volume”, never before used, is perfectly treatable. Some experts have expressed concerns about its quality.
Mr Alckmin has not ruled out tightening the spigots. Flow from taps in parts of S?o Paulo has already become a trickle, for which Sabesp blames maintenance work. Widespread cuts could hurt the governor's re-election bid in October. Hours after he announced the latest measures, a thirsty mob set fire to a bus.
Paulistanos use more water than most Brazilians, but lose less of it to leaks: 35%, compared with a national average of 39%. Sabesp, listed on the New York Stock Exchange but majority-owned by the state government, is a paragon of good governance, says John Briscoe, a water expert at Harvard and a former head of the World Bank mission in Brazil.
The problem exposed by the drought is that supply has not kept pace with the rising urban population. Facing a jumble of overlapping municipal, state and federal regulations, investment in storage, distribution and treatment has lagged behind. And not just in S?o Paulo; the national water regulator has warned that 16 projects in the ten biggest cities must be completed by 2015 to prevent chronic water shortages over the next decade. So far only five are finished; work on some has not begun. Short-term measures should keep the water trickling for now. But the well of temporary solutions will eventually run dry.
英语长篇文章阅读3德国公司的管理 董事会的多元化
Business
Corporate governance in Germany
Diversifying the board
German boards have long been cosy men's clubs. But things are changing
HERMANN JOSEF ABS liked to joke, What's the difference between a doghouse and the supervisory board?
The doghouse is for the dog; the supervisory board is for the cat.
For those unfamiliar with the nuances of German humour, for the cat is slang for something like trash.
The late banker would know: while running Deutsche Bank from 1957 to 1967, he also sat on dozens of supervisory boards.
This was the peak of Deutschland AG, a clique of long-serving bosses, autocratic chairmen, do-nothing board members and their financier friends.
Big German companies' supervisory boards are supposed to act as a check on their management boards.
But in practice their relations were too cosy for this.
This past year the stumbles of two titans seemed to highlight how much corporate power is still concentrated in few hands in the Germanspeaking world.
As 2013 began Gerhard Cromme was chairman of the supervisory boards of both Siemens, an industrial conglomerate, and ThyssenKrupp, a steelmaker.
But big losses at foreign mills and heavy fines over a cartel case cost him the chairmanship at ThyssenKrupp.
Then in July, a boardroom bunfight at Siemens ended with the departure of Peter Lscher, the chief executive.
Mr Cromme belatedly called for his firing—but only after hiring him and protecting him for years.
Josef Ackermann, a Swiss former boss of Deutsche Bank and a Siemens board member, had defended Mr Lscher.
When Mr Lscher went, so did he.
Shortly before this he had quit as chairman of Zurich, a Swiss insurer, whose chief financial officer had committed suicide, leaving a note berating Mr Ackermann.
Now he has no big corporate job, there have been reports that Mr Ackermann may have to step down as a trustee of the World Economic Forum after its gabfest in Davos this week.
At first glance, corporate power in Germany still looks male, German and concentrated.
But its boardrooms are slowly getting more diverse.
In 2003 the average supervisory-board member at a public company sat on 1.9 boards; now the figure is 1.6.
A 2001 cut in tax on sales of shares let banks and insurance companies, which played big roles as lenders and part-owners, start disentangling themselves from companies.
Into the gaps, and onto the boards, has come a new generation of more active members.
Boards have little choice but to be sharper, says Christoph Schalast of Frankfurt School of Finance and Management.
Many companies are now paying fines and settlements for their behaviour before the financial crisis.
A 2010 change in the law doubled the statute of limitations for such misdeeds to ten years.
Progress on making boards more international is slower.
Eight of the largest 30 public companies have foreign bosses, but the rest of their boards' members are predominantly German, even at the country's most multinational firms.
But Burkhard Schwenker, the boss of Roland Berger, a consulting firm, says that counting passports is simplistic: what matters more is international experience, which German firms increasingly look for when recruiting both management-and supervisory-board members.
If boards are becoming more professional and diverse, is accumulation of board seats a bad thing in itself?
Jrg Rocholl, the president of the European School for Management and Technology, says that studies disagree on whether busy board members are better or worse for profits.
But he agrees that boards are becoming more capable, and says this has been a factor in Germany's economic revival.
Pay for German board members is going up; but these days, members are earning it.
