How Dirt Breaks Down in Carpets

Origins

• All dirt began as bits of rock, broken from the bedrock of the planet by earthquakes or thrown up by volcanoes as the planet cooled. Rocks and gravel broke into sand with the help of primitive lichens and the action of water. As life forms developed, old plants and animals died, providing distinctive combinations of carbon-rich organic matter to the mix. Minerals such as iron and copper provided color in areas where they were plentiful. Eventually, layers of subsoil -- gravelly rock on the way to becoming soil -- and organic-rich topsoil covered the base rock over the entire earth.

What’s Tracked In

• All carpet consists of woven fibers full of tiny openings, all the perfect size for dirt and dust particles. The dirt that ends up on the carpet is the result of soil picked up on shoes -- or mud if it’s wet -- and airborne dust, pollen and dander, some of which carries oils from skin. Dirt particles might even serve as homes to microscopic insects such as dust mites that “jump ship” as the dirt hits the carpet, taking off to find a new home, often in the carpet itself. Whole dirt particles can be pulled out of the upper levels if carpets are vacuumed weekly and stains are immediately treated.

Upper Levels

• Products of biological decay and the bacteria that facilitate decay cling to woven carpet fibers that strip components away from dirt as it falls through the carpet’s pile. The loosest bits of oxidized minerals and lightest organics from the dirt stick in the upper, most visible levels of the carpet. Dander flakes and less dense, newly added organic waste may also catch on fibers. The densest organic components travel farther down into carpet’s pile as foot traffic shifts the fibers around.

Lower Levels

• Every particle of dirt has a different history and contents. Each, however, sheds lighter, irregularly shaped organic elements in the upper parts of the pile. Insects and bacteria might migrate to lower levels as the fabric continues to scrape organic components off of the dirt particle as gravity pulls it down. Grains of sand are the last and heaviest component to land. The sand nucleus falls through the pile into the backing, or base of the carpet, and lodges in the woven jute or polypropylene, finally coming to rest atop foam padding or the underlying floor. Sand might be pulled up by extraction cleaners, but it will not dissolve and end up in the bottom of the vacuum tank with bits of minerals.