Houses fall down. Trees fall over. Large holes form in the ground. Could Alaska be sinking? That's what some villagers in Alaska have been asking themselves recently and scientists think they know why. Warmer temperatures may be causing Alaska's frozen ground to thaw (解冻).

    About 85 percent of Alaska's land surface has permafrost (永久冻结带). Permafrost supports the ground above it—including trees, houses, and roads. But why is the permafrost thawing?

    Some scientists say that human-caused pollution is leading to global warming. And most scientists agree that Alaska has been getting warmer. They say that the warmer temperature is causing permafrost to thaw in some areas. The thawing permafrost can cause problems for people, plants, and animals.

    The collapsing (倒塌) is a problem in the villages in Alaska which are built on permafrost, and some of them may have to move to safer ground, where there is no permafrost.

    The Alaskan town of Glennallen saw its old post office collapse. And, according to James Walters, a permafrost expert at the University of Northern Iowa, house-moving companies have been very busy.

    “Melting permafrost can also destroy trees and forests,” Walters said. “When holes in the ground form, trees fall into them and die. This could turn a forest into a swamp (沼泽), and animals which need the forests will have to move elsewhere.”

    “The melting could cause severe problems.” Walters says, “This could take hundreds of years, but in the end Alaska will look quite different from what it looks like now.”

    If you feel like you've been listening to the same three songs on a loop（循环地）, maybe it's time to discover some new songs. With these apps (almost all of which are free, by the way) and some patience, you might just find your new favorite songs:

Indie shuffle

    Allows you to browse through lesser-known artists' music based on genre（类型）, release date and various other categories（类别）. You can save songs or artists you like and find bands with similar sounds.

Rormix

    Rormix searches your music library to find out what genres and artists you already listen to. Based on its findings, the app suggests music videos you might like just as much. It's an easy way to find new artists without getting too far away from the genres you know and love.

Band of the day

    Provides you with new lesser-known artists and groups to listen to every single day! Download the app, turn on notifications, and you'll get a daily recommendation.

Bandsintown

    If you live for live music, Bandsintown will automatically download your library and suggest concerts you might like based on that list. If a new concert is announced in your area, you will get an automatic e-mail with the details. Basically, you will never miss another show. Here is the best part: You can buy tickets through the app.

Soundcloud

    It is the place to find up-and-coming musicians and remixed singles. Anyone can share and ad music, leading to endless possibilities. The app is a streaming（流媒体）service, online community, and creative outlet. For fans, it makes it possible to keep up with your favorite artists' latest releases.

    Getting rid of dirt, in the opinion of most people, is a good thing. However, there is nothing fixed about attitudes to dirt.

    In the early 16th century, people thought that dirt on the skin was a means to block out disease, as medical opinion had it that washing off dirt with hot water could open up the skin and let ills in. A particular danger was thought to lie in public baths. By 1538, the French king had closed the bath houses in his kingdom. So did the king of England in 1546. Thus began a long time when the rich and the poor in Europe lived with dirt in a friendly way. Henry IV, King of France, was famously dirty. Upon learning that a nobleman had taken a bath, the king ordered that, to avoid the attack of disease, the nobleman should not go out.

    Though the belief in the merit of dirt was long-lived, dirt has no longer been regarded as a nice neighbor ever since the 18th century. Scientifically speaking, cleaning away dirt is good to health. Clean water supply and hand washing are practical means of preventing disease. Yet, it seems that standards of cleanliness have moved beyond science since World War II. Advertisements repeatedly sell the idea; clothes need to be whiter than white, cloths ever softer, surfaces to shine. Has the hate for dirt, however, gone too far?

    Attitudes to dirt still differ hugely nowadays. Many first-time parents nervously try to warn their children off touching dirt, which might be responsible for the spread of disease. On the contrary, Mary Ruebush, an American immunologist (免疫学家), encourages children to play in the dirt to build up a strong immune system. And the latter position is gaining some ground.

    Some inventions are so useful, but seem so simple, that we wonder why no one thought of them long ago. Post-it Notes, the pieces of paper that you can stick almost anywhere and then remove without leaving any sign that they are there, are an example of such an invention.

    Post-it Notes were invented about twenty years ago by Art Fry, a scientist at 3M Corporation. The idea for the product came from an upsetting experience he often had while singing in his church choir. Fry used pieces of paper as bookmarks to mark the places in his book of songs, but these bookmarks were always falling out. He knew he needed a bookmark that would stay where he put it, but that he could remove without damaging the pages.

    Around that time, Fry heard about a new adhesive(粘合剂) that a colleague, Dr. Spence Silver had created. This adhesive was special because it was sticky, but not too sticky. It was strong enough to hold papers together, but weak enough not to tear the paper when it was removed. Fry saw that the new adhesive could help solve his bookmark problem. One morning, Fry put some of the adhesive on the edge of a piece of paper. Just as he hoped, it made a perfect bookmark.

    A short time later, Fry realized that his new invention had even more uses than being a great bookmark. He came to this realization when he wrote a note on one of his new “bookmarks” and attached it to a report he was going to give to a colleague. Soon, co-workers were asking Fry for more sample of his invention so that they could use the new type of notes themselves.

    Fry and some other people at 3M believed so much in the new product that they persuaded the company to give away thousands of the sticky pieces of paper for trial use. When some salespeople at 3M went to offices and showed workers just how helpful the new type of notes could be, they immediately received many orders. As more and more people discovered how useful Post-it Notes could be, the product took off.

    It is rightly said one can share any secret with a true friend. He may know your deepest fears and weaknesses and yet will never take advantage of you. However, keeping a friend's secrets to yourself and not telling the world is what makes the bond grow strong and last forever. You need to develop trust and mutual (互相的) understanding before you start sharing secrets with each other. With friends, secret talks never seem to end and it can get really amusing to know what has been going on in your friend's mind.

    There is a certain time in life especially from the teenage years when one starts having a personal periphery (界限) in life and parents are excluded (排斥) from it. It is because there are certain things that they can't understand and we can't discuss with them. That is when friends become the best secret sharers. They are the ones to whom one reveals one's feelings and best kept secrets.

    It is a general belief that only girls share secrets. But boys have their own secrets that they discuss with only closest friends. The secret talks can range (变化) from relationships, talks about fights with parents, secret activities and anything that is not supposed to be known to others! If you think secrets are limited to only teenagers, get your facts right! Secrets can be shared at any age and there is no hard and fast rule that secrets are shared only among youngsters.

    Sharing secrets with a friend is not just fun, but it also helps to develop a lasting trust in one another. Sometimes, sharing secrets will tell you more about the person. You will come to know whether your friend is reliable and trustworthy and whether it is worth sharing your secrets with them. You can call it a test of friendship.