Synopsis of The Secret Life of Dust
Dust is everywhere, both on planet Earth and throughout the cosmos.
Usually regarded as an annoyance at cleaning time, this humble substance actually plays an important role in everything from the formation of stars to the falling of rain. A new book by noted science writer Hannah Holmes proves that the subject of dust is anything but dry.
In The Secret Life of Dust, Holmes tells us that the substance—which comes in a bewildering array of shapes, sizes and compositions—may also be responsible for the extinction of several species, including the dinosaurs and, perhaps in time, our own. Holmes’ fascinating and deeply researched account assembles the views of a number of scientists who devoted their careers to studying this omnipresent substance. Dust coalesced billions of years ago to form the first stars, which in turn manufactured heavier atoms such as carbon, the basic building block of terrestrial life. When stars explode, they shatter into huge glowing clouds of gas and dust that become nurseries for new stars. Dark clouds of interstellar dust, though, can block earthbound telescopes and obscure these and other celestial marvels.
A good deal of dust is man-made. As Holmes reveals, people don’t just create it through agriculture and industry. Like Pigpen in the Peanuts comic strip, each of us walks the earth in a cloud of dust, shedding fragments of skin and bits of lint torn from our clothes through friction. With all that dust around, Holmes’ look at the hazards it can pose is rather unsettling. A more immediate threat than some far-off nuclear winter, dust of various kinds kills people every day all over the world. Lung diseases such as silicosis affect desert dwellers who inhale tiny sand particles; people contract cancer from secondhand smoke; and babies play on floors that are the inevitable destination of gravity-bound lead and chemical dusts.
A welcome addition to The Secret Life of Dust is an appendix of Web sites that illustrate Holmes’ intriguing revelations about the topic. A gifted writer, Holmes turns a seemingly unremarkable substance into the stuff of a great story.
—Gregory Harris
Excerpt from The Secret Life of Dust
Picture a juice glass sitting on a porch railing in the sunshine. It may look empty, but churning inside that glass are twenty-five thousand microscopic pieces of dust - at least. And these dusts are a little bit of everything on Earth. One minute, they are tiny crumbs chipped off Saharan sand, and invisible shreds of camel hair. Then the wind shifts, and there are spores of forest fungi and fragments of desiccated violets. A bus stops nearby to take on passengers, and invisible flakes of human skin, mixed with miniscule specks of black soot momentarily dominate the mix. Every time you inhale, thousands upon thousands of motes swirl into your body. Some lodge in the maze of you nose. Some stick to your throat. Others find sanctuary deep in your lungs. By the time you have read this far, you may have inhaled one-hundred-fifty thousand of these worldly specks - if you live in one of the cleanest corners of the planet. If you live in a more grubby region, you've probably just inhaled more than a million. Although these dusts have been waved aside for most of human history, in this book we'll see that dust is terrifically consequential. Some dusts menace the planet and its living residents. Some are beneficial to people, plants, and animals. Many are merely fascinating. All are going under the microscope. And the secret lives of dust are being revealed.
One of the most impressive revelations is how much of it surrounds us - the sheer tonnage of stuff rising off the face of the Earth. Because dust is so small and shifty, the estimates are still rough. Nonetheless, irrefutably huge amounts of small things take to the wind each year.
Between one and three billion tons of desert dust fly up into the sky every year. One billion tons would fill fourteen million box-cars, in a train that would wrap six times around 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 the wind, perhaps one-third of which condenses into tiny, sailing beads. Plankton, volcanoes, and swamps leak twenty to thirty million tons of sulfur compounds, about half of which forms little airborne specks. Burning trees and grasses throw up six million tons of black soot. The world's glaciers slowly grind their host mountains into dust that takes to the wind - but 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, fibers of rotting leaves, eyes of flies and legs of spiders, scales from the wings of butterflies, hair fragments from polar bears, skin flakes from elephants - how many tons of these roam the atmosphere? About four million years ago, our ancestors began to augment the dusty exhalations of Nature.
At first, we supplemented the soot, as we mastered the mesmerizing tool of fire. Then, when we learned about the miracle of metals, our smokes grew richer with microscopic beads of hot bronze, iron, copper, gold, and silver. The advent of spinning and weaving created invisible fragments of 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 a hundred million tons of sulfur now rise annually from the world's fossil-fuel burners - mainly, coal-fired power plants, but also oil-fired plants, and diesel engines. Every natural sulfur bead in the sky is now accompanied by between three and five human-made beads. And the Earth hosts more fuel-burners every day.
More than a hundred-million tons of nitrogen oxides, which like sulfur gas is prone to form dusty particles in the sky, flow upward from our farms, automobiles and other fuel-burning inventions. Eight million tons of black soot in the sky is attributable not to burning trees and grasses, but to the conflagration of fossil fuels - especially coal. Even of the six million tons of soot that rain upward from fires, most are lofted by the fires of humanity.
Whether the skies carry one billion or three billion tons of desert dust, fully half may be our responsibility. Our agriculture and other assaults on the landscape may have doubled the amount of desert dust naturally present in the air.
And the miscellaneous dusts of the twentieth century - nerve-wracking mercury and stupefying lead, carcinogens from dioxin to PCBs, the radioactive dusts of nuclear disasters, pesticides, asbestos and poisonous smokes - how many tons of these roam the skies each year? That is undetermined.
If the quantities of dust are hard to gauge, dust scholars have an easier time pinning a size on various dusts. Generally, the dusts that whirl around us are so small that gravity has to fight to get control of them. Forces on the surface of a piece of dust - static electricity, even the interaction of one atom with another - can overpower the call of gravity. Dust can perch on the ceiling as easily as on the tabletop.
Scientists measure dust in microns, a twenty-five thousandth of an inch. Consider the hair on your arm. A single hair might be one-hundred microns wide. Now imagine taking up scissors, and snipping off a section one-hundred microns long. That tiny 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 a hair. These fat dusts are usually the work of Nature. The diameter of pollen grains, for instance, ranges from a full hair's width to one-tenth of a hair's width. If you sift a handful of sand from the beach or the desert, the faint powder that sticks 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 to form an invisible halo around you, are rectangles one-tenth of a hair wide, and two-tenths of a hair long. Many of the salt flecks that blow off the oceans are upward of five microns wide. And those are still some of the larger dusts. Health scientists fret more about small dusts than large ones. That's because the 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 inside the nose - as people with allergies are well aware. But small dusts can slide right past the traps inside your head, and sail deep into your delicate lungs.
Until recently, scientists drew the line between safe and dangerous dusts at ten microns - one-tenth of a hair's width. But as dust investigators peered more closely at their little subjects, they decided to move the line. Medical research now shows that dusts less than one-quarter that big - one twenty-fifth of a hair - cause the most disease and death. Even as they rewrite dust limits to protect 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 make the cut: Bacteria and fungal spores are usually well under ten microns. But industrial dusts are the dominant force in the "teensy" category. Pesticide dusts are between half a micron and ten microns wide. The very biggest particles in a puff of tobacco smoke are less than a half-micron wide - that's one two-hundredth of a hair. The smallest particles in automobile exhaust are a one-hundredth of a micron - one ten-thousandth of a hair. This is also the realm of tiny particles that form when gases condense into beads in the air. Viruses and big molecules are about the same size. You can begin to imagine how twenty-five thousand of these tiny motes could roam a juice glass unnoticed.
For all the murder and mischief we'll see dust commit in this book, dust is nonetheless indispensable. The Sun we circle was created inside a giant womb of protective space-dust. Some of that same dust, tiny specks the size of cigarette smoke, came together to make our planet. In cosmically large quantities, dust blackens the Milky Way, blocking our view of most of the stars. And each star that dies rains more dust out into the galaxy, like a black firecracker. It is this dust of expired stars that forms the next generation of Suns, Earth, and bodies.
