THE WORLD IN A GRAIN OF DUST
Picture a juice glass sitting on a porch railing in the sunshine. It may lookempty, but churning inside that glass are twenty-five thousand microscopicpieces of dustat least. And these dusts are a little bit of everything on Earth.One minute they're tiny crumbs chipped off Saharan sand and invisible shredsof camel hair. Then the wind shifts, and you are surrounded by spores of forestfungi and fragments of desiccated violets. A bus stops nearby to take on passengers,and flakes of human skin mixed with minuscule specks of black sootmomentarily dominate.
Every time you inhale, thousands upon thousands of motes swirl into yourbody. Some lodge in the maze of your nose. Some stick to your throat. Othersfind sanctuary deep in your lungs. By the time you have read this far, you mayhave inhaled 150,000 of these worldly specksif you live in one of the cleanestcorners of the planet. If you live in a grubbier region, you've probably just inhaledmore than a million.
Although these dusts have been waved aside for most of human history, inthis book we'll see that dust is terrifically consequential. Some dusts menacethe planet and its living residents. Some are beneficial to people, plants, andanimals. Many are merely fascinating. All are going under the microscope. Andthe secret lives of dust are being revealed.
One of the most impressive revelations is how much dust surrounds usthesheer tonnage of stuff rising off the face of the Earth. Because these specks areso small and shifty, the estimates are still rough. Nonetheless, irrefutably hugeamounts of small things take to the wind each year.
Between 1 and 3 billion tons of desert dust fly up into the sky annually. Onebillion tons would fill 14 million boxcars, in a train that would wrap six timesaround the Earth's equator.
Three and a half billion tons of salt flecks rise off the oceans.
Trees and other plants exhale a billion tons of organic chemicals into thewind, perhaps one-third of which condenses into tiny, sailing beads.
Plankton, volcanoes, and swamps leak 20 to 30 million tons of sulfur compounds,about half of which forms little airborne specks.
Burning trees and grasses throw up 6 million tons of black soot.
The world's glaciers slowly grind their host mountains into dust that takesto the windbut in what quantities? No one knows.
Likewise, how many glassy bits of volcanic ash are blasted into the ether?
And the dusts of life-flying fungi, viruses, diatoms, bacteria, pollen, fibersof rotting leaves, eyes of flies and legs of spiders, scales from the wings of butterflies,hair fragments from polar bears, skin flakes from elephantshowmany tons of these roam the atmosphere?
About 4 million years ago our ancestors began to augment the dusty exhalationsof nature. At first we supplemented the soot, as we mastered the mesmerizingtool of fire. Then, when we learned about the miracle of metals, oursmokes grew richer with microscopic beads of hot bronze, iron, copper, gold,and silver. The advent of spinning and weaving produced invisible fragmentsof animal and plant fibers, which the wind lifted out of our encampments. Finally,with the industrial revolution, our dust output shifted into high gear.
Ninety to 100 million tons of sulfur now rise annually from the world'sfossil-fuel burnersmainly coal-fired power plants, but also oil-fired plantsand diesel engines. Every natural sulfur bead in the sky is now accompanied bybetween three and five human-made beads. And the Earth hosts more fuelburners every day.
More than 100 million tons of nitrogen oxides, which like sulfur gas areprone to form dusty particles in the sky, flow upward from our farms, and automobilesand other fuel-burning inventions.
Eight million tons of black soot in the sky are attributable not to burningtrees and grasses but to the conflagration of fossil fuelsespecially coal. Evenof the 6 million tons of soot that rain upward from tree-and-grass fires, mostcan be traced to the human hand.
Whether the skies carry 1 billion or 3 billion tons of desert dust, fully halfmay be our responsibility. Our agriculture and other assaults on the landscapemay have doubled the amount of desert dust naturally present in the air.
And the miscellaneous dusts of the twentieth century-nerve-rackingmercury and stupefying lead; carcinogens from dioxin to polychlorinatedbiphenyls (PCBs); the radioactive dusts of nuclear disasters, pesticides, asbestos,and poisonous smokeshow many tons of these roam the skies eachyear? That is unknown.
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If the quantities of dust are hard to gauge, dust scholars have an easier timepinning a size on various dusts. Generally, the dusts that whirl around us are sosmall that gravity has to fight to get control of them. Forces on the surface of apiece of duststatic electricity, even the interaction of one atom with anothercanoverpower the call of gravity. Dust can perch on the ceiling as easilyas on the tabletop.
Scientists measure dust in microns, or twenty-five-thousandths of an inch.Consider the hair on your arm. A single hair might be 100 microns wide. Nowimagine taking up scissors and snipping off a section 100 microns long. Thattiny snippet, visible only if you know where to look for it, is too big to be dust.From a scientist's perspective, that snippet falls in the family of sand.
The very biggest grains of dust are, technically, only two-thirds as wide as ahair. These fat dusts are usually the work of nature. The diameter of pollengrains, for instance, ranges from a full hair's width to a tenth of a hair's width.If you sift a handful of sand from the beach or the desert, the faint powder thatsticks to your palm will be a range of sizes, with lots of grains in the fatter category.The flakes of dead skin that float out through the weave of your shirt toform an invisible halo around you are rectangles one-tenth of a hair wide andtwo-tenths of a hair long. Many of the salt flecks that blow off the oceans areupward of 5 microns wide. And those are still some of the larger dusts.
Health scientists fret more about small dusts than large ones. That's becausethe human body has evolved to bar the entrance of nature's big creations.Nearly all pollens, for example, are so big that they get hung up insidethe noseas people with allergies are well aware. But small dusts can slideright past the traps inside your head and sail deep into your delicate lungs.
Until recently, scientists drew the line between safe and dangerous dusts atten micronsone-tenth of a hair's width. But as dust investigators peeredmore closely at their little subjects, they decided to move the line. Medical researchnow shows that dusts less than one-quarter that biga twenty-fifth of ahaircause the most disease and death. Even as scientists rewrite dust limits toprotect our lungs, they're still struggling to understand how tiny dusts kill.
So which dusts fall on the small side of the line? A few natural dusts makethe cut: bacteria and fungal spores are usually well under 10 micronsBut industrial dusts are the dominant force in the "teensy" category. Pesticidedusts are often between half a micron and 10 microns wide. The very biggestparticles in a puff of tobacco smoke are less than half a micron widethat',one two-hundredth of a hair. The smallest particles in automobile exhaustare a hundredth of a micron-one ten-thousandth of a hair. This is alsothe realm of tiny particles that form when pollution gases condense intobeads in the air. Viruses and big molecules are about the same size. You canbegin to imagine how 25,000 of these tiny motes could roam a juice glass unnoticed.
For all the murder and mischief we'll see it commit in this book, dust isnonetheless indispensable. The Sun we circle was created inside a giant wombof protective space dust. Some of that same dusttiny specks the size of cigarettesmokecame together to make our planet. In cosmically large quantities,dust blackens the Milky Way, blocking our view of most of the stars. And eachstar that dies rains more dust out into the galaxy, like a black firecracker. It isthis dust of expired stars that will form the next generation of Suns, Earths,and other heavenly bodies.
And here on Earth we wouldn't want to do without dust. For starters, a cleanworld would be an oppressively muggy world. In the planet's water cycle, waterevaporates off the oceans and lakes, condenses in the air, and falls back to theground. But that condensation step assumes a sky full of dust, upon whose littlesurfaces water vapor can gather. Without dust, water vapor wouldn't beginto condense until the relative humidity was about 300 percent. This would makethe sultriest summer day seem dry and crisp by comparison. For lack of a moresuitable nucleus, the water vapor would condense on your body.
Since a cloud is just a collection of water droplets condensed around variousdusts, a shortage of dust also implies a shortage of clouds in the sky. Andclouds reflect much of the sunlight that hits them, casting shade on theplanet. At any given time, they cover about half the Earth. Without them, itwould get mighty warm down here.
Many of the dusts that roam the Earth are little bits of life, whose ability totravel on the wind keeps the planet healthy and green. Fungi, for instance,make a living breaking down a variety of substances, including the dead fleshof plants and animals, and even rocks. Their efforts free trapped nutrients andenrich the soil. And the overwhelming majority of fungus species haveadapted to fling their spores into the wind. These tough spores travel theworld, falling back to Earth at the whim of wind and rain.
Many pollens also evolved to exploit the wind. The bigger grains hitchhikeaboard bees and other nectar hunters. But the smaller ones sail through the airon their own, perchance to touch down on a suitable flower, thus ensuring theperpetuation of green and growing things.
Microscopic diatoms, which are glass-shelled algae, may distribute themselvesthis way, too. Even minuscule worms called nematodes are smallenough to climb onto the wind and spread their race. Antarctica, for instance,was probably scrubbed clean of life in the last ice age. But now a variety of microorganisms,including the relatively large nematodes, have colonized thecold patches of dirt in the continent's McMurdo Dry Valleys. The most likelyexplanation for their presence is that their ancestors flew in from South America,Africa, or Australia.
Among the many marvelous subtopics of dust research, one that refuses todry up and blow away is the notion that some tiny life forms not only ride thewind, but also reproduce in that dusty domain. Various researchers have proposedthat some bacteria help water vapor to condense in the sky and then divideand multiply inside the drops they create.
Even the billions of tons of lifeless rock dust that clot the air downwind ofdeserts are valuable to the Earth. Certain islands in the Caribbean would benaked, gray rock if it weren't for the dusts of deserts and volcanoes that settleheavily upon them. Instead they are humps of lush and happy vegetation.Likewise the tapestry of the Amazon rain forest is indebted to dust. In such arainy climate, water quickly flushes nutrients out of the soil. But each winter,when the trade winds head southwest from the Sahara, rich dust rains downon the South American forests and refreshes the soil.
Falling rock dust feeds tiny mouths in some of the world's most desolateplaces. On the Earth's glaciers, settling dust arrives like a catering service,spreading assorted dishes out for the enjoyment of some of the hardiest lifeforms we know of. Even inside a glacier we'll see that well-traveled dust can sustaina tiny web of life. Dust that falls in the ocean can also fuel a bloom ofplants. These plants are microscopic phytoplankton. But despite their unobtrusivesize, plankton are the bread and butter of the oceanic food chain. Andin a twist on the "dust to dust" cycle, they sometimes take nutrients fromfalling desert dust and then send aloft a sulfur-rich dust that plays a key role informing clouds.
To some degree, scientists have learned how an assortment of living anddead dusts tinker with the weather. And it's now becoming clear that dust altersthe world's long-term climate, too. Traditionally, climatologists have focusedtheir fears on gases that trap heat near the Earth, but as the globe getswarmer, little airborne specks have become a very big topic. Scientists nowknow that some of our dusts reflect sunlight and cool the planet. And others,especially our black soots, may be soaking up huge amounts of heat as theyroam the sky. Some marvelous theories even implicate a global blizzard of dustin the sudden retreat of the glaciers at the end of the last ice age. But for now,the brightest minds on Earth can't say exactly what dust is doing to the thermostat,whether for better or worse.
The relationship between dust and humanity has also been complexforthousands of years.
Eight thousand years ago, Chinese farmers discovered the charms of massivedeposits of desert dust that had settled out of the air in central China. Thisblanket, about three hundred feet thick, was effortlessly tilled and nutritiousfor plants. Today similar dust deposits all over the world, including the centralUnited States, are under intense cultivation. Unfortunately, as we'll see, looseningthis ancient dust can sometimes be disastrous.
Perhaps four thousand years after Chinese farmers dug into their dust, peoplein ancient Mesopotamia were melting down their own local powder tomanufacture rocks. At a site called Mashkan-shapir, archaeologists recentlydiscovered large, flat rectangles of black rock, whose composition resembledno natural basalt. But the chemistry of the rocks did match the dust depositedon the banks of the local river. The archaeologists speculated that a naturalshortage of wood and stone inspired the people of Mashkan-shapir to heattheir dust to twenty-two hundred degrees, then mold the molten dust intorocks.
At that same early date, the people of Finland were exploring the merits of aspecial dust of their own. This dust, which was pounded from strange, fibrousrocks, strengthened the clay that they used for both pottery and house chinking.Farther south in Europe, people eventually learned to weave the fibers ofthis same rockasbestosinto fireproof cloth. And early naturalists did noticethat asbestos weavers were a particularly unhealthy lot.
On the other side of the world the Maya people at Tikal, Guatemala, seemto have carefully added a substantial percentage of volcanic dust, or ash, totheir pottery to toughen it. That tradition demands a large supply of ashwhichhas produced a mystery: The nearest ash deposits aren't terribly closeby. Was volcanic dust so valuable that it was worth lugging through a hundredmiles of jungle? An alternative explanation is equally intriguing: CentralAmerican volcanoes were a lot more active a lot more recently than we realize,throwing their ash all the way to Tikal.
Today humanity still employs dust for planting crops, for building, and forPotteryand for thousands of other purposes. Cement walls are a mixture ofrock dust and pebbles. Sheetrock is a mineral powder, compressed into a convenientform. Colored dust gives paint its hue. Rock dusts give scouring powderits grit, toothpaste its polish, and talcum powder its silkiness. Eye shadowcan be a mixture of dazzling dusts, from talc to powdered fish scales and pigments.Aspirins and vitamins are compacted dusts. Magazine paper is madeshiny with the thinnest coating of dried clay dust. Pencils hold a core ofpressed graphite powder. Bread is made of powdered wheat kernels, and so ispasta. Yellow mustard is the dust of mustard seeds, and soft cocoa is the dustof hard cocoa beans. Modern life relies heavily on dust.
One reason we powder so many things is that dust offers huge amounts ofsurface area to work with. Since chemical reactions generally take place on thesurface of an object, the more surface you can provide, the more intense the reactionwill be. Imagine, if you will, steeping fifty whole coffee beans in a mug ofhot water. Yuck. Then imagine grinding fifty coffee beans to dust and repeatingthe experiment. Or imagine dropping a bar of solid soap into the washingmachine with a load of clothes. Then imagine shredding that soap into powderand repeating the exercise. More surface area permits more interaction.
This characteristic can produce results both wonderousand woeful.
Some of the dusts that swirl around us are fearsome and invisible rogues.Leave aside for a moment poison particles launched by human industry. Plainold desert dust has a dark side of its own.
Seventy-five million years ago, for instance, simple desert dust seems tohave set a subtle trap for a fieldful of dinosaurs. One minute these formidablecreatures were going about their domestic duties. And the next minute thedust in the surrounding sand dunes conspired to entomb them. (The detectivework required to reconstruct such an old murder scene, and to implicatesomething as easily overlooked as dust, is considerable, we'll see.)
Perhaps those dinosaurs were the lucky ones. Ten million years later the dinosaurstory would come to a much slower and more final close, as a worldwidecloud of dust from a giant meteorite impact darkened the sky and blottedout the Sun. That dust murdered birds, sea life, and small, pioneering mammalspecies as well.
Desert dust still delivers trouble to this day. A dust-related disease standscharged with the slaying of purple sea-fan corals. Dust from the Sahara haslong beaten a path across the Atlantic Ocean to rain down on the Caribbean.But in the 1970s a terrible drought in the African Sahel region south of thegreat desert began to send extra dust rolling down this skyway. And as thefalling dust grew thick in the Caribbean in the early 1980s, scientists saw aplague sweep through the coral reefs. Coincident with the dust invasion, twospecies of coral were nearly wiped out, a species of sea urchin was decimated,and the purple sea fans developed dark, lumpy lesions. It took some sleuthing,but a scientist has pinned the sea-fan plague on a fungus in the Saharan dust.
Scientists are now examining this dust more closely and finding everythingfrom radioactive elements to mercury and an impressive array of fungi. In thesummer in southern Florida, says one longtime dust scholar, this far-flungdesert dust is the most common sort of particle in the air. There may be implicationsfor human health.
Health experts already know that some dusts can be deadly to people. Whenthey rank U.S. cities by the quantity of pollution dust in the air, then rank thesame cities by deadliness, they find a match. The dustier the city, the higher thedeath rate. One federal agency estimates that pollution dusts alone kill sixtythousand people each year in the United States. The crucial question in thiscase of mass murder is ... which dusts do the killing?
Some dusts are obviously fatal. Coal dust, for instance, kills 1,500 minersevery year in the United States. The dust of powdered quartz kills 250 moreminers, sandblasters, and other laborers in this country. The needle-shapeddusts of asbestos cause deadly cancers of the lung and gut. But none of thosedusts hangs terribly thickly in city air. Something else is at work. The clues arepiling up against the tiny chemical dusts of our own making.
The dusts we find indoors can be as kind and as cruel as those foundoutside.
The dust bunnies that skulk beneath the couch and behind the refrigeratorcontain everything from space diamonds to Saharan dust to the bones of dinosaursand bits of modern tire rubber. But they also hold poisonous lead andlong-banned pesticides, dangerous molds and bacteria, cancer-causing smokeparticles, and a sample of all the convenient chemicals that we innocently distributethrough our houses in the name of cleanliness. The dust bunny is riddledwith allergy-inducing dust-mite parts, with the mites themselves, andwith the predatory mites and pseudoscorpions that stalk and kill them.
In addition, house dust bears some blame for lead poisoning among children.As children crawl across carpetingespecially aged, dust-packed carpetingtheirsticky little paws gather dust. And then those paws go into theirmouths. One of the best indicators of how much lead a child's blood will containis how much lead a sample of carpet dust contains.
Oddly, if it weren't for the chemicals and metals that foul house dust, wemight learn to love our dust bunnies. For decades, allergists have shot up someof their patients with a distillation of dust taken straight from the vacuum-cleanerbag. Although the secret to the success of this bizarre protocol isn'tknown, allergists swear it does tame dust allergies. And some of the most rivetingresearch in all of dust science is now drawing a connection between dustyhomes and healthy children. An epidemic of asthma is exploding among thechildren of developed nations. But a flurry of studies is showing that babieswho do their crawling and finger sucking in dusty, germy houses are less likelyto get the wheezing disease. Something in house dust, doctors insist, musttoughen a baby's immune system.
Indoors or outdoors, dust is unavoidable. And a marvelous fraction of thatdust holds the secret to our past.
Some of the dust that swirls around us was knocked off distant, collidingasteroids eons ago. Some of it boiled off comets that may have passed our waya few years ago or a few centuries ago. This stuff, still holding its ancient grainsof primordial stardust, settles on Earth at a rate of one magical speck persquare meter per day.
Because these extraordinary dusts carry the secret of our cosmic past, we'llsee that scientists go to extreme measures to capture them. And catching thesemicroscopic time capsules is only half the battle: To analyze such smoke-smallspecks is sometimes simply impossible. But whenever a dust scholar is abletease out the chemical fingerprint of a grain of space dust, she comes a little bitcloser to understanding the origins of our world.
That is the secret of our past.
Excerpted from THE SECRET LIFE OF DUST by Hannah Holmes. Copyright © 2001 by Hannah Holmes. Excerpted by permission. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.