When men first landed and walked on the moon, one of the myriad fears of NASA scientists was that the spacecraft—or Neil Armstrong—would sink and disappear into the lunar soil. No one was sure what it would comprise, how deep it would be, and whether it would support weight. Luckily for Armstrong, lunar soil isn’t really soil at all; it’s about three feet deep, largely incompressible, and essentially little more than debris that’s been building up for billions of years, as meteor after meteor has struck the moon’s surface and broken up the rock there.

The moon may be pretty to look at from Earth, but its soil is sort of a letdown. Not so the soil of the Earth. Forget for a moment the fact that soil is the core of every food chain we’ve got. Put aside that it is also a storehouse for essential scientific information about everything from climate change and greenhouse gases to long-lost cultures and our own evolution. Soil is also very much alive, in ways researchers are only beginning to explore. In fact, UAB geologist Scott Brande, Ph.D., wouldn’t be surprised if the next great frontier in scientific inquiry takes place at ground level. “We know so little about the living component of the soil and its relationship to life on the planet,” he says, “that we may be looking forward to a century of discovering things we just didn’t know existed, right under our feet.”

Soil is complex, to say the least. “It’s the product of rock that’s been weathered physically and chemically, plus gases from the atmosphere and from decomposition,” begins Brande. “Plus water and moisture, plus the microbial communities and the other organisms living in it. It may be one of the most complex substances scientists study.”

Brande resists restrictive descriptions. “You could say that the average soil is half broken-down mineral matter, and maybe a quarter organic matter. But that’s like describing all American men by saying that they are, on average, five feet, 10 inches tall.” This is because the factors that create soil—rocks, rainfall, heat, cold, plants, animals, and insects—are simply too varied. So granite in Alaska will not break down to become the same type of soil as granite in Mexico. In Hawaii an inch of topsoil may take 1,000 years to form, while in Brazil the topsoil layer can be up to 300 feet thick.

Washing It All Away

Soil is also always in flux, either from the constant processes of weathering or the tampering of man—or both. The good earth that has made the Southeast an agricultural stronghold, for example, can quickly morph into a barren land. “Through weathering, the mineral nutrients from all the variety of rocks get broken down,” says Brande, “and then they’re carried away by groundwater. So over time the soil becomes less and less suitable for agriculture.”

More important, feeding the world is taking its toll. In general, we grow things faster than the natural system would on its own, in order to feed more than six billion people on the planet—a number that will swell to 13 billion in the next 25 years. “We’re going to need more arable land, not less, and so the soil conservation service is trying to promote practices that conserve the soil,” says Brande. “But we’re still seeing growing problems with erosion in many parts of the U.S. and the world.”

Even soils that are the thickest—those in the equatorial zone, where physical conditions best promote the breakdown of bedrock minerals—are easy to leach of nutrients. The ever-fertile rainforest soils of Brazil can be rendered lifeless in just a year or two, says Brande. Although the soil level in the rainforest is deep, the soil immediately below the root system is actually exceedingly nutrient-poor, because what’s released in the process of weathering is washed away by the great amounts of rainfall.

“The clearing and burning of the rainforest “litter”—“those incredible surface communities of trees, shrubs, insects, and animals”—releases an initial pulse of nutrients that is consumed by the first few seasons of crops,” says Brande. “So after that first pulse, in order to sustain the crops, you ironically have to fertilize that once-rich soil tremendously.”

Man’s Dirty Deeds

For a small percentage of Americans, soil isn’t just the medium for growing food; it’s a meal in itself. Arguably, only cultural chance has kept dirt-eating, or geophagia, from becoming more widespread. If your great-grandmother is Swedish, Japanese, Finnish, Javan, Peruvian, Mayan, or West African, she may have once heard of a good recipe for a soup or bread that featured soil as an ingredient. Religious traditions involving the ingesting of dirt span the globe. Slaves brought to the Americas from African nations continued their native practice of eating soils, and the habit was common among women during pregnancy. In some rural communities in this country, the practice still exists.

People who eat dirt are sometimes nutrient-deficient—low levels of calcium or iron, for example, can cause a person to crave chalky substances such as clay. What human bodies can extract from dirt, though, is debatable: Many of the soils that are regularly eaten are dominated by a ferrous-oxide form of iron, which is poorly absorbed by the body. But by and large, many geophages, when asked why they do it, say they simply enjoy the taste.

Geophagia is often classified as the psychiatric disease pica—the ingesting or mouthing of nonnutritive substances, which can range from soils to cigarette butts to soaps and rubber gloves. Gabriel Garcia Marquez’s character Rebecca experienced a geophagic episode as the result of love-crazed madness in One Hundred Years of Solitude: “Rebecca got up in the middle of the night and ate handfuls of earth in the garden with a suicidal drive, weeping with pain and fury, chewing tender earthworms and chipping her teeth on snail shells.”

Those earthworms and snail shells are exactly the reason physicians and nutritionists unilaterally recommend against earth-eating, culturally sanctioned or otherwise. In addition to constipation, dirt can cause intestinal blockages and perforations, potassium intoxication, hypertension—even poisoning, if contaminants have penetrated the soil.

Dirt-eaters don’t generally go for just any old ground. The white clay soil that can be found for sale at roadside stands in the Southeast is largely kaolin, the main calcifying ingredient in Kaopectate. Packages of red clay are rich in iron oxide and aluminum oxide. Brande explains that the two chemical compounds that give red clay its color are actually produced by weathering from the breakdown of other existing minerals. “Those two compounds are fairly stable,” he says, “so they accumulate while lots of the other mineral components created by weathering decompose and wash away.”

The Hidden Life of Grime

Climate is particularly important in determining the character of soil, Brande notes—not just because it determines rainfall and temperature (and therefore weathering of the bedrock), but also because it controls what kinds of plants, animals, and insects can live in that environment. And it’s the living content of the soil that is most underexplored, says Brande. “It’s almost an unseen world.”

“It’s easy to forget about these creatures because of their microscopic size,” agrees UAB microbiologist Asim Bej, Ph.D. “But they’re everywhere.” Much of Bej’s research focuses on what he calls extremophiles—microbes that live in extremely harsh environments once considered lifeless, such as the dry valley soils of Antarctica. “Imagine jumping into a swimming pool of water that is highly acidic or an extreme temperature,” he says. “Certain extremophiles actually thrive in such environments.”

All cells have the same basic underlying structure and properties, so it’s hard to imagine how any living organism can survive the temperature range in the soils of Antarctica without some kind of protection. “That’s the primary goal of my research—to reveal the mechanisms of cold and subzero temperature tolerance in microorganisms that live in the surface and subsurface soil,” says Bej. “In other words, I’m trying to identify what they use as their ‘blankets.’ We want to better understand how they can carry on their cellular activities in such extreme conditions, because these microbes share fundamental characteristics with all plant and animal life.”

His studies also include “toxin eaters,” or microbes that use harmful pollutants as a food source in a process known as bioremediation, which has already been successfully tested by humans as a way to help clean up certain toxic chemical spills. “When we find microorganisms in a contaminated area, it is a sign that they can survive by degrading the pollutants,” says Bej. The more scientists learn about how extremophiles thrive in conditions that normally damage other organisms, the more widely bioremediation strategies can be applied to pollution problems. “And if we can use the indigenous population of microorganisms to clean up the environment,” Bej says, “we can do so without disturbing the delicate balance of life in that area.”

Extreme soils aside, Brande is quick to point out that we are all intimately bound to the Earth’s unique and wide range of habitable ground. “Without this incredible life-producing material,” he says, “our planet would largely be dead.”