英语听力：2013-09-18 地平线：黑洞吞噬—1

Nothing is more seductive than the unknown, nothing more compelling than a place of danger that lies beyond normal comprehension. Of all those places, perhaps the strangest of all are black holes. They are an exit point from the Universe, hidden trap

英语听力：2013-09-22 地平线：黑洞吞噬—2

High above your head, in the centre of our Milky Way Galaxy, a violent drama is about to unfold. Our super-massive black hole is getting ready to have dinner. As a gas cloud three times the size of the Earth, its caught in its gravitational hold. Acr

英语听力：2013-09-25 地平线：黑洞吞噬—3

Theres nothing anywhere near as extreme as a black hole. The disturbing truth about black holes is that there are boundary between the known universe and the place that would forever lie beyond the reach of science. They are in an anomaly of gravity

英语听力：2013-09-27 地平线：黑洞吞噬—4

But if watching matter tumble over the edge of a black hole might now be possible, it is only because of the efforts of a generation of astronomers to wrestle these dark dragons of the cosmos into the realms of scientific reality. As is often the cas

英语听力：2013-09-29 地平线：黑洞吞噬—5

But that is not the only surprise. People began to realize that these tiny star-like things or they looked like stars are actually putting out as much energy as a hundred of galaxies. And they didnt look like a galaxy at all. The paradox was how some

英语听力：2013-10-02 地平线：黑洞吞噬—6

The mystery of what could count for the quasars' extraordinary brightness was the hot topic in astronomy during the 1960s. As astronomers began to grapple with the new enigmatic objects that had been found by the radio telescopes, one astronomer, kee

英语听力：2013-10-04 地平线：黑洞吞噬—7

It suggested a baffling paradox that quasars are really shining black holes, capable of emitting the energy of entire galaxies. But Lynden-Bell then went further. I predicted that there would be these massive objects found in the nearby galaxies. He

英语听力：2013-10-06 地平线：黑洞吞噬—8

But if you look carefully, stars aren't spread smoothly across the whole sky. They are gathered together into a band that loops around the sky which we call the Milky Way. That bright strip across the sky with its extraordinary abundance of stars and

英语听力：2013-10-09 地平线：黑洞吞噬—9

At last, astronomers had a map of our galaxy. A panorama of the Milky Way, it would never be possible to see from Planet Earth. 27,000 light-years from our solar system is the centre of our galaxy. If we were ever going to have a chance of seeing a b

英语听力：2013-10-11 地平线：黑洞吞噬—10

It's like trying to pick out an individual inside the middle of a busy city, with lights and cars, and things happening all around them. But that wasn't the only problem. Vast, swirling clouds of dust and gas prevent visible light from the centre of

英语听力：探索发现 2013-01-04 冰河新新州 Ice Age Oasis—10

This is the Virginia opossum, a tree dweller found throughout many of the southern states. It's the only North American marsupial. The young are born premature and matured in the mother's pouch. And its only close relatives today are found in Central

英语听力：探索发现 2013-01-02 冰河新新州 Ice Age Oasis—9

The cold climate conifer forests of the north displaced broadleaved woodlands. Plants and animals were gradually pushed south to find a warmer climate. Florida became a refuge from the cold. Down here is where the Ice Age north met the subtropical so

英语听力：探索发现 2013-01-06 冰河新新州 Ice Age Oasis—11

It's likely giant ground sloths used their claws in a similiar way to hook branches and pull them within reach. Like tree sloths, they were vegetarians and probably not fussy about what they ate, chewing their way through leaves, fruits, twigs and al

英语听力：探索发现 2013-01-09 冰河新新州 Ice Age Oasis—12

They can grow more than two metres long and weigh as much as three men. But the giant tortoises of ice age North America were even larger. Florida does have tortoises today, but on a much smaller scale. This is the gopher tortoise. Tortoises are cold

英语听力：探索发现 2013-01-11 冰河新新州 Ice Age Oasis—13

But despite their name, the mighty Everglades did not exist during the ice age. So what did pre-historic Florida look like? There is one place in northern Florida that has revealed more ice age secrets than almost anywhere else, the dark slow-moving

英语听力：探索发现 2013-01-13 冰河新新州 Ice Age Oasis—14

Some of this ice age dung was found beneath the skull in the Aucilla. The dung contained plant remains that tell us what the mastodon was browsing on 13,000 years ago or morea mixture of trees and grasses. This suggests that ice age Florida was drier

英语听力：探索发现 2013-01-16 冰河新新州 Ice Age Oasis—15

Could it be that drastic water shortage was the reason for the mastodons' epic migrations? Another big piece of this puzzle lies far out to sea. This is the ocean floor. But this isn't rock sprouting out at the bottom. It's wood. It's the remains of

英语听力：探索发现 2013-01-18 冰河新新州 Ice Age Oasis—16

This triggered other dramatic changes. As sea levels dropped, so did the inland water tables. Florida's fresh water drained away through the porous limestone rock. Pools dried up and springs diminished. Florida was on the brink of drought. And animal

英语听力：探索发现 2013-01-20 冰河新新州 Ice Age Oasis—17

Today, there is a group of larger visitors here, too. A herd of mastodons led by the matriarch have just returned from their annual migration hundreds of miles to the north. Now the winter drought is over and the spring water has been topped up by re

英语听力：探索发现 2013-01-23 冰河新新州 Ice Age Oasis—18

Meanwhile, the ground sloth, like the mastodons, must eat most of the day to fuel its huge bulk. This may be the ice age, but by midday, temperatures soar, drawing another predator to the spring to drinkthe notorious saber-toothed cat. Most creatures