Farmers harvest sesame in Syria. PHOTO: JIM RICHARDSON

The 68th UN General Assembly declared 2015 the International Year of Soils. It aims to increase awareness and understanding of the importance of soil for food security and essential ecosystem functions. According to scientists, soil is being eroded faster than that the Earth can replace it. So the next time the words ‘dirt cheap’ come up, think again and take not the soil below your feet for granted.

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. Furthermore, dirt is proactive. It’s not an inert blanket; it’s a dynamic entity.

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 Pimenteland 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.

National Geographic’s The Plate brings you more here.