Why are these scientists smiling? Professors Yet-Ming Chiang, Angela Belcher and Paula Hammond from MIT proudly stand with a battery-building virus they have engineered. The virus is on a glass slide held by Belcher, center.

What do chicken pox, the common cold, the flu, and AIDS have in common? They’re all diseases caused by viruses, tiny microorganisms that can pass from person to person. It’s no wonder that when most people think about viruses, finding ways to steer clear of viruses is what’s on people’s minds.

Not everyone runs from the tiny disease carriers, though. In Cambridge, Massachusetts, scientists have discovered that some viruses can be helpful in an unusual way. They are putting viruses to work, teaching them to build some of the world’s smallest rechargeable batteries.

Viruses and batteries may seem like an unusual pair, but they’re not so strange for engineer Angela Belcher, who first came up with the idea. At the Massachusetts Institute of Technology (MIT) in Cambridge, she and her collaborators bring together different areas of science in new ways. In the case of the virus-built batteries, the scientists combine what they know about biology (the study of living things), technology and production techniques.

Belcher’s team includes Paula Hammond, who helps put together the tiny batteries, and Yet-Ming Chiang, an expert on how to store energy in the form of a battery. “We’re working on things we traditionally don’t associate with nature,” says Hammond.

Professor Angela Belcher shows off the virus-built battery she helped engineer. The battery — the silver-colored disk on the right side of the device — is being used to power an LED.

Donna Coveney/MIT

Many batteries are already pretty small. You can hold A, C and D batteries in your hand and the coin-like batteries that power watches are often smaller than a penny. However, every year, new electronic devices like personal music players or cell phones get smaller than the year before. As these devices shrink, ordinary batteries won’t be small enough to fit inside.

The ideal battery will store a lot of energy in a small package. Right now, Belcher’s model battery, a metallic disk completely built by viruses, looks like a regular watch battery. But inside, its components are very small—so tiny you can only see them with a powerful microscope.

How small are these battery parts? To get some idea of the size, pluck one hair from your head (unless that seems too painful). Place your hair on a piece of white paper and try to see how wide your hair is—pretty thin, right? Although the width of each person’s hair is a bit different, you could probably fit about 10 of these virus-built battery parts, side to side, across one hair. These microbatteries (“micro” means very small) may change the way we look at viruses.

Slimy liquids that pack a punch
The word “virus” comes from a Latin word that means “poison” or “slimy liquid.” Each virus has a name, and the virus used by Belcher and her team is called M13. To humans, the M13 virus is actually harmless. The virus only infects bacteria. Under a powerful microscope, the M13 virus looks like a thread.

A virus usually has two main parts: a shell and genetic material, molecules called nucleic acid, inside the shell. You can think of nucleic acid (which can be DNA or RNA, depending on the virus) as a recipe that tells the virus what to do. Every living cell has a recipe inside—the genetic material inside you, for example, tells your cells how to keep you alive and functioning.

A virus is like a switch. When a virus is by itself, it cannot do anything—it is switched off. Its genetic recipe sits quietly. The virus cannot reproduce, spread or do any harm. A virus becomes harmful only when it gets inside the cell of a living organism—at this moment it switches “on.” For example, if you look at the chicken pox virus under a microscope, it can’t hurt you. But if the virus finds its way into your body, look out—and try not to scratch.

You won’t see it coming: When the genetic material inside this influenza virus gets into your cells, you get the flu. This picture was taken with a powerful microscope.

CDC/ Dr. Erskine. L. Palmer; Dr. M. L. Martin

When a virus attacks a cell, the virus injects its genetic material inside. The viral genetic material takes over the cell, pushing aside the instructions from the cell’s own genetic material. Instead of doing its normal functions, the cell starts to make copies of the virus. In other words, the virus cannot reproduce itself, but it can turn a living cell into a virus-making factory. These new virus particles can break out of the cell and go on to attack other cells. Those cells may make more virus particles. An infection is born.

Viruses only function inside another cell, so are viruses alive? Scientists have debated this question for decades, and your answer depends on how you define “alive.” On one hand, you might say that something is alive because it has genetic material. Human beings and animals, for example, have genetic material. Rocks do not. On the other hand, if you say that something is alive only if it is able to reproduce and store energy, then viruses are not alive because they need hosts. They’re on the line between living and nonliving things in the world—more like zombies than living organisms!

Changing the recipe
Remember that when a virus invades a cell, it forces the cell to start making new virus particles. At MIT, the scientists are turning that relationship on its head. Belcher and her team are able to go inside the virus and change its genetic recipe. With these changes, the scientists turn the tiny foe into a useful friend.

Instead of attacking other cells, the altered virus does something no natural virus would do: It starts to collect little bits of metal on its shell. Soon the virus is covered by a tiny suit of armor. Underneath the metal, the virus is still there. Belcher likens the virus to a scaffolding—the support structure you might see outside a building that is under construction. The virus provides the structure, giving form to the metal parts while the parts are being put together.

The slide in this picture contains the electronic circuitry that Belcher used to test her virus-built battery. The battery is so small you can’t see it, but it’s there.

Belcher Laboratory, MIT

“The virus remains intact, but is completely covered,” Belcher says.

This metal structure plays an important part in the battery. After the battery charges and discharges, she says, the virus itself may break down, but the metal structure will remain.

A battery is made of three main parts: two electrodes and an electrolyte. Electrodes are pieces of metal with electric charges, and an electrolyte is a material between them. You might think of a battery as a peanut butter sandwich, where the metal electrodes are like the bread and the peanut butter is the electrolyte. (For more information, see What is a Battery? below.)

The metal collected by the virus can be used as an electrode. In 2006, the team built only one electrode, but their research has advanced quickly since then. “We have the materials where we can make the full microbattery now as well,” Belcher says. Last year, together with Hammond and Chiang, she showed how the virus-built electrodes can be produced quickly and cheaply, without toxic chemicals. And earlier this year, with another team of engineers, she helped design the other electrode. When Belcher’s team tested the new, complete battery in the laboratory, it performed as well as other rechargeable batteries.

The microbatteries could be used to power a wide variety of tiny electronic devices. “Because [the batteries] are very small, they can be implemented into anything that involves microfabrication,” says Hammond.

In addition to the ever-shrinking world of electronics, the batteries may also play a role in the search for alternative energy sources. One reason we don’t see more electric vehicles on the road is that they require many heavy batteries to operate. If Belcher, Hammond and Chiang’s work is any indication, then lighter, more efficient batteries aren’t too far away. Just think—the batteries in your car may one day be built with help from a virus!

Going Deeper:

Angela Belcher and her team are currently trying to teach viruses to build new solar cells. To keep up with the latest from her lab at MIT, go to http://belcher10.mit.edu/

Paula Hammond’s research group puts together some of the smallest things in the world: http://web.mit.edu/hammond/lab/

Yet-Ming Chiang’s batteries are making the world a greener place: http://web.mit.edu/INVENT/iow/ychiang.html

This cold-tolerant Burmese python, captured in Florida, could possibly survive along the U.S. coasts as far north as Oregon and Delaware.

There may be a strange, slithering invasion coming from the South. Big snakes like anacondas, boa constrictors and pythons now live in the wilds of southern Florida. Although not originally native to the United States, some of them are now being born there. Most were people’s pets (or the offspring of pets) that got too big, leading the owners to release them into the wild. So far, the snakes have stayed put. But there’s nothing stopping them from moving farther north.

According to a new study by government scientists, some species of large snakes could live comfortably in a large part of the United States—eventually sharing space with 120 million Americans. If the snakes ever start to migrate northward, they could find happy homes as far north as the coasts of Delaware or Oregon. And as North America heats up because of climate change, the scientists say, in 100 years the snakes could become common species in states like Washington, Colorado, Illinois, Indiana, Ohio, West Virginia, Pennsylvania, New Jersey and New York.

The report came from Gordon Rodda and Robert Reed at the U.S. Geological Survey, a government agency that studies the studies natural resources—and natural hazards. Rodda and Reed are both scientists and snake lovers. “We can testify to these snakes’ attraction personally,” the scientists say, “as we both have kept pet giant constrictors. We can attest to these snakes’ beauty, companionability and educational value.”

Rodda and Reed compared the climates of the snakes’ native habitats, where they occur naturally, to the climate of parts of the United States. (The climate of an area describes the average weather—including temperature, humidity, wind speed and rainfall.) Their 300-page report showed that the climate of much of the southern United States was a good match for the native habitat of some species of large snakes. These giant snakes could pose a big ecological problem for coastal states in particular.

Most of these snakes can grow to be 6 meters, or about 20 feet, long. (The boa constrictor, which is small by comparison, grows to be about 4 meters long.)

The Burmese python is one of the most difficult to get rid of. This giant snake can live in either tropical areas or places with cooler weather—and in both wet and dry places. In the United States, Burmese pythons have no natural predators (animals that eat the python and keep its numbers down), so they’re free to grow without watching their backs. These snakes have a ferocious appetite, too. They’ve been known to eat leopards, alligators, porcupines, antelope and jackals.

In 2000, the National Park Service captured and removed 2 Burmese pythons. The next year, they removed 3 more. But the numbers have grown fast—this year, they’ve already removed 270. Given this quick increase, removing these snakes probably doesn’t help solve the problem. The USGS scientists estimate there may already be tens of thousands Burmese pythons slithering around southern Florida.

The scientists aren’t sure how to get rid of the snakes. The government could ban keeping these snakes as pets—but that might not make much difference, since there are already so many in the United States. With enough time and money, snake-hunters could try to remove them all—but who wants to go chasing a 20-foot snake?

Or perhaps giant snakes will be the next fad in food—anyone want an “Anaconda burger”?

POWER WORDS (adapted from the Yahoo! Kids Dictionary and USGS.gov)
climate The weather conditions, including temperature, precipitation, and wind, that characteristically prevail in a particular region.

U.S. Geological Survey A science organization that focuses on biology, geography, geology and water, dedicated to the study of the landscape, natural resources, and the natural hazards that threaten us.

anaconda Either of two nonvenomous, semiaquatic snakesof tropical South America that kill their prey by suffocating it in their coils. E. murinus, the giant anaconda, can attain lengths from 5 to 9 meters (16.4 to 29.5 feet).

boa constrictor A large boa (Boa constrictor) of tropical America that has brown markings and kills its prey by constriction.

python Any of various nonvenomous snakes of the family Pythonidae, found chiefly in Asia, Africa, and Australia, that coil around and suffocate their prey. Pythons often attain lengths of 6 meters (20 feet) or more.

habitat The area or environment where an organism or ecological community normally lives or occurs. The place where a person or thing is most likely to be found.

Going Deeper:

Eating lots of junk food may make it get harder to choose healthy food over time.

It sounds like a science experiment designed by Willy Wonka: Take a lot of junk food, feed it to some rats, and see what happens.

Scientist Paul Johnson of the Scripps Research Institute and his team did just that. But their science experiment was no fiction. They had a serious goal: to try to understand how parts of the brain play a role in obesity. (Obesity is the condition of being very overweight, which has been linked to a variety of health problems.)

The scientists observed that the more junk food the rats ate, the more they wanted to eat—a behavior very similar to that of rats addicted to heroin, a dangerous drug. Johnson told Science News the experiment shows that the brain chemistry of obesity and drug addiction may be quite similar.

In their experiment, Johnson and his team studied the “pleasure center” of rats’ brains. The pleasure center is a complicated network of nerve cells. Together, these cells work as the body’s reward system. If the animal exercises or eats, the cells reward the animal by releasing chemicals into the body that make it feel good. And when the body feels good, the animal—or person—will want to do the behavior again.

Pleasure centers can release these chemicals in less healthy ways, too. Drugs like heroin can cause the pleasurable chemicals to be released.

For the experiment, Johnson fed foods like cheesecake, bacon and Ho Hos to one group of rats. These foods are all high in calories and high in fat. Another group of rats received a regular, nutritious diet. The rats that ate junk food started to eat more and more.

“They’re taking in twice the amount of calories as the control rats,” says Paul Kenny, also at Scripps Research Institute. Kenny worked with Johnson on the study.

Kenny and Johnson wanted to know what was going on in the brains of rats that were overeating. To find out, they came up with a simple reward system. They first devised a way to deliver a small electrical charge to the rats’ brains. This electrical charge would stimulate the pleasure centers to release pleasure-causing chemicals. The rats could control how much stimulation—and how much pleasure—they received by running on a wheel. The more the rat ran, the more pleasure it received.

The rats that had been eating junk food started running more and more. This behavior suggested that the junk-food–eating rats needed more brain stimulation to feel good compared with rats on a normal diet. In other words, their pleasure centers were becoming less sensitive and the junk food didn’t make them feel good unless they ate more and more. The same process happens in the brains of drug addicts. As the pleasure center becomes numb, the addict has to consume more of the drug to feel good.

“They lose control,” Kenny says. “This is the hallmark of addiction.”

Kenny and Johnson also found out that the effects are hard to reverse. After they took away the junk food and offered the rats a nutritious diet, the fat rats refused to eat. “They starve themselves for two weeks afterward,” Kenny says.

Experiments like this one could help scientists understand how chemicals in the brain contribute to obesity. With that information, they may be able to help people avoid obesity—and all of its health problems—in the first place. Not bad for a bunch of rats with Ho Ho’s in their paws.

POWER WORDS

stimulate To increase temporarily the activity of a body organ or part.

obese   Extremely overweight.

nerve cell   The body of a neuron without its axon and dendrites.

chemical A substance with a distinct molecular composition that is produced by or used in a chemical process.

Going Deeper:

The cells in Drosophila melanogaster that produce pheromones are located in the abdomen. Here, the cells are marked by a green fluorescent protein.

View a video of fruit flies displaying unusual courtship behavior.

Fruit flies linger over a bowl of rotting fruit. To untrained eyes, the flies may look like a swarming nuisance, but scientists have found that flies’ swoops and buzzes are ways to send signals through the crowd. Another, less obvious way these insects communicate is through chemical signals called pheromones. (It’s easy to think of these chemical signals as being similar to smells.)

Scientists have long known that pheromones may play an important role in reproduction — certain pheromones may attract a potential mate, for example. But in a surprising new study, scientists found that male fruit flies are particularly attracted to other flies — male and female — that don’t put out any pheromones at all.

The researchers also found that fruit flies without pheromones are attractive to males of other species. This research suggests that pheromones may be even more complicated — and important — than scientists thought. Besides telling other insects to come a little closer, pheromones may also be used to say, “Back off!” That message is important for keeping up barriers between species.

There are many different types of fruit flies, no matter how similar they all look as they swarm over a rotting tomato. Scientists have wondered how fruit flies can tell each other apart. Appearance may play a role. So may sound — the mating song of each different kind of fruit fly is different, for example.

Scientists suspect pheromones may also help fruit flies find potential mates of the same species — but there are 30 or more pheromones to choose from. In the new study, which was led by Joel Levine, the scientists wanted to figure out what messages the different flavors of pheromone were each sending. Levine is a neurogeneticist at the University of Toronto at Mississauga. (Neurogenetics is the study of how genes affect the development and function of the brain and the nervous system.)

His team genetically altered fruit flies so that the flies no longer made pheromones. Then the researchers watched the mating behavior of the insects, and observed that males went after the flies that didn’t have pheromones.

“Males are only after one thing. They want to mate,” Levine told Science News. Females, on the other hand, preferred males with pheromones to the males without. “She will not go for the guy who has no odors,” Levine said. He and his team also used the scentless flies as a starting point for other experiments. They were able to identify one particular pheromone, for example, that kept flies of different species from breeding.

These chemical signals help flies tell males from females, and help tell members of different species from each other. The new research suggests that pheromones may be more important than sight or sound in that crowd of flies hovering over the fruit bowl. “We expected the chemicals would play a role,” Levin said, but “we had no reason to think that the effects we saw would be so strong.”

Strange Attraction from Science News on Vimeo.

In the absence of pheromones, flies engage in unnatural courtship behavior. In this movie, two males attempt copulation with each other’s heads.

Credit: Jean-Christophe Billeter et al, Nature 2009

Going Deeper:

Studies with mice have shown how the same cells on the tongue that taste sourness also detect fizzy flavors.

What does fizz taste like? In bubbly beverages like soda or champagne, tiny bubbles give the drink a lift — and have a distinct taste. Scientists have long wondered how we taste these bubbles. In a new study on mice, scientists have connected that fizzy-taste sensation to the ability to taste sourness.

Scientists previously thought the taste of bubbles comes from the bubbles bursting on the tongue — but that idea may have to change, says Charles Zuker. A neuroscientist, or a scientist who studies the brain and nervous system, Zuker is now at Columbia University in New York. He and his team of researchers studied the nervous systems of mice to understand how the tongue tastes carbon dioxide, which is the gas that makes up the bubbles.

In the experiment, five different groups of mice were genetically engineered to be missing one taste sensation. (“Genetically engineered” means the researchers were able to turn off the switches for certain tastes by altering the responsible genes.) The mice in one group were bred so that they could not taste sweet. In another group, the mice could not taste sour. In the other three groups, the mice could not taste umami, or salty or bitter.

When the scientists gave carbon dioxide gas to the mice, the nervous systems of the rodents in four groups responded to carbon dioxide. But for mice that could not taste sour, their nervous systems did not show any sign of tasting carbon dioxide.

This tipped off the researchers to the connection between sourness and bubbles. When the scientists turned off the sour taste in the mice genes, they also turned off the ability to taste carbon dioxide.

The scientists then zoomed in on the sour taste. Animals like mice or human beings are able to detect different tastes by using taste buds, located near the surface of the tongue. A taste bud is a group of 50 to 150 cells called taste receptors. (Under a microscope, this bundle of cells looks a little like a big bunch of bananas.) The tips of the taste receptor cells pick up tastes in the mouth, and then send that information to the brain.

When they studied the cells that detect sourness, Zuker and his colleagues found a protein, attached to the sour-sensing cells, that is crucial to the process of tasting carbon dioxide. When carbon dioxide comes into contact with this protein, the protein knocks off particles called protons. These protons, in turn, stimulate the sour cells.

So when a mouse — or person — drinks a fizzy drink, there’s a one-two punch. First, the protein knocks off protons. Second, the protons stimulate the sour-sensing cells —and the brain says, “Hey! That’s a taste!”

That may seem like a lot of work to get from a can of soda to a taste — but the science of the senses is anything but simple. Taste “is a very challenging system to study,” Alexander Bachmanov, a scientist at the Monell Chemical Senses Center in Philadelphia, told Science News. “Everything is very small but very complex.”

POWER WORDS (adapted from the Yahoo! Kids Dictionary)

nervous system The system of cells, tissues and organs that regulates the body’s responses to internal and external stimuli. In vertebrates it consists of the brain, spinal cord, nerves, ganglia and parts of the receptor and effector organs.

neuroscience Any of the sciences, such as neuroanatomy and neurobiology, that deal with the nervous system.

proteins Molecules that contain carbon, hydrogen, oxygen, nitrogen and usually sulfur. Proteins are fundamental components of all living cells and include many substances that are necessary for the proper functioning of an organism.

carbon dioxide A colorless, odorless, incombustible gas formed during respiration, combustion and organic decomposition and used in food refrigeration, carbonated beverages, inert atmospheres, fire extinguishers and aerosols.

Going Deeper:

Columbia mammoths, which were relatives of woolly mammoths, roamed as far south as the Black Rock Desert in Nevada, where this fossil was found. The fossil was excavated under the direction of Stephanie D. Livingston, then of the Desert Research Institute

People have been fascinated by woolly mammoths for a long time. Before people even knew how to grow crops or make things from metal, they were decorating their walls with pictures of mammoths. Scientists have found an ancient figurine of a mammoth that was carved from a mammoth tusk in Germany 35,000 years ago. And in a cave in France around the same time, someone drew a picture of a mammoth.

But over time, people stopped drawing mammoths because no more were left. The last known mammoths lived on Wrangel Island in Siberia 3,700 years ago, at the end of a time period called the Pleistocene epoch.

Scientists have long wondered why the mammoths disappeared. Cave paintings of mammoth hunts make it clear that humans killed some of the giant animals, but now scientists are learning that different groups of mammoths went extinct at different times in different places. And it took more than just people to kill them off — changes in climate and maybe even a comet from space were also to blame.

The kind of woolly mammoths that people drew was as tall as an elephant and lived in big groups. They roamed cold northern regions around the globe from about 150,000 years ago until they went extinct. They had three inches of fat beneath their skin to keep them warm. Long, shaggy hair helped keep them warm, too. The Northern Hemisphere during the age of mammoths was covered in steppe-tundra, which is a cold, dry habitat containing scattered patches of herbs, shrubs, scrubby trees and grasses, all of which the mammoths ate. Their tusks, bigger and more curved than those on elephants, probably helped them move snow to find food. When a person stood near a mammoth, could we blame them for awe? No wonder people drew mammoth pictures on cave walls.

But people were thinking about mammoths as more than models for art. Archaeologists—scientists who study ancient cultures by looking at what they leave behind—have discovered that people used mammoth bones to make tools. They used mammoth ribs to build houses. People probably ate mammoth meat and wore mammoth skins. Some people depended on mammoths for their survival.

As humans spread across Europe and Asia 40,000 years ago, they increased in number and honed their hunting abilities. During the same period (from 40,000 years ago to 3,700 years ago), mammoth populations declined and then went extinct. Beginning in 1860, scientists argued that mammoths vanished because people hunted them to extinction. Over-hunting was also blamed for the extinction of woolly rhinoceros, mastodons, cave bears and other mammals. This idea was so common that some people called it “the favorite hypothesis.”

A hypothesis is a proposal that predicts cause and effect. The “favorite hypothesis” suggested that human hunting caused mammoth extinction—but it wasn’t the only hypothesis explaining the mammoth’s demise.

In the 1800′s, scientists didn’t know what the climate was like when mammoths roamed the
Earth, but that has changed. Today, scientists look at records from deep-sea drilling and ice cores from Antarctica and Greenland. By studying the minerals and gases that were trapped in these cores long ago, they can tell what the climate was like in the past. They also look at pollen and plant fossils from all over the world to see what kinds of plants were able to live in different places in the past. Scientists now know when the mammoth’s world was cold (about 8˚C, or 46˚F, in the summer months), dry, and covered with ice sheets. They also know when it was a bit warmer (about 15˚C, or 59˚F, in the summer months) and wetter.

The steppe-tundra habitat favored by mammoths doesn’t exist today. Because woolly mammoths went extinct when ice sheets became rare and the world became warm and wet, some scientists hypothesized that changes in long-term patterns of weather, called climate change, caused mammoths to die.

Last year, a group of scientists from the Museo Nacional de Ciencias Naturales in Madrid, Spain wanted to know what killed the mammoths—and unlike scientists before them, they had data on how much steppe-tundra existed over long periods of time. They also had data on where woolly mammoth bodies had been found, and where people lived between 126,000 years ago and 6,000 years ago. Even though the human populations increased at the same time that the climate warmed and the steppe-tundra habitat vanished, the scientists were able to determine which change caused the mammoth extinction.

Twice in the history of mammoths, their steppe-tundra homes almost disappeared. The first time it happened, starting 126,000 years ago, mammoths nearly went extinct—but they recovered. The second time it happened, starting 6,000 years ago, mammoths actually went extinct. How come the mammoths died off the second time but not the first?

The first time the steppe-tundra habitats receded, humans were not fully modern. They did not have art or advanced tools. They probably couldn’t hunt something as big and intelligent as a woolly mammoth, the scientists think. Humans didn’t have the technology to survive in the very cold places woolly mammoths liked best.

By the second time steppe-tundra habitats receded , humans had changed. Through the use of more complex clothing and housing, people could survive in the cold climates favored by mammoths. Also, people had invented complicated tools, like spear-throwing devices, which allowed them to hunt more dangerous animals. We know people hunted mammoths because mammoth bones have been found with spear holes in them.

Woolly mammoths marching across the steppe-tundra.

Mauricio Anton

The scientists from Spain suggest that climate change pushed woolly mammoths into smaller and smaller patches of steppe-tundra habitat. Humans, with their increasing numbers and new hunting technologies, finished them off.

That explanation may be satisfying, but there’s a problem, or at least a complication: mammoths weren’t the only species to go extinct during that period. At least 35 kinds of North American mammals, including camels, ground sloths, horses and mastodons, died off along with the mammoths.

Scientists have a hard time imagining that human hunters killed everything. According to Donald Grayson, an anthropologist at the University of Washington in Seattle, “One huge problem with the idea that people hunted all the late Ice Age North American mammals to extinction is that although at least 35 kinds of large mammals became extinct at this time, we can only show that humans hunted two of them—mammoths and mastodons.”

Because the over-hunting hypotheses could not be the only explanation, a group of 26 scientists from all over the world looked to the sky. Could a comet have changed North America and killed the mammals?

Richard Firestone, lead scientist and chemist from Lawrence Berkeley National Laboratory in California, describes one possible scenario: “When the comet exploded in the air over the Great Lakes, there was a loud roar, a flash of light and heat hotter than the sun. A great wind of dust and debris followed, rolling across North America to the Atlantic and Pacific Oceans. It churned up the landscape and choked the animals. Hot ash fell across the land, causing vast forest and grass fires. The sky went dark for months until the dust settled.”

Led by Firestone, the team of scientists looked for evidence of a comet. Impacts from comets often are associated with tiny diamonds called nanodiamonds. Comets can bring these diamonds to Earth, and the heat caused by impact can also change graphite in the earth into nanodiamonds. The scientists believe they found nanodiamonds caused by an impact around 12,500 years ago. Such an impact might have helped shrink the amount of steppe-tundra available for mammoths.

Like many hypotheses about extinctions, the comet hypothesis doesn’t explain everything. If a comet exploded in North America, and it was big enough to cause global climate change, then the impact crater should be visible. None is. Of course, that doesn’t mean some intrepid explorer won’t find one.

Most likely, no one thing alone wiped out all of the mammoths. Perhaps a comet destroyed some of the mammoth’s habitat, and hunters killed many of the animals that were left. A small number of mammoths held on in other areas, like on Wrangel Island, only to eventually die off later

People were thinking about woolly mammoths 30,000 years ago, and they are still thinking about them now. People will probably be thinking about woolly mammoths for years to come. The icy, dry world filled with hairy giants has melted away, but it lives on in laboratories—and our imaginations.

Word Find: Woolly Mammoths

An artist’s interpretation shows how a 4.4-million-year-old female Ardipithecus may have looked.

Her scientific name is Ardipithecus ramidus, and scientists call her Ardi for short. She is ancient — her bones are 4.4 million years old — and is making scientists think about the distant past in a whole new way.

Ardi is an example of an extinct species that may help scientists understand how human beings evolved the way we did. She is a hominid, which means she belongs to the same evolutionary family as people. It’s not clear whether Ardi was a direct ancestor of humans.

Scientists have just published more than a dozen studies on Ardi’s species — and this is just the first wave. Ardi’s skeleton is so surprising that “no one could have imagined it without direct fossil evidence,” says Tim White, an anthropologist at the University of California, Berkeley, who has studied Ardi. (An anthropologist is a scientist who studies human beings and their ancestors.).

Ardi first started to show up in 1992, when scientists found her fossilized teeth in Ethiopia. In 1994, her hand bone was found. For three years after that, scientists worked to remove more of her skeleton, including her arms, hands, pelvis, legs and feet. She was believed to be female because she had a relatively small skull and small canine teeth. Between 1981 and 2004, scientists removed other skeletons of other individuals of the same species from the same area. They also removed fossils of other animals and of plants.

White says Ardipithecus looks different from any living primate, so it’s hard to get an idea of Ardi’s appearance by looking at modern primates such as monkeys or apes.

Some scientists have believed that the common ancestor of people and apes resembled a chimpanzee, but Ardi shows that idea may not be true. Ardi’s partial skeleton that scientists have found shows that she could walk upright and easily climb trees and move along branches — traits more easily identified in monkeys or apes. It also shows that Ardi probably couldn’t swing from branch to branch.

“It now seems that the last common ancestor of chimpanzees and humans was much less chimplike than previously thought,” says Alan Walker, an anthropologist at Pennsylvania State University in University Park.

White and his team think Ardi probably stood almost four feet tall and weighed about 110 pounds. This means Ardi is significantly larger than Lucy, a partial skeleton from a different species that lived on Earth 3.2 million years ago. Lucy was also found in Ethiopia. Even though Lucy and Ardi came from different species, they are probably related. Scientists may be able to use information from Ardi’s discovery to learn more about how Lucy’s species evolved.

Owen Lovejoy, an anthropologist at Kent State University in Ohio, also thinks scientists can learn a lot from Ardi’s teeth. He says small canines — especially in the males of the species — suggest that the males rarely fought. Male apes with large canines often show their teeth when they’re fighting over females.

In Ardi’s teeth, Lovejoy sees the beginning of an evolutionary process that led to human beings. “This is one of the most revealing hominid fossils that I could have imagined,” he says.

Going Deeper:

Tamiflu, the primary flu-fighting drug, is getting into surface waters where ducks and other water birds may pick it up. If the birds are carrying flu viruses, which many normally do, those viruses may develop a resistance to the drug, scientists now worr

What if the solution to one problem causes other problems down the road? That may be the case in the ongoing struggle to fight the flu. Flu season is almost here, which means more and more people may be taking Tamiflu in the months ahead. Tamiflu is a popular anti-flu drug that treats both seasonal flu strains and the new H1N1 flu, an unpredictable disease better known as swine flu.

But this increased use of Tamiflu may be introducing new problems. A team of Japanese scientists recently studied three rivers in Japan and found them to be contaminated with Tamiflu’s active ingredient, oseltamivir carboxylate or OC. They found the same contamination in the water discharged from local sewage plants, water that ends up in those rivers. People excreted the drug in their urine, and water discharged from the sewage plants carried it to the rivers.

Sewage treatment plants are designed to remove germs and solids from the wastes dispensed by household toilets, but many drugs can get through. OC is one of those escaping drugs.

OC in the water may be a serious problem for birds — and for people. Here’s why: The flu, short for influenza, is caused by a virus, a tiny organism that invades living cells and turns them against the body. There is not one flu-causing virus; there are many. These many viruses are constantly evolving, or changing in order to survive. They find new ways to infect people and animals, and every year new kinds of flu show up. Birds are natural carriers of many flu-causing viruses.

If a bird drinks water polluted with OC, that bird may be able to fight off the types of flu that Tamiflu treats. As a result, new flus — flus that can’t be cured by Tamiflu — may start to develop in the bird. Once a drug-resistant flu grows in the bird, that bird can pass it on to other animals. This new, stronger flu could eventually start infecting people. And that could mean big trouble, since Tamiflu would not help people fight this stronger flu..

The Japanese study was led by Gopal Ghosh, a scientist at Kyoto University. Ghosh and his team collected water from two places: sewage treatment plants and the rivers that carried away the treated wastewater dispensed by the plants. They first collected samples in December of last year, when the flu season was starting. They collected more water samples in February, when the flu was bad, and collected a third set of samples later.

The scientists found OC in the sewage samples every time. They found a higher concentration in the second set of samples, from February. That’s when the flu was at its worst, and 1,738 cases were recorded in Kyoto. At the same time, in the second set of samples taken in February, the scientists found OC in the river water as well. The OC did not show up in the river in the first and third set of samples.

Scientists have known for years that sewage treatment plants do not remove OC from the water. Jerker Fick, an environmental chemist at Umeå University in Sweden, published a study two years ago that showed that most water treatment plants removed “zero percent” — or none — of the OC. In fact, Fick says, almost all the Tamiflu ingested by a human being will end up in the environment as OC.

And when the OC comes out of the sewage treatment plants, the birds will be ready. Ducks, for example, love to swim in the warm waters just downstream of those plants during the coldest months — during flu season. “I saw it myself,” Fick says.

POWER WORDS (from the Yahoo! Kids Dictionary)

flu or influenza An acute, contagious, viral infection characterized by inflammation of the respiratory tract and by fever, chills, muscular pain and prostration.

concentration The amount of a specified substance in a unit amount of another substance. The Ghosh study determined how many nanograms (one billionth of a gram) of OC was in a liter of the water they sampled.

virus Any of various simple submicroscopic parasites of plants, animals and bacteria that often cause disease and that consist essentially of a core of RNA or DNA surrounded by a protein coat.

Going Deeper:

Scientists are trying to figure out whether it’s safe for kids to talk on cell phones. Credit: atbaei/iStockphoto

About 4 billion people use cell phones, but are they safe? Keep listening—scientists around the world are exploring this question right now. In the meantime, governments are suggesting that people try to limit exposure to radiation from the devices. “Better safe than sorry,” says Siegal Sadetzki, a physician in Israel who studies the health risks of cell phones.

Cell phone users can cut down on radiation exposure by only using the phone when the signal is strong. Another way to reduce exposure is to keep some distance between the phone and the ear.

The phones work by changing the sound of your voice into a radio wave, which it then sends out through an antenna. The phone uses the antenna to receive radio waves, which it then changes into sound waves that a user can hear. These radio waves are a form of radiation, which may be absorbed by tissues in a user’s head, if the phone is close enough.

Most of the scientists who are studying the health effects of cell phones are working in countries other than the United States, but that may change. The United States Senate has recently begun to investigate American research—which may affect 270 million users in the U.S.

Right now, evidence from scientific studies around the world is not strong enough to show a link between cell phone use and disease.

“The currently available scientific evidence about the effects of radiation emitted by mobile phones is contradictory,” says Dariusz Leszczynski, a scientist at Finland’s Radiation and Nuclear Safety Authority, in Helsinki. “There are both studies showing effects and some studies showing no effect.”

If scientists were able to show a link, then cell phones would be sold with a warning label. Scientists like Leszczynski, however, think it’s unwise to think of cell phones as 100 percent safe. Instead, he and his organization recommend that children not use cell phones because the radiation can reach further into their brains than it does into the heads of adults. They also recommend texting rather than talking—to keep the phone away from the head.

In France, the health ministry has been making similar suggestions to keep children off the cell phone. In Israeli, the government recommends that people use speakers or other hands-free devices to keep the phone away from the head. The Environmental Working Group, an advocacy organization in the United States, recommends that people buy low-radiation phones.

Some scientific studies do suggest a link between health problems and cell phone use. Last year, Sadetzki and her group found that heavy cell phone users had a 50 to 60 percent increased risk of a certain type of tumor. Sadetzi says that one reason studies may now be showing risk is that widespread use of cell phones didn’t begin until about 15 years ago. And it may take decades for disease to develop.

She says cell phones are here to stay, but “the question that needs to be answered is not whether we should use cell phones, but how.”

POWER WORDS

radiation The process of emitting energy in the form of electromagnetic waves

antenna A transmitter or receiver of electromagnetic energy, especially microwaves or radio waves.

radio waves An electromagnetic wave within the range of radio frequencies.

Scientists have discovered a small amount of water on the moon. Credit: Luc Viatour

This just in: There’s water on the moon. Scientists have suspected as much for several years, but a group of recent studies give the best evidence yet. Earlier studies suggested the water was frozen in icy patches at the moon’s poles, but these new studies suggest there’s a tiny amount of water all over the moon, more than scientist had believed. The new studies have found signs of water both on the moon’s surface and in its interior.

“This is the first detection of water on the moon and we see it all over, not just in the polar regions,” says Roger N. Clark of the U.S. Geological Survey in Flagstaff, Ariz. Clark worked on two of the new studies.

It’s not much water, though. There’s still no swimming or surfing on the moon, and stargazers shouldn’t go looking through telescopes for lunar waterfalls or raging rivers. In fact, this amount of water would be much too small for astronauts on the moon to see. In the words of the poet Samuel Taylor Coleridge, one might say there’s “water, water everywhere,” but not “a drop to drink.”

On the moon’s surface, the concentration of water averages about 1000 parts per million—roughly the same as if one cup of water were poured into a typical playground sandbox. That water acts like dew on Earth: The water that forms on the surface quickly disappears later in the same lunar day. (A “lunar day” is a day on the moon, which lasts about four Earth weeks.) The water disappears by becoming a gas, through the process of evaporation. This cycle of formation and evaporation happens every day.

Clark, the scientist at the U.S. Geological Survey, says he and his team first found some of the newly reported evidence of water on the moon in 1999. In that year, the Cassini spacecraft took measurements of the moon as it flew by on its way to Saturn. (Cassini reached Saturn in 2004 and since then has been beaming back beautiful pictures of Saturn’s rings.) When Clark studied the data sent back by Cassini, he first saw the signs of water.

Clark was excited about that first discovery, but he wanted to make sure other scientists could also find water. “The detection was so fantastic,” he says, “I felt we needed confirmation.” His conclusion—that there was water on the moon—needed verification.

Verification is an important part of the scientific process—once a scientist makes a discovery about the natural world, other scientists must be able to do the same experiment and get the same results. If other scientists cannot get the same results, the original conclusion may need revision.

Confirmation of Clark’s original findings finally came earlier this year from two other spacecraft that also took measurements of the moon’s surface. One of these, NASA’s Deep Impact spacecraft, has been used to study comets. The other, called Chandrayaan-I, is the first mission to the moon from India. Hydrogen—one of the components of water—has also been found by the Lunar Reconnaissance Orbiter, a spacecraft that orbits the moon taking measurements.

Jessica Sunshine of the University of Maryland in College Park led the study of data from Deep Impact. Sunshine has an idea for how water forms on the moon’s surface. Water is made of hydrogen and oxygen. Some minerals on the moon’s surface are already rich in oxygen, and hydrogen may come from the solar wind. (The solar wind is an invisible stream of radiation that comes from the sun.) Later, heat from sunshine may vaporize the newly formed water.

In addition to finding water on the surface of the moon, scientists have also found water in the moon’s interior. Minerals there may have an even higher concentration of water than on the surface. An understanding of the moon’s interior can help scientists figure out how the moon came into existence.

On October 9, a NASA spacecraft called LCROSS is supposed to crash into the moon, and scientists hope that the dust cloud from the collision will further improve their understanding of lunar water. “Our picture of a bone-dry moon is clearly in need of updating,” says Robin Canup, a scientist at the Southwest Research Institute in Boulder, Colo.

POWER WORDS

evaporate/vaporize To convert or change into a vapor.

mineral A naturally occurring, homogeneous inorganic solid substance having a definite chemical composition and characteristic crystalline structure, color, and hardness.

verification A confirmation of truth or authority, or the evidence for such a confirmation, or a formal assertion of validity.

solar wind A stream of high-speed, ionized particles ejected primarily from the sun’s corona.