How the Grand Canyon (大峡谷) was created remains one of the geology's greatest mysteries. Some evidence suggests that the process was a gradual one in which the Colorado River (which runs through the canyon) slowly cut deeper and deeper into the ground over millions of years. But volcanic rock samples taken from the canyon now suggest that the canyon was down-cut instead.

    Down-cutting is when a flood of water rushes over a landscape (地形) with enough force to cut deeply into the ground and leaves behind a canyon. Such a flood is usually released when a natural or man-made dam (堤坝) bursts.

    Robert Webb, a research geologist, says natural dams seem to have formed and broken across the Colorado River several times during the last million years. The dams were built when lava(熔岩) from the eruptions of nearby volcanoes flowed into the river. The lava hardened into hard rocks and blocked the river, causing it to back up and form a lake. Each time the lake grew so huge that it broke the rock dam, releasing a flash flood that furthered the down-cutting process and deepened the canyon.

    Down-cutting is not just an earthly event. Satellite photos sent back from Mars suggest that the process has happened there, too, say many other researchers.

    The photos, taken by the Mars Global Surveyor, indicate that an enormous lake existed on Mars 3.5 billion years ago. The lake spilled into a large nearby hole. One edge of the hole broke, releasing a flash flood that quickly carved out a grand canyon.

    The existence of down-cutting on Mars is just one more piece of evidence that the cold, dry planet was once warm and wet.

    The light from the campfire brightened the darkness, but it could not prevent the damp cold of Dennis's Swamp (沼泽地) creeping into their bones. It was a strange place. Martin and Tom wished that they had not accepted Jack's dare. They liked camping, but not near this swamp.

    “So,” Martin asked as they sat watching the hot coals. “How did this place get its name ? ”

    “Are you sure you want to hear it ? It's a scary story,” warned Jack.

    “Of course!” cried out Tom. “If there were anything to be scared of, you wouldn't have chosen this place!”

    “Ok, but don't say I didn't warn you,” said Jack, and he began this tale.

    “Way back in time, a man called Dennis tried to start a farm here. He built that cottage over there to live in . In those days, the area looked quite different — it was covered with tall trees and the swamp was a crystal-clear river. After three hard years, Dennis had cleared several fields and planted crops. He was so proud of his success that he refused to listen to advice.

    “ 'You are clearing too much land, ' warned one old man. ' The land is a living thing. It will hit back at you if you abuse it. '

    “ ' Silly fool,' said Dennis to himself. 'If I clear more land, I can grow more crops. I'll become wealthier. He's just jealous!'”

    “Dennis continued to chop down trees. Small animals that relied on them for food and shelter were destroyed. He was so eager to expand his farm that he did not notice the river flowing slowly towards his door. He did not notice salt seeping to the surface of the land. He did not notice swamp plants choking all the native plants.”

    “What happened? ” Martin asked. It was growing colder. He trembled, twisting his body closer to the fire.

“The land hit back —- just as the old man warned, ” Jack shrugged. “Dennis disappeared Old folks around here believe that swamp plants moved up from the river and dragged him underwater. His body was never found.”

    “What a stupid story, ” laughed Tom. “Plants can't …” Before he had finished speaking, he screamed and fainted (晕倒). The other two boys jumped up with fright, staring at Tom. Suddenly, they burst out laughing. Some green swamp ivy (常春藤) had covered Tom's face. It was a while before Tom could appreciate the joke.

    If you could be anybody in the world, who would it be? Your neighbour or a super star? A few people have experienced what it might be like to step into the skin of another person, thanks to an unusual virtual reality（虚拟现实）device. Rikke Wahl, an actress, model and artist, was one of the participants in a body swapping experiment at the Be Another lab, a project developed by a group of artists based in Barcelona. She swapped with her partner, an actor, using a machine called The Machine to Be Another and temporarily became a man. "As I looked down, I saw my whole body as a man, dressed in my partner's pants," she said. "That's the picture I remember best."

    The set-up is relatively simple. Both users wear a virtual reality headset with a camera on the top. The video from each camera is sent to the other person, so what you see is the exact view of your partner. If she moves her arm, you see it. If you move your arm, she sees it.

    To get used to seeing another person's body without actually having control of it, participants start by raising their arms and legs very slowly, so that the other can follow along. Eventually, this kind of slow synchronised（同步的）movement becomes comfortable, and participants really start to feel as though they are living in another person's body.

    Using such technology promises to alter people's behaviour afterwards-potentially for the better. Studies have shown that virtual reality can be effective in fighting racism-the bias（偏见）that humans have against those who don't look or sound like them. Researchers at the University of Barcelona gave people a questionnaire called the Implicit Association Test, which measures the strength of people's associations between, for instance, black people and adjectives such as good, bad, athletic or awkward. Then they asked them to control the body of a dark skinned digital character using virtual reality glasses, before taking the test again. This time, the participants' bias scores were lower. The idea is that once you've "put yourself in another's shoes" you're less likely to think ill of them, because your brain has internalised the feeling of being that person.

    The creators of The Machine to Be Another hope to achieve a similar result. "At the end of body swapping, people feel like holding each other in their arms," says Arthur Pointeau, a programmer with the project. "It's a really nice way to have this kind of experience. I would really, really recommend it to everyone."

    E-mail systems at thousands of companies and government offices around the world were attacked by a virus(病毒)called “Melissa” that disguises(伪装)itself as an “important message from a friend. In spite of a weekend of warnings，more than 50 000 computers at about 100 places around the world have been attacked by the virus，computer security experts said on Monday.

    The virus began to show up last Friday and spread rapidly on Monday by making computers fire off dozens of infected(被传染的)e-mails. Although the virus causes no serious damage to a computer，its effect was far reaching.

    To make matters worse，a similar virus called “Papa” was discovered on Monday. Papa is programmed to send out even more infected e-mails than Melissa.

    The Melissa virus comes in the form of an e-mail，usually containing the subject line“Important Message”. It appears to be from a friend. The body of the e-mail message says，“Here is that document you asked for...,don't show it to anyone else.” Attached(附)to the message is a document file.

    Once the user opens that file，the virus digs into the user's address book and sends infected documents to the first 50 addresses. E-mails from the Papa virus include an attached spreadsheet(电子数据文件)file. When the user opens that file，the virus sends 60 infected e-mails.

    The reason why this is spreading so fast is that you are getting it from people you know. You should never open documents or attachments from people you don't know. People who get an unexpected e-mail with the “important message” subject line should delete it immediately and not open the message.

    With their furry round heads and big black eyes, Zhongzhong and Huahua look just the same as any other monkey. But they happen to be the world's first cloned (克隆的) monkeys.

    Years ago, scientists used cloning techniques to produce Dolly, the world's first cloned mammal (哺乳动物).They now used the same technique to produce the monkeys in China.

    In animal cloning, animals are produced in a lab by using DNA that is taken from the cells (细胞) of a naturally-born animal. To clone Zhongzhong and Huahua, scientists from the Chinese Academy of Sciences (CAS.中国科学院) first removed the nucleus (细胞核) from a monkey's egg cell (卵细胞). They then put another nucleus taken from the monkey's body cells into the egg cell. The newly-formed egg was put into the womb (子宫) of a female monkey. Finally, Zhongzhong and Huahua were born.

    The cloning process is hard, especially removing nucleus. It needs to be done in a fast and precise (精确的) way. The faster you do it, the less damage is done to the egg, according to CAS. Scientist Liu Zhen spent three years practicing removing the nucleus.

    Unlike common monkeys, cloned monkeys have the same DNA as each other. When doing experiments on them, scientists can easily know that certain results are caused by different treatments, rather than different genes.

    According to Sun Qiang from CAS, most drug trials (药物试验) are done on lab mice. However, drugs that work on mice might not work on humans. The two species are very different.

    "Monkeys and humans are much closely related and testing on monkeys is supposed to be as effective (有效的) as testing on humans," Sun added.

I often teach about happiness and what has become clear is this: There are some qualities unhappy people always have. Here are some of them.

 Happy people know life can be hard and tend to live through hard times. They take responsibility for how they got themselves into a mess, and focus on getting themselves out of it as soon as possible. Unhappy people see themselves as victims of life and stay stuck in the "look what happened to me" attitude instead of finding a way through and out to the other side.

    Most happy people believe in the good in people instead of thinking everyone is out to get them. Generally open and friendly towards people they meet, happy people foster(培养) a sense of community around themselves and meet new people with an open heart. Unhappy people are distrustful of most people they meet and don't think strangers can be trusted. Unfortunately, this behaviour slowly closes all chances of meeting new friends.

    Unhappy people believe someone else's good fortune is stolen from their own. They believe there's not enough goodness to go around and always compare others' against theirs. This leads to jealousy(嫉妒). Happy people know that others' good luck and superior circumstances are just signs of what they also can achieve if they try hard enough. They believe in unlimited possibilities and don't get stuck in thinking one person's good fortune limits their possible outcomes in life.

    There's only so much space between the two ears. Unhappy people fill that space with constant worry and fear. Happy people experience fear and worry too, but they make an important difference between feeling it and living with it. When fear or worry crosses happy people's minds, they'll ask themselves if there's an action they can take to prevent their fear or worry from happening and they take it. If not, they realise they're spinning in fear and they lay it down.