This is a tale of transformation. It is a story of death and rebirth, of rot giving way to redemption, and of miracles hiding in plain sight.
Like all such stories, it begins humbly, in lowly refuse: coffee grounds and apple cores, things we throw away without a second thought. Most of us live in urban settings, and the words refuse, dirt, and soil conjure up overflowing trash cans, foul with half-eaten hamburgers, soiled napkins, things only a rat could love.
But besides being “soiled,” there is another sense of the word, as in “the soil of the homeland.” Here the soil is something to be proud of, something hard-won and precious. This is the soil of the farmer's field, rich and dark and moist as a chocolate torte. This is the soil which thaws after winter to release the heady fragrance of spring, at once honeyed and earthy: the smell of growing grass and returning warmth.
Anyone who has planted a seed, infinitesimal as a grain of salt, and months later pulled from the ground a full-blown carrot or beet knows that soil is capable of strange and wonderful magic. Soil must be a sort of powdered life-force, pregnant with undifferentiated potential.
In Barcelona, Spain, is a beautiful open market known as La Boqueria, dating from 1217 C.E. and offering a dizzying variety of fruits and vegetables every day: eggplant, artichoke, and arugula; pithaya, pomegranate, mangosteen. La Boqueria is a carnival of Earth's fecund whimsy, of the multifarious forms the soil brings forth. With W.B. Yeats, pondering on the sources of his own inspiration, we might wonder about the origin of those fruits:
We know that our garbage is buried in the earth, and that from the earth grow orchards and crops, but what happens in between?
Take a handful of soil, and look more closely. Like a cake made of non-cake elements – flour, eggs, sugar – the soil comprises a bit of everything else on Earth: mineral particles, water, air, organic matter. But the list “flour, eggs, sugar” fails even to approximate a recipe for cake, let alone convey the vast assortment of Black Forest, Lady Baltimore, and Pineapple Upside-Down cakes which might result from combining the basic elements.
Soil ranges from peat, a dense airless pudding of decayed bog plants, to desert sand, light and dry as sifted flour. Tiny grains of rock weathered from the Earth's crust form its mineral base, varying in chemistry and in particle size. Put that handful of soil in a glass of water, and over a few days it will separate into layers like a parfait, the organic matter floating near the top while minerals settle into layers of decreasing particle size: sand at the bottom, topped by silt and clay. The widths of these bands yield composition by percentage, classifying soil texture on a triangle nuanced as a painter's color wheel.
If soil texture is a complex affair, the inclusion of organic matter – castoffs from the plant and animal kingdom, in various states of decay – explodes the classification to more than 17,000 distinct recognized soil types in the U.S. alone. Chemistry, climate, and formation broadly divide these soils into twelve orders, their occurrence mapped symbolically in color over the surface of the globe.
Soil is no more static over time than it is constant across space. Ascending another level in complexity above the organic matter, we find our handful of soil inhabited by a teeming bureaucracy. Bacteria and fungi form the proletariat, a billion tireless first responders breaking down leaves as they fall. Dependent on them for nourishment are the middle management: mites by the hundred, along with thousands of protozoans and those simple microscopic tubes known as nematode worms. Centipedes, beetles, and spiders people the food web's upper echelons. Though equivalent in size to these larger predators, the earthworms, sowbugs, and millipedes are gentle giants feeding on dead plant matter and leaving behind shredded scraps which the microbes easily digest.
As an commonplace byproduct of its everyday existence, this vast hierarchy unlocks stores of nitrogen hoarded in the bodies of deceased plants and animals, releasing the nutrient as soil nitrates which when assimilated will fiber new plants and flesh new animals in turn. Symbiotic bacteria in the roots of certain plants also harvest Earth's plentiful atmospheric nitrogen, rendering it usable for their hosts. Completing a final lobe in the web, denitrifying bacteria replenish atmospheric nitrogen with some of the soil nitrates originally produced by the decay of plant and animal life.
Though we began by examining a handful of soil through the lens of a microscope, we cannot fully comprehend without widening our focus to include the air which touches the soil, the plants it roots, and the animals whose footsteps it supports. Mammalian blood cannot be understood by counting red blood cells on a microscope slide, but by considering the bloodstream and its central role in metabolism. Similarly, soil is not merely the inventory of its chemical resources or the census-count of its citizens, but part of the nitrogen cycle, as well as the carbon cycle and other biogeochemical loops.
Looking at the Earth though not a microscope but a far-away “imaginary telescope” first brought the nitrogen cycle to the attention of James Lovelock, a British scientist who once spent his spare time searching for wild orchids on the Wiltshire downs. Lovelock and his collaborators were hired by NASA in 1961 to devise instruments the Viking lander would use for detecting the presence or absence of life on Mars's surface. In considering this problem, Lovelock first conducted a thought experiment, asking himself whether the known presence of life on Earth could be deduced solely from hypothetical astronomical observations by a telescope in space.
Lovelock's answer was in the affirmative. The Mariner spacecraft had already analyzed Venus and Mars's atmospheric compositions from space, and even earth-based telescopes were able to glean information on these planets' atmospheres through infrared observations. Analogous experiments would reveal the make-up of Earth's atmosphere to a telescope in space or on Mars, and the imaginary astronomer manning this observatory could construct a table comparing the atmospheres of Earth, Mars, and Venus.
Such a table shows Venus and Mars to have remarkably similar atmospheres, almost solely made of carbon dioxide and in a state near chemical equilibrium with their planetary soils. If Mars or Venus were heated and then cooled again, allowing chemicals to recombine according to their equilibrium preferences, they would resume more or less their current configurations. Earth, however, is in a state far from chemical equilibrium, with nitrogen dominating its atmosphere, followed by oxygen and a tiny amount of carbon dioxide. Something or someone must be hard at work twenty-four hours a day to preserve this anomalous state.
Though effectively convincing Lovelock that the Viking lander's search for Martian life was misguided, this thought experiment led him to the Gaia hypothesis: the proposal that the entire Earth is a living organism which maintains itself in homeostasis, a stable condition favorable for life and different from the equilibrium which inanimate chemicals would choose if left to themselves. Human body temperature is an example of homeostasis: whether the air is 0 or 100 degrees Fahrenheit, a healthy human has a constant body temperature of 98.6, maintained through regulatory feedback mechanisms such as shivering to keep warm or sweating to cool off.
Viewed from the Gaian perspective, the nitrogen cycle is indeed part of a living being's metabolism. Every nitrifying or denitrifying soil microorganism is part of the feedback loop maintaining a favorable distribution of Earth's nitrogen for the flourishing of life. We have laid our hands on the soil and felt the warm pulse of a sleeping giant.
Unsurprisingly for an idea so bold, the Gaia hypothesis has its share of passionate critics, in large part because it challenges the definition of what it means to be alive. If one includes in this definition, as evolutionary biologist Richard Dawkins does, the possession of a "selfish gene" and the ability to reproduce, the Earth taken as a whole clearly does not meet the criteria. There is, however, no completely successful standard definition of life. As Lovelock whimsically suggests, our innate ability to recognize living beings, paired with our lack of success at advancing a definitive characterization, suggests that the question "What is life?" has an answer classified as top secret and filed inaccessibly in the black box of our unconscious minds.
An alternative to Dawkins's view characterizes living systems not in terms of reproduction but self-production (autopoiesis). First described by the Chilean biologists Humberto Maturana and Francisco Varela, autopoiesis is the process of constant self-motivated update and regeneration through which a cell, for example, renews itself and maintains the conditions necessary for its continued survival. According to this definition, the biogeochemical cycling of nitrogen, carbon, oxygen, sulfur, and water qualify Earth as a living system.
The autopoietic self-motivated quality of the nitrogen cycle is the seat of its greatest power. It sustains the miracle Walt Whitman celebrates in his poem "This Compost," a reflection on the fact that all living bodies must eventually return to the soil:
"It distills such exquisite winds out of such infused fetor,
It renews with such unwitting looks its prodigal, annual, sumptuous crops,
It gives such divine materials to men, and accepts such leavings
from them at last."
What of the "infused fetor" which we leave weekly in trash bags on the curb for the garbage trucks to collect? What is its eventual fate? Will it, too, be redeemed by the agency of nitrogen and carbon cycles?
A typical bag of nonrecyclable trash in the U.S. might be more than 50% composed of biodegradable materials such as kitchen scraps and yard waste, from the EPA's trash composition estimate. In a year, the average household generates 200 pounds of kitchen waste alone. If left to the ministration of earthworms and microbes, this trash could, like leaves fallen to the forest floor, be regenerated and recovered as valuable humus.
Most trash, however, ends in an airtight landfill, insulated from contact with soil by a layer of clay. Slowly and surely its organic content will decompose, but lacking contact with the atmosphere, anaerobic bacteria must effect its demise. Their byproduct is not nitrogen but methane, one of the most powerful greenhouse gases contributing to global warming. Increased methane levels set up a feedback loop of their own, but not a regulatory negative feedback loop such as that keeping human body temperature constant. Instead, methane initiates a runaway positive feedback loop, leading to increased temperature which in turn triggers the release of more methane from normally sequestered ocean deposits.
Knowing the power of biogeochemical cycles, it seems sheer lunacy to refuse the soil's promised redemption of any cast-off from the biosphere. There are, fortunately, alternatives to landfills: many cities are beginning to introduce industrial composting programs, in which residents sort the organic matter from their trash for separate collection. Given the cost of running and maintaining landfills, not to mention constructing new ones when old landfills reach capacity, a composting program could benefit every city, in economic returns as well as free soil fertilizer.
In regions where no municipal composting program exists, anyone with a little outdoor space, even a small patio having a garden plot or planting containers, can compost independently. The only requirement for success is a good ratio of green materials (wet, nitrogen-containing) to brown (dry, carbon-containing). With proper ventilation and hence aerobic decomposition, there will be no smell except that sweet earthy fragrance lent to healthy soil by the presence of actinobacteria.
Humans too live on Earth, and affect the operation of biogeochemical cycles. Since these cycles are feedback loops regulating the condition of the planet, our actions change the natural homeostasis. By sequestering our trash in landfills, we effectively break the nitrogen cycle, making a sink into which resources fall and cannot be recovered. Ironically, the artificial fertilizers added to farm fields to compensate this loss have produced a surfeit of nitrates in groundwater.
On the other hand, with a bit of thought and minimal effort, we can still reconnect the links we have broken in the web of life. By acknowledging and using the waste management programs inherent in the very soil, we can rejoin the cycling of resources which are the sinew and bloodstream of our planet Earth. | Printer-friendly version | Email this post |
Please share your comments! I welcome thoughts, questions, further information, and civil debate.
 ^ R.C. Lindholm, "Information derived from soil maps: Areal distribution of bedrock landslide distribution and slope steepness," Environmental Geology, Volume 23, Number 4, June 1994, and references therein
 ^ Elizabeth Svoboda, Global Warming Feedback Loop Caused by Methane, Scientists Say, August 29, 2006, National Geographic News.
 ^ Maunsell Australia Pty Ltd, Consultancy Report: Alternatives to Landfill - Cost Structures and Related Issues, September 2003.
 ^ Ecological Society of America, Human Alteration of the Global Nitrogen Cycle: Causes and Consequences, Issues in Ecology, Number 1, Spring 1997.