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Then in the early 1950s Emiliani produced the first complete record of the waxings and wanings of past glaciations. It came from a seemingly odd place. The seafloor single-cell marine organisms called "foraminifera" house themselves in shells made from calcium carbonate. When the foraminifera die, sink to the bottom, and become part of seafloor sediments, the carbonate of their shells preserves certain characteristics of the seawater they inhabited. In particular, the ratio of a heavy isotope of oxygen (oxygen-18) to ordinary oxygen (oxygen-16) in the carbonate preserves the ratio of the two oxygens in water molecules.
It is now understood that the ratio of oxygen isotopes in seawater closely reflects the proportion of the world's water locked up in glaciers and ice sheets. A kind of meteorological distillation accounts for the link. Water molecules containing the heavier isotope tend to condense and fall as precipitation slightly sooner than molecules containing the lighter isotope. Hence, as water vapor evaporated from warm oceans moves away from its source, its oxygen-18 returns more quickly to the oceans than does its oxygen-16. What falls as snow on distant ice sheets and mountain glaciers is relatively depleted of oxygen-18. As the oxygen-18-poor ice builds up the oceans become relatively enriched in the isotope. The larger the ice sheets grow, the higher the proportion of oxygen-I 8 becomes in seawater—and hence in the sediments.
Analyzing cores drilled from seafloor sediments, Emiliani found that the isotopic ratio rose and fell in rough accord with the Earth's astronomical cycles. Since that pioneering observation, oxygen-isotope measurements have been made on hundreds of cores. A chronology for the combined record enables scientists to show that the record contains the very same periodicities as the orbital processes. Over the past 800,000 years, the global ice volume has peaked every 100,000 years, matching the period of the orbital eccentricity variation. In addition, "wrinkles" superposed on each cycle-small-decrease or surge in ice volume have come at intervals of roughly 23,000 and 41, 000 years, in keeping with the precession and tilt frequencies of the Earth's spin axis.
Which of the following best expresses the main idea of the passage？
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It is hard to love ants. Spiders and scorpions excepted, they are probably our least favorite insect. They give no honey; they do not brighten the air or chirp in hedgerows. Ants are small and dark and silent and live underground where they cannot be seen. They arc venomous and they bite. They teem and swarm, moving en masse, like robots, in cryptic legions. And they are ugly; their huge heads and tiny waists make their bodies seem like grotesque, anorexic versions of our own. The industry of ants is a constant reproach to us; their most surprising feature, their social organization, seems sinister and totalitarian. Only our luck in being several thousand times as big keeps us safe from them.
And ants, needless to say, do not love us. They hardly even notice us. This is hard to take. They challenge our anthropocentrism. For them, it seems we are not very important. And that is the truth of the matter. Ants arc the most successful organisms in evolutionary history: there are over 8,000 species, distributed everywhere on Earth except the polar regions. In Peru, 43 different kinds of ant have been recorded in a single tree. Compared with this, primates are just a flash in the pan. Ants antedate us and will undoubtedly outlast us. There are a million times more of them:10 million billion, it has been estimated, alive at any one time—a quarter of a million for every acre of land on the Earth's surface.
The greatest number of ant species, and the most spectacular, are to be found in tropical rainforests and savannahs. It is a common but disconcerting experience in such places to witness an invasion of driver ants, a predatory tribe that hunts at night as well as in the day. Driver ants move in columns a foot or so in width and a hundred yards in length, each composed of millions of individual ants. Waking up in the darkness with a marauding column in your tent, it seems as though a thick black oiled rope is running over your bed, over you, across the wall and out again: an endless skein of insects, running along each other's backs, antennae and mandibles threateningly erect. A column of driver ants will attack lizards, snakes, rodents, anything in its path. If you happen to be dead, the ants will eat you, too; if you are not, they will just bite you. With their preposterously over-developed jaws, individuals of the soldier castes that form. the flank of the column can scissor human flesh with ease. These are the rottweilers of the myrmecological world.
Ants can eat us, but we cannot eat them with any pleasure. Unlike termites (which have a rich oily taste something like pork scratchings), ants, with a tough outer layer of chitin and a nasty whiff of formic acid in their body tissues, are generally indigestible, except by other ants. Even anteaters prefer termites. Ants, furthermore, are resistant to hard radiation and, in the case of some species, industrial pollution; some can live in deserts; some can float; some can slow their metabolism down and survive under water for days on end.
The author feels that the fact that ants are always working ______.
Which of the following statements is supported by the passage？
Which of the following did the scientists do who first constructed a coherent, continuous
听力原文： More than 100,000 miners, railway workers and London bus drivers staged a one-day strike yesterday, creating chaos for British travelers on the worst day of industrial unrest for years.
The first strike in the railway industry for four years, in protest of proposed job cuts, is expected to halt the whole network on the busiest day of the week for train travel. The bus strike will worsen Londoners' misery. Bus drivers are protesting against new job practices and pay cuts as the bus system prepares for privatization.
Police forecast chaos on the roads ms commuters attempt to get to work by car. Hundreds of thousands of people are expected to stay at home to avoid the crush, likely to be made worse by bad weather. About 2 million people travel into London every day and most of them use public transport.
Miners' leaders hope 10,000 people will join a march through the Yorkshire coal town of Barnsley to protest at government-imposed pit closures which will cost 15,000 miners their jobs.
Prime Minister John Major called the railway workers' action "deplorable" on Thursday. But union leaders say they believe the public, concerned at the inexorable rise in unemployment after two years of recession, understand their action.
Yesterday's strike led to complete confusion for______.
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