Now, a team of scientists has found the oldest-known biological molecules inside some of those briny salt-water pockets. The team analyzed samples of salt mined deep underground in southeastern New Mexico. They found molecules of cellulose—the tough, fiber-like molecule that makes up plant cell walls. Algae and some bacteria also make cellulose. Because the molecule is made by living organisms, its presence in the salt deposit is evidence that some kind of ancient organism made the cellulose trapped inside.

Scientists found this ancient mat of tiny, threadlike cellulose fibers in 253-million-year-old salt deposits deep below the New Mexican desert. Each of the cellulose fibers, shown here through a microscope, measures between 5 and 16 nanometers (a human ha

Jack D. Griffith/University of North Carolina in Chapel Hill

To identify the cellulose molecules, the scientists removed material from inside the salt-water pockets. They placed the material in a hot solution of two chemicals, sodium hydroxide and sodium borohydride. This harsh solution dissolves all known biological materials except cellulose. The material didn’t dissolve, telling the scientists that the material in the salt deposits was most likely cellulose.

As an additional step, the researchers also mixed the material with a cellulose-digesting enzyme. This time, the material quickly dissolved. Taken together, these results give strong support to the scientists’ conclusion that the salt-water pockets contain cellulose.

The research team used radioactive dating to determine that the salt crystals—and the cellulose inside of them—formed more than 250 million years ago. In all that time, the crystals have hardly changed.

The findings tell the research team that ancient salt deposits like these might be ideal for preserving ancient molecules, which are signs of early life. A challenge to researchers looking for evidence of long-extinct living things is that the molecules that made up their bodies usually broke down because of exposure to sunlight, wind, water or other living things that digested them.

The salt-pocket cellulose tells another story: Buried deep below Earth’s surface, the encased cellulose molecules are protected from the sun’s harmful ultraviolet radiation and other harsh conditions. Such salt-water pockets might be ideal places to look for signs of long-gone life forms—both here on Earth and on other planets.

Scientists in a field called astrobiology are especially interested in these old cellulose molecules. Astrobiology is the study of life in the universe. Many astrobiologists focus on finding the best ways to search for life on other planets, aiming to answer questions about life in space—Does it exist now, and did it ever exist in the past?

It’s a good question, and one that’s hard to answer. After all, where would you start looking on Mars if you wanted to look for signs of life? As it turns out, both Mars and Jupiter’s moon Europa once had oceans—just like the New Mexico desert. Do they have similar salt deposits? No one knows for sure. But if planets and moons do, they might give scientists a good target to look for signs of past life.—Jennifer Cutraro

Power Words

From The American Heritage® Student Science Dictionary, The American Heritage® Children’s Science Dictionary, and other sources.

brine or briny Water containing large amounts of salt.

cellulose A carbohydrate that is the main component of the cell walls of plants. It is insoluble in water and is used to make paper, cellophane, textiles, explosives and other products.

digestion The process by which food is broken down into simple chemical compounds that can be absorbed and used in the body.

enzyme Any of the proteins produced in living cells that act as catalysts in the metabolic processes of an organism.

Europa The sixth moon of the planet Jupiter.

Jupiter The planet that is fifth in distance from the sun. Jupiter is the largest planet in the solar system and has the shortest day, lasting less than 10 hours.

Mars The planet that is fourth in distance from the sun. Mars is the third smallest planet in the solar system and is similar to Earth.

radioactive dating A technique for measuring the age of a material based on the spontaneous breakdown of a radioactive nucleus into a lighter nucleus.

ultraviolet radiation Electromagnetic radiation that has wavelengths shorter than those of visible light but longer than those of X-rays. Ultraviolet light is given off by the sun but is invisible.

Copyright © 2002, 2003 Houghton-Mifflin Company. All rights reserved. Used with permission.

Going Deeper:

Perkins, Sid. 2008. Salty Old Cellulose: Tiny Fibers Found in Ancient Halite Deposits. Science News 173(April 5):213. Available at http://www.sciencenews.org/articles/20080405/fob5.asp .

Cowen, Ron. 2007. A Crack at Llife. Science News 171(March 10):158. Available at http://www.sciencenews.org/articles/20070310/note12.asp .

Pegg, J.L. 2007. An Earthlike Planet. Science News for Kids (May 2). Available at http://www.sciencenewsforkids.org/articles/20070502/Note2.asp .

Travis, John. 1999. Prehistoric Bacteria Revived from Buried Salt. Science News 155(June 12):373. Available at http://www.sciencenews.org/pages/sn_arc99/6_12_99/fob3.htm .

The larvae of an African fly known as Polypedilum vanderplanki live in the bottom of rain puddles in the African desert. When the dry season hits, and their habitats dry up, they can endure an almost complete loss of body water. They can persist in this dormant state, which is similar to a very deep sleep, for up to 17 years.

Just add water, and before long the dead-looking critters are moving and feeding again.

Curled up into a 4 millimeter–long mummy, this fly larva can suspend its life for years, withstanding severe drought and extreme temperatures.

Daisuke Tanaka/National Institute of Agrobiological Sciences in Japan

Most other animals that have been known to freeze-dry—sea monkeys (brine shrimp) and water bears (tardigrades), for example—are microscopic. Biologists have known for years that a sugar called trehalose plays a role in the drought-survival tactics of these species.

In water bears and sea monkeys, small command centers of cells remain hydrated during dormancy. In cells throughout the rest of the body, however, water is replaced with the sugar trehalose.

How does this special sugar allow cells, let alone small creatures, to survive? Scientists have long thought trehalose keeps the cells from falling apart by turning into a glassy state. This state is much like melted table sugar that has solidified into hard candy drops. A series of new studies show that’s exactly what happens in the fly P. vanderplanki.

Takashi Okuda of the National Institute of Agrobiological Sciences in Tsukuba, Japan, and his collaborators collected P. vanderplanki—which look more like mosquitoes than flies—and got them to breed in the lab. This provided a steady supply of young larvae for the scientists to study.

The researchers then used a technology called infrared imaging to visualize and measure the amount of water and heat in the larvae’s tissues. The study showed that the trehalose was uniformly distributed throughout P. vanderplanki‘s bodies.

When the researchers turned up the heat, they found the larvae’s absorption of heat peaked at around 70° Celsius (158° Fahrenheit). That’s the same temperature at which solid table sugar begins to melt. The findings showed that the trehalose sugar had, indeed, been in a glassy state.

A second experiment showed that trehalose sugars had bonded with the cells’ outer layer or membrane. This protected the cells’ insides from extreme distortion during dehydration.

Okuda says he and others would like to steal P. vanderplanki‘s secret to learn, for example, how to store people’s blood in a dried form until it is needed for medical uses such as transfusions. The main challenge, he says, is to get trehalose to penetrate the membranes of red and white blood cells. If this could be done, the dehydration technique could eventually be used to preserve entire organs.

Power Words

From The American Heritage® Student Science Dictionary, The American Heritage® Children’s Science Dictionary, and other sources.

dehydration The process of losing or removing water or moisture.

dormant state An inactive state in which growth stops and metabolism is slowed.

habitat The area or natural environment in which an animal or plant normally lives, such as a desert, coral reef or freshwater lake.

heat absorption The process of taking in heat and holding it. During the day the Earth takes in and stores heat from the sun through absorption.

infrared Relating to the visible part of the electromagnetic spectrum with wavelengths longer than those of visible red light but shorter than those of microwaves.

larva An animal in an early stage of development that differs greatly in appearance from its adult stage. Larvae are adapted to different environments and ways of life than adults and go through a process of metamorphosis to change into adults.

transfusion The transfer of blood from one person to another, often to replace blood lost due to injury or surgery.

Copyright © 2002, 2003 Houghton-Mifflin Company. All rights reserved. Used with permission.

Going Deeper:

Castelvecchi, Davide. 2008. Live another day: African insect survives drought in glassy state. Science News 173(March 29):197. Available at http://www.sciencenews.org/articles/20080329/fob5.asp .

Sohn, Emily. 2005. Putting a mouse on pause. Science News for Kids (April 27). Available at http://www.sciencenewsforkids.org/articles/20050427/Note2.asp .

______. 2004. A dire shortage of water. Science News for Kids (Aug. 25). Available at http://www.sciencenewsforkids.org/articles/20040825/Feature1.asp .

______. 2004. Prime time for cicadas. Science News for Kids (May 19). Available at http://www.sciencenewsforkids.org/articles/20040519/Feature1.asp .

But sugar is high in calories, and eating too much of it can cause weight gain and other health problems. That’s why millions of people drink diet sodas and eat foods that contain artificial sweeteners in place of sugar. These synthetic chemicals taste sweet, but they have no calories.

It can be hard to resist the temptation of chocolate and other sweet treats.

André Karwath/Wikipedia

But are sugar substitutes safe to use? The answer is complicated.

Sweet controversy

For as long as artificial sweeteners have been around, they’ve been surrounded by controversy. Some studies have suggested that they cause cancer, allergies, and other health problems, while other studies question those findings.

It’s also unclear whether eating sugarfree foods can actually help people control their weight. Some researchers even think artificial sweeteners are helping fuel a widespread addiction to sugar.

Regular or diet, drinking lots of soda can fuel a constant desire for sweets.

iStockphoto.com

“The more [sweets] you get, the more you need to feel satisfied,” says David L. Katz, director of the Yale-Griffin Prevention Research Center in New Haven, Conn.

“So, when it comes time for dinner,” he says, “pasta sauce without added sugar tastes bland. When it’s time for dessert, intense sweetness is required” for people to be happy.

Despite the debate, plenty of people continue to down artificial sweeteners. In the United States alone, nearly 200 million people consume sugarfree or low-calorie products, according to the Calorie Control Council, a group that represents the diet-food industry. About half of the people who eat and drink sugarfree products make a habit of it—consuming an average of four such items every day.

People develop lifelong preferences for certain tastes and flavors during childhood, Katz says. So the choices you make now may affect eating habits for the rest of your life.

Acquired tastes

Some flavors, such as spicy and sour, require practice to enjoy, and our tongues are highly sensitive to these tastes. Just a dash of cayenne pepper, for example, can make a dish too fiery for some people to eat. A preference for sweet, on the other hand, comes naturally. Even babies like sugar—and lots of it.

That’s because sugar is a rich source of calories, and calories provide energy. For our ancestors, craving sweet foods was an important way to ensure that they would get enough energy to survive, says Eric Walters, a biochemist at Rosalind Franklin University of Medicine and Science in North Chicago, Ill.

Sugar comes in a variety of forms or flavors—all sweet.

Romain Behar/ Wikipedia

Since more calories mean more energy, our taste buds developed a fairly high tolerance for sugar, Walters says. That means most people can handle—and enjoy—huge doses of sweet stuff.

Artificial sweeteners stimulate the same cells in our tongues as sugar does. Thanks to the substitutes’ chemistry, however, they are hundreds to tens of thousands of times as sweet as sugar. That means that far less of them is required to make something taste sweet.

So, where a 12-ounce can of regular cola contains about 10 teaspoons of sugar, a can of diet cola contains less than a tenth of a teaspoon of the artificial-sweetener aspartame.

Because sugar substitutes work in such small quantities, they add almost no calories to a product. That’s good news to many people on weight-reduction diets.

People with a disease called diabetes also often turn to artificial sweeteners because these products don’t raise levels of sugar in the blood, as sugar does. Diabetics have to be extra careful about controlling blood-sugar levels.

But artificial sweeteners are chemicals, and they’re made in labs. Sugar, by contrast, comes from living plants. Many people are concerned that artificial sweeteners, like some other synthetic chemicals, may cause health problems. Over the decades, the fears have waxed and waned, but questions about their safety are still debated.

Scary sweeteners

Five artificial sweeteners are currently available in the United States (and several more in other countries). Saccharin, the oldest artificial sweetener, was first produced in 1879. It’s sold as Sweet’N Low in the United States. It’s used in diet soda, candy, and other sugarfree products.

Some studies have linked saccharin to cancer in rodents. But other studies have shown that animals must consume the equivalent of hundreds of cans of saccharin-containing soda every day to experience any ill effects.

In the minuscule amounts that people actually consume it, Walters says, “I think saccharin is very, very safe.”

Aspartame (which is marketed as NutraSweet or Equal and appears in products such as Diet Coke and Diet Pepsi) has aroused similar health concerns since it was first produced more than 40 years ago. In the most recent scare, a group of Italian researchers found evidence that rats fed lots of aspartame developed cancer.

People criticize full-sugar sodas and diet versions for different reasons.

David Shay/Wikipedia

A panel of 10 American scientists examined the Italian research and found major flaws. The rats used in the experiments, for example, were sick to begin with. And the researchers didn’t keep good track of exactly how much aspartame each rat consumed.

The U.S. panel also reviewed more than 500 aspartame studies and concluded the substance is safe. The majority of the studies, the scientists found, show that an average adult can eat as many as 19,400 packets of Equal a day without any permanent ill effects.

“I have no question in my mind that it is safe to consume aspartame, and I’d rather consume that than the calories of a full-sugar soda,” says University of Maryland toxicologist Bernadene Magnuson, a member of the review panel. She encourages her kids to adopt the same attitude.

Some scientists and antisweetener activists remain concerned that previous safety studies have been biased in favor of artificial sweeteners. (The U.S. experts-panel study cited above, for example, was funded by a company that produces aspartame.)

“The only ones with the incentive to study [artificial sweeteners] are the companies marketing them,” says Michael Jacobson, executive director of the Center for Science in the Public Interest in Washington, D.C. “If they say it causes cancer, they’re out of business.”

Diet food?

Millions of people have been consuming artificial sweeteners for many decades, and no diseases have broken out as a result. That’s pretty good evidence that these substances are probably harmless to our health at the concentrations we eat them, Katz says.

Still, Katz himself avoids them, partly because he says there’s no convincing evidence that “diet” products are a good diet strategy. In fact, eating artificially sweetened foods may actually sabotage weight-reduction efforts.

Packets of artificial sweeteners sit next to packets of sugar in many restaurants.

iStockphoto.com

In a 2004 study, for example, rats that drank a lot of a saccharin-sweetened drink ended up eating much more other food than did rats that had drunk equal amounts of a beverage sweetened with sugar.

What’s behind the surprising result? Perhaps, Katz says, artificial sweeteners confuse the brain’s ability to connect sweet tastes with the calories in sweet foods. So, rats that eat a lot of sugarfree foods may end up eating more high-calorie foods to compensate. The same might be true of people.

Katz also suspects that bathing the tongue all day in any kind of sweetener—plant based or artificial—only increases desire for supersweet foods. Today, he says, most store-bought salad dressings and pasta sauces contain more sugar per gram than chocolate syrup does. We’ve become so used to the taste of these products that many people prefer them to unsweetened versions. (Artificially sweetened versions of these products are now available too).

Sugar, sugar everywhere . . .

Despite the questions and controversies, artificial sweeteners, like sugar, are more popular than ever. They’re appearing in more and more foods, from ice cream to jellies to cough drops. And the U.S. Food and Drug Administration is reviewing even more sugar substitutes for approval.

The more sugar you eat, the more you probably want.

iStockphoto.com

In an attempt to eat a healthy diet, Katz and his family try to avoid sugar as well as artificial sweeteners. The effort has influenced the taste preferences of his five children.

Because his kids eat so little sugar at home, Katz says, they experience sweetness overload when they eat cake or other sweet treats at a birthday party.

“They take one bite and then look for the wastebasket to spit it out,” he says, “because [to them] it’s sickeningly sweet.”

Going Deeper:

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