Photograph by Jim Richardson, National Geographic
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Farmers harvest sesame in Syria.
Photograph by Jim Richardson, National Geographic

Common as Dirt, Which Isn’t Actually all That Common

This year is the International Year of Soils. This may not sound as catchy as previous international years, variously devoted to such topics as Water Cooperation, Sustainable Energy, Forests, Biodiversity, and Rapprochement of Cultures–but the truth is that the United Nations could hardly have made a better pick. Given that we can’t survive without it, it’s amazing how few of us truly appreciate dirt.

Look at the way we talk about it: Dirty thoughts are reprehensible. Dirty linen is embarrassing. Dirty tricks are mean. If something is deemed low and worthless, it’s said to be common as dirt; and to treat someone like dirt means indulging in some truly despicable behavior. Dirt, in other words, is a shockingly under-respected commodity, given that six inches of dirt are all that lie between us and extinction. No dirt and we’re dead as doornails.

Furthermore, for all that, there seems to be dirt all over the place, there actually isn’t all that much of it. A common demonstration of this involves an apple.

Cut the apple in quarters and set three aside. These represent the portion of the globe occupied by the world’s oceans. Slice the remaining quarter in half. One half represents land that’s essentially uninhabitable: people-unfriendly regions like Antarctica, the Sahara Desert, and the peaks of the Himalayas. Divide the other half—people territory, a mere one-eighth of the globe—into four pieces. Set three of these aside: these represent land unsuitable for growing food, being too cold, too wet, too rocky, or inaccessible to farmers and gardeners, having been slathered over with houses, highways, apartment buildings, shopping malls, skyscrapers, and parking lots. The final intimidatingly skinny slice—just one-thirty-second of the Earth’s surface area—is all that we’ve got for dirt. That’s it: arable land, the minuscule sliver of the planet that all 7.3 billion of us depend upon for food.

Dirt is not only rare, but it’s complicated. To the uninitiated, dirt may look like grubby generic mush, but actually it has character, individuality, and a taxonomy all its own. Soil scientists recognize twelve major orders of dirt, each divided into suborders, groups, subgroups, families, and series, according to its various allotments of minerals and organic matter. Each dirt has a pedigree. The dirt in our backyard, for example—the stuff in which we plant tomatoes and hammer horseshoe pegs—is a spodosol, of the Suborder Orthods, Great Group Haplorthods, Typic Subgroup, Tunbridge Soil Series.

Furthermore, dirt is proactive. It’s not an inert blanket; it’s a dynamic entity. We know this, because we’ve seen what happens when it malfunctions, as in the sobering story of Biosphere 2. Biosphere 2, a high-tech crystal palace erected in the Arizona desert, was designed to reproduce in miniature the Earth’s biosphere (the big one, Biosphere 1).

In the early 1990s, Biosphere 2 was home to eight people and 3,000 species of plants, animals, fish, and insects, variously scattered over seven mini-biomes, among them a pint-sized tropical rainforest, savannah, marsh, and even an ocean, simulated by a million-gallon saltwater aquarium. The concrete foundations underlying the Biosphere were covered with dirt, 30,000 tons of it, mixed to 30 different recipes. The theory was that all the Biosphere’s tiny ecosystems with their resident populations of flora and fauna would interact and equilibrate, eventually creating a stable and self-perpetuating Eden. It was hoped that Biosphere 2 would serve as a model for future space colonies.

Instead, Biosphere 2 went to pot. Beneath its glittery glass roof, carbon dioxide levels shot up, and oxygen levels dipped dangerously down. Most of the animals and insects abruptly went extinct, except for the indestructible cockroaches and one particularly tough and annoying breed of ant. Crops failed; and eventually the project, suffering from environmental meltdown, reached the point of no return.

Subsequent analyses showed that the prime culprits in this eco-fiasco were soil bacteria run amok, multiplying at unprecedented rates. Biosphere 2 ultimately crashed because its soil recipes were wrong. The Biospherians were done in by dirt.

Dirt, scientists guess, has been around for about 450 million years. Unlike our endlessly recycling water, however, dirt doesn’t stick around forever. Dirt is ephemeral. Wind and water steadily strip it away. It’s scraped off the Earth’s surface by glaciers, washed into the oceans by thunderstorms, blown into the atmosphere by wind—as happened in drought-ridden Oklahoma, Texas, and Kansas in the 1930s, the years of the Dust Bowl. The Earth, of course, continues to produce dirt, but it takes its time about it. Estimates vary, but most agree that it takes anywhere from 100 to 500 years to produce an inch of topsoil.

Which is why we’re now in trouble. Worldwide, according to David Pimentel and colleagues at Cornell University, soil is being eroded faster than that the Earth can replace it. The United States is losing soil ten times faster, and India and China 40 times faster, than the natural replenishment rate. Pimentel calculates that global cropland, from which we get 99.7 percent of our food, is shrinking at a rate of 37,000 square miles a year. According to the Natural Resources Conservation Service (NRCS), about one-third of the world’s arable land has been lost since 1950, a victim of deforestation, desertification, over-plowing, and overgrazing.

And the soil that we’ve got left isn’t in great shape, largely due to poor farming methods that strip away valuable carbon, rendering it less and less productive. According to sustainable agriculturist John Crawford, at our current rate of soil degradation, we’ve got just 60 years’ worth of viable topsoil left. And that’s just not going to be enough to feed the 9 billion people we’re expecting by 2050, which is why dirt is a big focus for National Geographic this week as we look to World Food Day on Friday.

As awe-inspiring items go—compared to the Grand Canyon, say, or Stonehenge or the Hope Diamond—dirt is low on the admiration totem pole. I’d say it’s time for an image makeover. Photographer Jim Richardson’s dirt gallery, Our Good Earth, is a good place to start.

Diamonds may be forever, but we’re not. We’re only here because of dirt.