Tuesday, November 20, 2012

Dust

A series on the Dustbowl Days is running on PBS now, and to be sure the afflicted people endured great hardships in the 1930s. But it bears remarking that, in a more stealthy way, dust covers us at all times if we let the outside air in at any time. Left alone, given time, it would eventually cover everything. Today, doing chores in the basement, a toilet paper roll escaped me and ran under the stairs. I retrieved it using a broom handle through its welcoming center cavity—and that alerted me to masses of dust where I sweep rather rarely. Today was such an occasion. Once daily also, in that same basement, I wipe my computer screen. It accumulates a uniformly-spaced population of dust particles.

Dust particles are incredibly small. One source† puts atmospheric dust as small as 0.001 µm; that symbol stands for micrometer, meaning one millionth of a meter, in this case a thousandth of a millionth of a meter. They carry electric charge and hence are very sociable, so that my broom this morning carried a veritable halo of grey fluff while also moving the larger dust particles on the ground, ranging up to a gigantic 10 µm. I also noted, in looking things up, that dust carries a message: All things are connected. Wikipedia assures me that my gathering this morning probably contained a few meteorite particles along with just about anything you can name, organic and inorganic. They’ve come a long ways to decorate, almost invisibly, the darkest shadows beneath the stairs, sharing space there with a gigantic cardboard box that, aging, probably contributes its own tiny bits originating in the forests of our southern states where corrugated boxes take on life.

The image I show is actually a dust particle from the Moon, obtained from NASA indirectly via Journal of Young Investigators (link). The particle is too small for the human eye to see. Here it is enlarged using an electron microscope. And lo and behold. The particle is cratered, like the Moon itself. According to NASA, the craters were made by super-tiny meteorite particles crashing on the Moon and then carving homes for themselves on the dust particle itself. With such attacks constantly bombing us, how can we ever hope to win?
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†Lide, David R. “Characteristics of Particles and Particle Dispersoids.” Handbook of Chemistry and Physics, 75th Edition. Florida: CRC Press, 1994.

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