What is as small as a speck and can fly across an ocean, create rain, or wipe out dinosaurs? The answer is right in front of your nose. It's also under your bed, and in outer space. In fact, dust is almost everywhere.
Dust may seem to be nothing but a housecleaning nuisance, but without it, life on planet Earth would be much different. Actually, there might not be a planet Earth without it. Many astronomers believe the planets were formed from huge clouds of cosmic dust and gas that gravity pulled together.
Today, dust continues to creep into every corner of the planet. Dust forms when water, wind, and friction break off tiny particles of rock and dirt formations. Other sources of dust include ash - blown into the air by volcanoes - pollen, dead skin, and pollutant particles suspended in the air. These are all called aerosols.
Much of the dust in your home comes from small bits of clothing and carpeting that rub off when you move. Dirt tracked or blown inside also adds to your dusting chore. While dust is defined as particles small enough to be carried through the air (less than 1/10th the width of a human hair), these particles settle and collect with hair and other debris to form dust bunnies under your bed.
Outside, aerosols travel much farther. Dr. Joseph Prospero, a professor of atmospheric chemistry at the University of Miami, has been studying dust for over 30 years. During the summertime, a fine red-brown dust fills the air over Florida and other states along the East Coast. By studying this dust and examining satellite images, Dr. Prospero and other scientists have determined that it comes all the way from Africa. Dust storms from North Africa rise up to 20,000 feet high, and trade winds carry the dust across the Atlantic Ocean to the United States, he explains. And this dust is so thick that at times Florida cannot meet government air-quality standards.
Dust: food for rivers and seas
This travel ability of dust has both good and bad effects. Dust, explains Dr. Prospero, creates soil and puts it in some surprising places. Bermuda consists of more than 300 islands off the eastern coast of North America. These islands formed from coral formations created by millions of tiny sea creatures. But the soils that cover the islands were also blown over from Africa.
In South America, dust carries nutrients such as phosphates to replenish the soil along the Amazon River. Dust even helps to fertilize the oceans, by carrying iron into the water to nourish the phytoplankton, the food base for all the ocean's creatures.
Dust that settles on the ocean floor becomes sediment and is pressed deeper and deeper by the pressure of the water. Eventually, it may reach a layer of magma, melted rock inside the earth. Then, during a volcanic eruption, it is blown back into the air as ash or flows across the earth as lava, to be worn down into dust again.
'Earth to dust, come in dust'
Some dust even comes from space. Dust from asteroids and comets is pulled into our atmosphere by gravity. Since 1981, NASA has used high-flying airplanes with special sticky collectors to capture this interplanetary dust for study before it mixes with too much earth dust.
But all dust is not useful. As farmers in the central US first pulled up trees and destroyed grasses to create their farms, they wiped out the plants that held the soil in place. In the 1930s, droughts dried out the soil and wind created huge dust storms that carried the soil away. The dust was thick enough to darken the sky for days at a time. During intense storms, a cubic mile of air could contain over 150,000 tons of dust. Farmers have since learned to plant trees and ground cover to keep their farms from blowing away again.
Some scientists believe dust wiped out the dinosaurs. It is possible that an asteroid crashed into the earth, raising huge clouds of dust that blocked out the sunlight. Plants, which need sunlight, died, and the dinosaurs didn't have enough food. While this is still a theory, scientists agree that large clouds of dust can affect the climate.
Keeping it clean
In manufacturing plants, dust raised by equipment needs to be removed to make the atmosphere breathable for the workers. Shops that paint cars have to remove the dust so it doesn't ruin the paint jobs.
Computer chip manufacturers are even fussier. Dust conducts electricity, so even tiny particles could short-circuit a computer chip. Here, workers must wear special gowns, head coverings, and masks, to keep the dust under control. Cleanliness is also important in laboratories where small particles are studied. It wouldn't look good to discover pollen on a moon rock and then realize it came from a dandelion stuck to your shoe.
For most of us, there's no escaping dust. It fills the air around us, collects raindrops up in our sky, and drifts between our planets in outer space. The next time you wipe the dust off your TV or computer screen, you might think about where that dust has been. This might be a quick stop on its journey around the world or even across the galaxy.
Web sites for dust bunnies
www.usd.edu/anth/epa/dust.html Pictures and information about the Dust Bowl of the 1930s.
daac.gsfc.nasa.gov/CAMPAIGN_DOCS/OCDST/asian_dust.html Satellite photos of a dust storm transporting Asian dust across the Pacific Ocean.
wrgis.wr.usgs.gov/MojaveEco/dustweb/dusthome.html Information and photos showing dust storms in Nevada and California.
www.asci.org/amsci/issues/Sciobs97/sciobs97-09galaxy.html Description and photo of a galaxy with an especially interesting distribution of cosmic dust.
(c) Copyright 1999. The Christian Science Publishing Society