Scientists and philosophers occasionally contemplate the tiny tolerances that make life on earth possible. Sometimes they refer to our globe's orbit as the "Goldilocks Zone." If our humble sphere flew just a little closer to the sun, or just a little farther away, water in a liquid state would be impossible and so would, probably, life.
Furthermore, our globe is surrounded by an extremely thin atmosphere, also essential to life. Its thickness depends on the definition of the term "atmosphere," but the layer that we can actually live in is fewer than five miles deep, only .06 percent of the earth's 8,000 mile diameter.
That's a paint-thin film in an unimaginably vast universe.
But if we're not sufficiently awed, as yet, let's cut the margin of life a little closer: let's talk about dirt, the essential ingredient of the thin layer of topsoil that's just about the only place we can grow the things we eat.
I'm an English teacher, not a farmer, so most of what I know about dirt comes from other sources. Few do a better job of describing the state of our dirt than "Dirt: The Erosion of Civilizations," by David R. Montgomery, a professor of earth and space sciences at the University of Washington. I recommend it.
Montgomery points out that our globe is mostly rock, but over very long periods of time rock naturally breaks down into dirt. When it mixes with organic matter it turns into the topsoil of varying depths and quality all over the globe that makes life possible.
Even though it's made of rock, soil is fragile. It tends to flow downhill toward the sea, even when it's protected by ground cover and forest. It blows away easily. Erosion is a very slow process, however, and although the creation of new dirt takes millennia, the natural world manages to achieve a rough equilibrium between creation and depletion.
Cultivation undermines this equilibrium and increases soil's fragility. Plowed fields erode much more quickly, and under the worst conditions-drought, storms, bad tilling practices-farms have been known to blow away down to the bedrock.
Soil wears out, as well. In fact, the story of civilization is largely informed by soil depletion. Historically, whenever new land was readily available, farmers found it easier and cheaper to leave exhausted fields behind rather than use agricultural techniques that preserve the growing capacity of the land.
At present, our dirt is still extremely productive, but farmers have to depend heavily on pesticides and fossil fuel-based fertilizers. However, they're bumping up against limits that weren't imagined by the pioneers who surveyed the millions of acres of fertile land that stretched out toward the west.
In a sense, our dirt has become a semi-sterile medium that supports seeds while they're nourished by artificial fertilizers derived from oil.
This approach to agriculture isn't sustainable, and farmers are responding. The entire February issue of the classic agricultural journal The Progressive Farmer is devoted to "soil health." It chronicles the stories of farmers who are increasingly turning to techniques that not only preserve the soil but enhance its productivity.
Techniques such as the use of cover crops, no-till cultivation and crop rotation have measurable positive impacts on soil quality. Some farmers are developing an ingenious synergy among the manure of grazing cattle, nitrogen-fixing cover crops and the worms and beneficial microbes that inhabit every square foot of soil. You can learn more about this "underground movement," as The Progressive Farmer calls it, by checking out the Soil Health Institute online.
These techniques aren't ground-breaking; farmers have known how to care for their dirt for centuries. But the value of the soil-health initiative is two-fold: It argues that farmers who use soil-enhancing techniques can compete in economic terms with industrial-scale, monoculture agriculture.
And this movement is coming at a good time, when the pressures of climate change and an expanding population are reminding us just how much our lives depend on the two to ten inches of topsoil that lie precariously in favored places around the globe.