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Lizard hair, tie-dye vitamins, hottest spot on Earth

Q: How does a gecko lizard cling upside down and scoot across something slick, like glass? —Shirley, Panama City, Florida

 A lizard's (Tokay gecko) hairy foot, clinging to glass [Kellar Autumn, Lewis & Clark College, Portland, Oregon]

A: Hair, geometry, and intermolecular force do the trick, says Kellar Autumn, biology professor at Lewis and Clark College and the man who cracked the gecko’s secret. Five hundred thousand tiny hairs blanket the sole of the lizard’s foot. Each hair tip splits into hundreds more and each of those is shaped like a spatula. A wee spatula too small to see with the best optical microscope. Its diameter is less than the wavelength of visible light.

Such microscopic hairs can pry into practically any surface for purchase. At gecko-hair scale, the smoothest glass appears bumpy and pitted. However, the gecko does not use the friction between her foot and the micro pits to stick. Her way is subtler and more powerful.

Instead, she capitalizes on the transient electrical forces between her hair molecules and the molecules of whatever surface she scampers across. She places her foot "palm" first, uncurls each toe like a party favor, sticks each spatula hair into the glass skylight, pushes the spatula flat, and gets the hair molecules so close to the glass molecules that they electrically bond for an instant. The sticking power is 600 times greater than friction.

The temporary bond, due to van der Waals attraction, depends on the shifting dance of electrons about the nucleus. Consider two jammed-together molecules. At any given instant, the electron cloud about a molecule in the gecko’s foot will be more piled up on one side than the other and therefore more negative than usual on that side. The negative charge pushes the electrons in the nearby glass molecule away to its other side and the opposite charges attract each other briefly. This condition oscillates back and forth (resonates), causing the two molecules (foot and glass) to stick together.

She unzips her feet like tape from a ceiling 15 times per second, peeling off and curling up each toe like a party favor coming back to normal. She simply lifts the flattened spatula hair by restoring the angle that the hair shaft makes with the glass to 30 degrees and the hair pops off. That’s geometry.

By the way, Andre K. Geim of the University of Manchester has imitated the gecko’s adhesive and produced one square centimeter of "gecko" tape. When we make enough to cover your hand (200 sq cm)—you can suspend your 90-pound (41 kg) body (sorry, that’s all) from a pane of glass with that one hand.

Someday, a swarm of "geckobots" may climb a burning building searching for survivors or explore Martian cliffs," says Autumn.

Further Surfing:

Kellar Autumn: How geckos stick to walls

Scientific American: Gecko inspired adhesive

Q: What does a vitamin look like? When asked this question, the best I could think of was to write you. —David, Albuquerque, New Mexico

Vitamin E [©1995-2003 by Michael W. Davidson and the Florida State University, used with permission]

A: Beautiful and bizarre. Vitamins are organic molecules (i.e., made of carbon compounds) that form crystals big enough for a digital optical microscope to capture their gaudy structure. Vitamin C looks like wild feathery fans of blue, red, and yellow. Vitamin E appears as a bursting sunflower sending out rays of blue and gold. Vitamin H (biotin) looks like a symmetrical design of lavender flowers.

The crystals interact with polarized white light to make "a beautiful kaleidoscopic spectrum of color," says Michael W. Davidson of the National High Magnetic Field Laboratory.

Further Surfing:

Michael W. Davidson, Florida State University: The vitamin photo gallery

Q: Where is the hottest place on Earth? I'm guessing it's somewhere like the Sahara. What, if any, humans live there and how do they eke out a living? —Tinjoy, Cebu, Philippines

A: The hottest spot is Al-‘Aziziyah, a small town in Libya, a few miles south of Tripoli. On Sep. 13, 1922, here the temperature soared to 136 degrees F (58 degrees C)—the highest ever recorded on Earth.

Al-'Aziziyah, Libya---the hot spot [Map courtesy of www.theodora.com/maps used with permission]

Strangely enough, people do eke out a good living in this North African town a few miles south of the Mediterranean Sea. It is a major trade center of the Al-Jifarah plain, about 200 miles (300 km) north of the Sahara. What’s more, the gray-brown soils of the Al-Jifarah Plain are fertile, though salty from over irrigation.

Most hot places are in deserts (as you guessed) and low land, like Death Valley, California—the second hottest spot and the lowest place (-178 feet, -54 m) in the Western Hemisphere. On July 10, 1913, Death Valley recorded a high of 134 degrees (57 degrees C).

A lowland is hotter because air warms as it descends just as air cools as it ascends.

Less than 100 miles west of the Red Sea, nestled in the Danakil Plain, lies Dakol in northeastern Ethiopia. This place suffers the world’s highest year-round average temperature—94 degrees F (34 degrees C), with zooming highs of 125 degrees F (52 degrees C). The flat, barren African plain—broken by an occasional volcanic cone— stretches like a widening funnel to the sea. The plain drops at places to 380 feet below sea level. Sometimes no rain falls during a year. The parched soil is too poor to farm.

An African desert at sunset [Corel]

The few who live here—the Danakil— make a living prying loose slabs of solid salt from the plain’s salt pans. Others herd sheep, goats, cattle, and camels over the lonely steppes.

Further Surfing:

USA Today weather: Highs and lows

Theodora: maps and flags

Theodora and CIA World Fact Book: Libya

(Answered July 25, 2003)