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Outside magazine, August 2000
By Stephanie Gregory

Not long ago, lightning hit a small tree next to me, knocking the fillings out of my teeth. How'd this happen?

—S.W. Ochs, Charleston, South Carolina

Consider yourself lucky: You could have been one of the 100-odd Americans killed by lightning each year—or one of a more elite group of survivors whose encounters with 20,000-ampere bolts of current hot-wired their fillings to pick up the transmissions from nearby radio stations. Weird. But while the effects of lightning vary widely, there are only three ways in which the supercharged force can actually hit you: a direct strike, a side flash (when a portion of the charge leaps from its original point of contact to another target within a 30-foot radius), or a ground or step potential (when a bolt hits the ground and the current ripples outward). In your case, the tree probably got the direct strike, and you were zapped by the side flash. As for your dentistry, the bolt's electricity most likely warmed the moisture and metal in your mouth, loosening your fillings like the lid of a jar under hot water. That said, we hope you didn't suffer another troubling lightning-related fate: squelched libido.

How do paragliders read thermals?

—A. McSweeney, Houston, Texas

Some paragliding pilots liken their sport to paddling a Class V river while blindfolded. That's because thermals—those pockets of hot air that amass on the groundand then rise skyward like giant soap bubbles—are fleeting and invisible. Unlike rapids, thermals can't be scouted, much less relied upon to remain constant. Often a thermal will die out midglide, requiring the pilot to hitch a ride on a fresh one if he hopes to spiral higher (18,000 feet is the FAA's limit on all non-commercial flights, but some renegade gliders have been known to soar to nearly 24,000 feet). Dicey, maybe, but therein lies the thrill—and the challenge: To support the 200-plus-pound heft of a paraglider and his equipment, a thermal must rise more than200 feet per minute, though daredevil fliers prefer the "shotgun" variety, which can skyrocket in excess of 3,000 feet per minute. How to determine good air? Bring along a variometer, a minicomputer that straps to your leg and measures changes in barometric pressure and yields readings of relative altitude.The more frequent and forceful the instrument's beeps, the quicker you're gaining altitude—confirmation that you've hit the thermal's sweet spot.

Is it true that it takes air pollution 40 to 50 years to exit the earth's atmosphere?

Marc Oligee, Cincinnati, Ohio

Pollutants such as carbon dioxide and chlorofluoro-carbons (CFCs) can take ten years to a century to soar into the stratosphere, where they're broken down by ultraviolet radiation. This isn't always a good thing: CFCs, for instance, spin off highly reactive chlorine molecules, some of which eat away at the ozone layer. Carbon dioxide, meanwhile, breaks down even more reluctantly; it must rise nearly 60 miles before it can be ripped apart by UV rays into carbon and oxygen. Of course, plants need CO2 for photosynthesis, and oceans absorb it as well. It's a nice give-and-take, until you consider that humans produce roughly 8.5 gigatons (that's 85 billion metric tons) of carbon a year through the burning of forests and of fossil fuels—three gigatons more than our plants and oceans can ingest, thus creating a thickening blanket of greenhouse gases that many scientists blame for global warming. "On a human time scale, this stockpile of CO2 is permanent," says Pieter Tans, a researcher with the National Oceanic and Atmospheric Administration. "We'rewreaking havoc with atmospheric equilibrium."

What's the most aggressive animal on the planet?

Colin Winter, St. Charles, Illinois

Define aggression as the readiness to charge another animal in defense of territory, young, mates, or food, and a variety of species can lay claim to the title. Few creatures can rival the custodial ferocity of a mama grizzly protecting her offspring, and wild stallions have even been known to fracture an interloper's skull with a purposeful kick. But it's with sex that things get really brutish. A male Siamese fighting fish is so possessive of his female that he'll sometimes attack his own mirror image (what he lacks in brains, he makes up for in feistiness). The four- to six-centimeter critter is no less aggressive with a real-life rival. He'll use his tiny, razor-sharp teeth to shred the other's fins and body until the victim bleeds to death. If that's not fierce enough for you, try this: A female fighting fish has a 50/50 chance of being maimed by her savage partner during mating. Hey, love hurts.  

Illustrations: Brian Rea

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