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This is SCIENCE IN THE NEWS, in VOA Special English. I'm BobDoughty.

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And I'm Sarah Long. This week -- fossils help bring light to amysterious time in prehistoric Africa.

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New findings about air pollution: Could it be worse for the heartthan the lungs?

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And, in the United States, the government acts to ban aweight-loss product.

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Researchers say they have identified animal fossils fromtwenty-seven-million years ago in what is now Ethiopia. The remainsare from the middle of a time called the "missing years" or the"dark period." This is because scientists have so little informationabout the mammals that lived then.

The period began thirty-two-million years ago. Africa and Arabiawere a single continent, a huge island known as Afro-Arabia. Theperiod ended twenty-four-million years ago, after a land bridgeformed with Eurasia.

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John Kappelman is an anthropologist at the University of Texas inAustin and leader of the American and Ethiopian search team. MisterKappelman says eight million years is a long time to lackinformation about a continent. He says scientists have only beenable to guess what happened to African mammals during that period.

The remains found in the Chilga area of Ethiopia offer importantevidence.

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The remains include teeth, skull pieces and other bones. Thescientists found them in a farming area about two-thousand metersabove sea level, in the highlands of Ethiopia. Satellite pictureshelped the researchers decide where to dig. The fossils came fromabout seventy different digs. The magazine Nature published thefindings.

The scientists say the fossils come from before large numbers ofanimals began to arrive in Africa from Europe and Asia. The fossilsalso show that some animals existed millions of years beforescientists had thought.

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The researchers found several kinds of ancient proboscideans.These are animals with trunks. Modern elephants are proboscideans.Scientists have long thought elephants began in Africa. They saythis discovery proves that theory. The ancestors weighed aboutone-thousand kilograms, a lot smaller than African elephants today.

John Kappelman says the elephant ancestors were one of the fewAfrican mammals that survived the invasion of mammals from Eurasia.He says elephants got their start in Africa during theeight-million-year period, and then spread around the world.

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The researchers also found theremains of an ancient animal with two horns on its head, called thearsinoithere. The scientists were excited, because this is theyoungest set of such remains yet discovered. The animal is muchlarger than its ancestors. Earlier forms were about the size ofpigs. But the arsinoithere found at Chilga was about two meters talland weighed more than two tons.

They were similar to the modern rhinoceros. The two are notrelated. In fact, scientists thought arsinoitheres had disappearedfrom the Afro-Arabian continent once rhinos arrived from Eurasia.One researcher says it now appears they did not compete forsurvival.

Scientists say they expect more discoveries to come about themammals that lived during the so-called missing years.

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A study finds that air pollution is worse for the heart than thelungs.The American Heart Association published the findings in itsmagazine, Circulation.

Researchers used information given by more than half-a-millionadults between nineteen-eighty-two and nineteen-ninety-eight. Theinformation is from a continuing study by the American CancerSociety on cancer prevention. The study included people thirty andolder living in cities where officials kept records on airpollution.

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During the sixteen-year period, one in five of the people in thestudy died. The scientists found that heart disease caused aboutforty-five percent of the deaths. Only eight percent of the peopledied from diseases of the breathing system.

The researchers compared the information with air pollutionrecords from more than one-hundred-fifty cities. The scientistscontrolled for things that increase the risk of heart disease, likesmoking and being overweight. Still, they found a stronger linkbetween air pollution and heart disease than respiratory disease.

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Arden Pope of Brigham Young University in Provo, Utah, led thestudy. He says air pollution is not the main cause of heart disease.But, he says, breathing polluted air causes swelling and worsensdisease in the arteries of the blood system. He says this affectsthe ability of the heart to operate effectively. The study alsosuggests that air pollution harms the nervous system, leading toabnormal heartbeat.

The study involved air polluted bysmall particles of soot. Vehicles that use diesel fuel create a lotof soot. So do some factories. But it is also released into the airby burning wood and other substances including animal waste andvegetable oil for fuel.

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Soot was cause for a different concern in another recent study.Scientists with the American space agency, NASA, suggest it as amajor cause of global warming. The NASA researchers say soot may beresponsible for twenty-five percent of global warming observed overthe past century.

With computers they recreated the effects of industrial gases andother influences on world climate. They say carbon dioxide and othergases that trap heat have been the main cause of recent globalwarming, and will remain so. Still, they say soot may be worse thanhas been thought.

The study says the problem is how soot interacts with snow andice.

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Snow and ice have highly reflective surfaces. A lot of thesunlight that hits them is forced back up toward the sky. This helpsprevent melting. But the scientists say the problem develops whensnowflakes pick up fine particles of soot as they fall. The blackcarbon in soot reduces the ability of snow and ice to reflectsunlight. Instead, the black soot absorbs the energy and warmth, andcauses melting.

James Hansen and Larissa Nazarenko of the Goddard Institute forSpace Studies reported the findings. They estimate that sootparticles in snow reduced reflectivity by three percent in northernland areas of the world. Their estimate for the Arctic isone-and-a-half percent.

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The scientists say the soot causes the melting season of glaciersto begin earlier and last longer. This has a large effect, they say,because wet snow is much darker than dry snow. So the problemincreases.

The scientists estimate that soot is two times as effective ascarbon dioxide in changing surface air temperatures. But they saythe good news is that cleaner diesel engines and other technologiesare being developed to reduce soot.

The study is in the Proceedings of the National Academy ofSciences.

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In the United States, the government is acting to ban the sale ofephedra as a product to help people lose weight. Ephedra is a plantthat contains ephedrine and pseudoephedrine. These substances canincrease a person's energy level and cause weight loss. However,officials warn that ephedra also raises blood pressure. Ephedra hasbeen linked to heart attacks, strokes, seizures and deaths.

The secretary of Health and Human Services announced the ban.Tommy Thompson urged people to stop using ephedra even before theban takes effect. He said he did not want to delay the announcement,because people often try to lose weight at the start of a new year.

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The market has grown sharply for herbal products known as dietarysupplements. Companies do not have to prove them safe and effectivethe way drug makers do. In nineteen-ninety-four, Congress limitedthe ability of the Food and Drug Administration to take actionagainst supplements. This is the first ban since then.

The ban will not include the version of ephedra used in medicinesto treat breathing infections. Ephedra has long been used for thispurpose as a traditional medicine in China, where the plant iscalled ma huang.

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SCIENCE IN THE NEWS was written by Caty Weaver and produced byCynthia Kirk. I'm Sarah Long.

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And, I'm Bob Doughty. Join us again next week for another programabout science in Special English on the Voice of America.