标签：地球 相关文章
A male polar bear is searching for a mate. Willing females are few and far between. And the sea ice some of which he travels will soon melt and vanished. He's running out of time to find the mate in this frost frozen desert. Ten miles ahead, a single
自然百科2011年
I am standing at the North Pole, the very top of the earth. Up here, it's easy to see why the Polar Regions are so cold. The sun never rises high enough in the sky to warm my back. And those rays that do strike the surface are mostly reflected back f
自然百科2011年
French researchers are predicting doom for Planet Earth. They believe neighboring planets could stray out of orbit and collide with the Earth billions of years from now. The BBC's David Shukman explains their theory. A view of Earth from orbit and a
万花筒2009年
Few have witnessed this moment, for the male, his only tender encounter in an otherwise solitary life. But it doesn't last long. A rival suitor has also caught the female's scent. Courtship has to be put on hold. He must fight for his rights. He sees
自然百科2012年
It's time for the couple to go their separate ways. She will give birth to his cubs alone in nine months time. And he may never see her again. He returns to the frozen ocean, no doubt relieved to resume his solitary ways. And just in time, the ice be
自然百科2012年
For those who can get here in summer, these waters provide a feast of epic proportions. But the good times will be very short, a problem that faces all life in the Polar Regions. Journeying the south across the Arctic Ocean, the first land you/ reach
自然百科2012年
Radiation causes damage at the most fundamental level. It mutates the blueprint of life, DNA. Earth's magnetosphere is our crucial defense. It's so fundamental to our evolution and continued existence that the race is on to understand why it's changi
自然百科2011年
By analyzing thousands of lava samples, geophysicists discover/ that the Earth's magnetic field has reversed over 18,000 times in the last 20 million years. On either side of these reversals is a long period of dramatically reduced field strength. Du
自然百科2011年
In polar regions where the magnetic field is / weakest, auroras glow in the sky. These dazzling displays of colored lights form when solar particles slam into gases in our atmosphere causing them to glow. The stronger the solar wind, the more dramati
自然百科2011年
Scientists believe that the South Atlantic Anomaly, is a sign of a global decline in the magnetic field. Evidence of this comes from a surprising source. Dr. Mimi Hill uses pottery to uncover the secrets of earth's magnetic past. Ancient pots tell us
自然百科2011年
It's clear from the fact that the Martian crust is strongly magnetized, that there must have been a magnetic field on Mars in the past, that the only way we know to magnetize rocks is for them to form in the presence of magnetic field. Why did Mars l
自然百科2011年
The loss of the magnetic field has a catastrophic impact on the planet's evolution. Mars becomes the red planet we see today. If earths magnetic protection continues to fade, would it suffer the same fate? If it vanishes completely, the planet might
自然百科2011年
The randoms of the sea ice are occupied by sun- bathing seals that have been here all winter. But the new arrivals're following the retreating ice edge and they have come here to hunt. Killer whales, the oceans' top predator. Killers are like wolves,
自然百科2012年
Exhausted, it no longer has the energy to pull itself to safety. And the killers are moving in. Game over. Although such team hunts are rarely seen, scientists believe they may be the most complex ever documented in the natural world. They were first
自然百科2012年
The seal is now what the killer wanted, but the hunt is far from over. They need to wrap their prey by the tail while avoiding its snapping jaws. Only them will they be able to pull it down and drown it. Side swipes create farther underwater turbulen
自然百科2012年
The rule is what goes up must come down, but the trouble is nobody knows exactly where the six-ton NASA satellite will crash land. This white blob is the UARS probe as it spins out of control during its descent, the footage was taken by an astronomer
英伦广角
They were travelling on foot and their first sight of this mountains must have been daunting indeed. In front of them stretched one of the world's longest ranges, spanning two thousand miles from one side of the continent to the other. The winds uphi
自然百科2012年
Youve got these beautiful clear glass-like pillars and right next to it, its really delicate. Look at in them, filament is there. As the cave team explore deeper, each chamber reveals ice crystals more strange and spectacular than the last. No one on
自然百科2012年
End of the run. No! Ive got him coming out, I just didnt get him going back in. All right! Below the sea ice, the dive team is setting up an underwater studio. Using a rang of waterproof lights and time-lapse cameras, they hope to capture the growth
自然百科2012年