As readers of this blog know, I find the naturally occurring poisons a fascinating subject. Without any help from us, remember, our planet is home to an astonishing variety of dangerous substances - arsenic and antimony, cadmium, lead, mercury, and more. We amplify our exposure to these materials by putting them into industrial products, from cadmium in batteries to lead in paint.
But they originate in the ground beneath our feet - and it's by tracing their path through the Earth's crust that we realize this also means that we need to pay attention to where they are concentrated. It's this point, naturally occurring exposure, that's the focus of a piece I wrote for *The New York Times *today, titled "Landscapes Tainted By Asbestos."
It was dismaying to me to realize the extent of naturally occurring asbestos in the United States. But fascinating to trace the patterns of where it occurs. The map I've posted above is not in the Times piece so I wanted to put it here because I think it eloquently illustrates the way geochemistry shapes our surroundings.
If you look at the map, you'll see that asbestos-bearing minerals are spattered across the country but concentrated in the far west and in solid march through the eastern seaboard. As you've probably realized, its path through the east roughly follows the mountainous stretch of the Appalachia. Fiber-rich minerals, like asbestos, are formed, geologists say, when magnesium and silica deposits are mixed with water and then super-heated by magma rising up from the mantle below.
Most of those eastern deposits were created by the shift and heave of an old crustal boundary some one billion years ago, part of the restless activity that eventually created the mountains we see today. In the west, the asbestos deposits track the faulting created by crustal activity and the closely related history of volcanoes, new and old, in the region. In Nevada, for instance, geologists find fibers associated with jagged landscape formed by plutons, which are huge rock formations caused by liquid magma forced upward into the cooler crust and then solidifying.
And as we understand that, as we map out our sometimes poisonous geology, let's hope that it helps us make good decisions about where we build, what we excavate, and in cases where it's simply unavoidable, how we best protect ourselves.
There's nothing like a good map for making us smarter.
Image: Courtesy of U.S. Geological Survey and Dr. Bradley Van Gosen
