Pearls, rare and lustrous, reveal their underwater secrets
By Louis Porter
American Museum of Natural History
Pearls: A Natural History
|The Biwa pearl mussel from Lake Biwa, in Japan, was once a rich source of cultured pearls until pollution nearly drove the mussels to extinction in the 1990s.|
Photograph courtesy of Jackie Beckett/American Museum of Natural History
The Swedish naturalist Carl von Linné (better known as Linnaeus) is famed for creating a uniform system for defining and naming the genera and species of organisms. But he earned the Swedish noble title von for a more obscure achievement. In the 1750s, Linnaeus became the first person to culture round pearls artificially. The simple method he devised involved cracking open a freshwater mussel and inserting a bead nucleus, which he then suspended from the surface of the shell with silver wire. Pearls,
a new exhibition at the American Museum of Natural History in New York City and at Chicago's Field Museum starting in June, evokes the aura of the gems that captured Linnaeus's imagination. In galleries bathed in muted light and a murmuring sound track of watery effects, pearl-laden jewelry is displayed beside pearl specimens and the shells of the creatures from which they emerged. Various marine and freshwater invertebrates from the vast phylum Mollusca produce pearls. But only mollusks whose shells are lined with mother-of-pearl, most notably some species of saltwater oysters and freshwater clams, produce round pearls with the translucence and luster prized by gem hunters since the Bronze Age.
|This cross section of a pearl, magnified 60 times, reveals the concentric crystalline layers that give the jewel its luster.|
Photograph courtesy of Neil H. Landman/American Museum of Natural History
The origin of pearls was for centuries shrouded in mystery and mythology. "There were theories that white pearls formed during the day, and black pearls formed at night, that pearls came from dewdrops the oysters would catch," says RŸdiger Bieler, a cocurator of the exhibition. By the 18th century, however, scientists aided by the advent of the microscope discovered how natural pearls are actually formed. Typically a wayward food particle becomes trapped between a mollusk's shell and its mantle. The mantle—a fleshy organ that envelops the mollusk's soft, fluid body—secretes layer upon layer of the mineral aragonite, a form of calcium carbonate, and the protein conchiolin. Together these form the composite material known as nacre, from which the mollusk's mother-of-pearl shell and the pearl itself are made. A so-called blister pearl, which is irregularly shaped, results when the intruding object adheres to the mollusk's shell and is enveloped in nacre. But if a piece of the mantle gets pushed or dragged—by a dying shrimp, for instance—into the body of the mollusk itself, the mantle gradually encases the object within a nacreous tomb. Several years later a luminescent pearl is born.
Light reflecting off each of the thousands of concentric layers of aragonite crystal and conchiolin gives the pearl its depth, luster, and value. Museum visitors can view the crystal structure of a pearl at magnifications ranging from 29 to 50,000 times its actual size. As the magnification increases, stacks of flat, six-sided aragonite crystals alternating with layers of conchiolin appear deep inside the pearl's core. It's a sight that would have made Linnaeus's jaw drop. Movies Inner Beauty
A large-format film shows blood, bone, and sinew—the real you By Maia Weinstock The Human Body
Produced by Discovery Pictures and BBC
Directed by Peter Georgi
To the casual observer, riding a bike appears simple. But The Human Body,
a new IMAX-format documentary from Discovery Pictures and the BBC, reveals that the act of pushing those pedals involves an intricate interplay of motion and force. Photographed through an X-ray camera, a bicyclist looks like a Halloween skeleton on uppers as his bones move in remarkable synchrony. Then, viewed through the lens of the world's highest-definition thermal imaging camera, he puts on a psychedelic light show as various tissues throw off visible heat and energy during a tough climb up a hill. The Human Body
utilizes a wide array of visual technologies to showcase the splendor and complexity of the human form. For example, electrical signals zapping across brain synapses and billions of blood cells shuttling through the body's 100 miles of veins, arteries, and capillaries seem far from routine when magnified by the most powerful imaging techniques available. In one of the film's most memorable sequences, viewers are plunged into a freeze-dried human cochlea, seen under a high-powered scanning electron microscope, where hairs 1/10,000 the width of a human strand dance in sync to the vibrations of music.
|Scanning electron microscope images show the fingers of a fetus at eight weeks (left) and 15 weeks (right). The emergence of the fingers takes place as cells between the individual digits die off.|
Photographs courtesy of Discovery Pictures/BBC
Director-producer Peter Georgi offers an astonishingly close look at the inner mysteries of the body. In fact, sometimes the view is a bit too close. After watching food travel from the mouth to the swampy environs of a mucus-lined stomach and into the lower digestive tract, where nasty green bile spills out of a gallbladder like a water balloon that's just been popped, some viewers may feel a bit queasy—especially because the stewed lunch is blown up to the size of a seven-story building. But most sequences are more gorgeous than gross. An eerie trip through the dimly lit chambers of an empty heart, accompanied by the blasting rhythm of its ventricles, will most likely make viewers acutely aware of the pulsing of their own beating hearts. Georgi actually used a pig's stomach and heart for these two scenes—not to mention "the most optically pure endoscope on the planet"—but the porcine organs so resemble human ones that "even physicians can't tell the difference," he says. The Human Body
also takes a wondrous peek at human reproduction, including the union of sperm and egg (to the tune of Marvin Gaye's "Let's Get It On"), the fusion of male and female DNA, the first division of the zygote, the embryo's development, and finally, the baby's emergence from the womb. Child and adult audiences alike will leave The Human Body
in awe of the astounding biological feats they perform without even knowing it. Toys Get Smart
Add a third dimension to your search for knowledge By Fenella Saunders Glasklar Editions 3-D and Glasklar Interactive CD-ROM series
|Megasystems' CD-ROMs allow you to explore dozens of virtual-reality images, like this android from Technology 3-D.|
Image courtesy of Megasystems
Ever wonder how the mechanical pressure of your fingers on a computer keyboard translates into electrical impulses that appear as images or text on your screen? Even if you were inclined to rip apart your personal computer to find the answer, you'd probably still end up mystified. But with the new CD-ROM set The World of Technology 3-D,
you can pull up a 3-D graphic of a laptop with a transparent outer case that reveals the inner landscape of circuit boards. Then, using your mouse, you can spin the laptop up, down, left, or right to see the machine from every angle. The World of Technology 3-D
is one of several new CD-ROM sets available for $19.95 apiece from Megasystems (www.megasystems.de
) that turn learning into an adventure in virtual realism. Each set encapsulates a particular world of wonder and is brimming with movies and animation that make dozens of entries snap to life. Animated clips with voice-over narration in The World of Technology 3-D
demonstrate a range of phenomena, from the physics of an ax wedge splitting open a tree trunk to the elegant mechanism of a fountain pen. You can tag along as a Tyrannosaurus rex
tromps through the green forests of North America in Dinosaur 3-D,
or rotate the heavens with a star-navigator feature in Interactive Cosmos
that shows how the orientation of the sky changes with the seasons. You can use a movable X-ray viewer in Interactive Human Body
to explore layer upon layer of tissues, muscles, organs, and bones. And you can watch the drool flow in The World of Animals 3-D
as you replicate the classic conditioning experiment in which Ivan Pavlov trained a hungry dog to salivate at the sound of a bell.
Click on "crustaceans" in The World of Animals 3-D
and you can find a chart of their entire geologic time span, including each burst of crustacean evolution—the emergence of trilobites about 440 million years ago, the dawn of crabs 40 million years ago. A time line in The World of Technology 3-D
marks the date of the first generation of personal computers to come on the market: 1983. Members of the video-game generation who can't remember that far back may find their curiosity for real science sparked by these CD-ROM sets. In an instant they can transform a personal computer into a virtual laboratory, a time machine, or an archaeological dig. Books Terrestrial Seasoning
Pass the salt, please By Eric Sorensen Salt: A World History
By Mark Kurlansky
Walker and Company
In the course of reading Mark Kurlansky's Salt: A World History,
I went through a plate of prosciutto with melon, one small pizza, a quarter pound of sliced corned beef, a Caesar salad thick with anchovies, some beef jerky, lox on a bagel, and enough olives to choke a horse. I got pretty thirsty. But as I satisfied my personal craving for this common seasoning, I also grew delightfully sated by Kurlansky's chronicle of this deceptively simple compound. Salt through the ages has brought about revolution, war, the first state monopoly, and numerous scientific and technological breakthroughs.
Salt is the only rock we eat. Before the advent of refrigeration and canning, it was the most common way of preserving food, absorbing the moisture that bacteria need to grow as well as killing bacteria outright. It ages milk in the form of cheese so deliciously that the French were inspired to create more than 400 varieties of fromage.
More important, salt is essential to survival. The salt we absorb from our diet plays a critical role in the functioning of cells by providing such necessities as the electrolytes that transmit nerve impulses.
"A salt," Kurlansky writes, "is a small but perfect thing."
And it is practically everywhere: There's sodium bicarbonate in our baking soda, magnesium chloride and potassium chloride in our baby formula. The most common salt, of course, is sodium chloride, a dicey union between the unstable metal sodium and the deadly gas chlorine. Generically salt is the simple marriage of any acid with any base, which contributes a spare electron. On such chemistry we have built countless pillars of civilization. Most Italian cities, including Rome, were founded near saltworks. The quest for salt led Chinese engineers in the 11th century to develop drilling techniques that remained unmatched by anyone else for another seven centuries: Sichuan workers drilled hundreds of feet to find brine that they drew off and evaporated for its salt residue.
Salt is so common and so easy to obtain these days that we tend to take it for granted. "We have forgotten that from the beginning of civilization until about 100 years ago, salt was one of the most sought-after commodities in human history," writes Kurlansky. We now pay only a few dimes at the store for a container of free-flowing Morton's, but in the American Civil War, men paid with their lives to defend strategically important saltworks.
Kurlansky, who found equal success with another short title, Cod,
draws on his extensive travels around the world in this volume and on his substantial gift for storytelling. This work offers an unusual mix of science, geology, engineering, and the culinary arts. The result is a smorgasbord of history that pays homage to a long-overlooked but essential ingredient in human affairs. Science Best-sellers
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|* Source: Barnes & Noble Booksellers|
Cautionary Tales from the Limits of Human Endurance
Ballantine Books, $24.
How does it feel to travel to death's doorway? Stark examines what goes on in the minds and bodies of adventurers who put themselves in mortal danger, from mountain climbers who struggle against subfreezing conditions to divers who face the potentially deadly accumulation of nitrogen bubbles in their veins. The Northern Lights:
The True Story of the Man Who Unlocked the Secrets of the Aurora Borealis
Alfred A. Knopf, $24.
The physicist Kristian Birkeland made several globe-girdling expeditions between 1899 and 1919 to witness the majesty of the aurora borealis, or northern lights. Jago weaves an intimate tale of Birkeland's life and studies, which laid the foundation for ongoing research into how interactions between the solar wind and Earth's magnetic field cause the famous light displays. Mysteries of Terra Firma:
The Age and Evolution of the Earth
James Lawrence Powell
The Free Press, $25.
Powell chronicles how scientists during the last century used modern tools, such as radiocarbon dating and ocean submersibles, to solve three of the all-time greatest geologic mysteries: Earth's age, the inferno-driven process of continental drift, and how meteoroid impacts shaped Earth and the planetary neighbors that share our solar system. Earth From Above, 365 Days
Harry N. Abrams, $29.95.
Arthus-Bertrand's stunning aerial photography shows the face of the Earth both in its natural splendor and in relationship to its human inhabitants. The varied altitudes at which his images are shot create a pleasurable visual disorientation that's resolved only when you locate a background object to get a sense of scale. With informative captions accompanying its 365 majestic photos, the book makes a handy desk calendar—though you'll probably want to devour it in one sitting.
— Maia Weinstock