Wolfe - Tales from the underground: a natural history of subterranean life

Man and mans earth are unexhausted
and undiscovered.
Wake and listen!
Verily, the earth shall yet be a source of recovery.

FRIEDRICH NIETZCHE (1911)
AND THUS SPAKE ZARATHUSTRA

O NE DOESNT HAVE TO VENTURE FAR INTO THE UNDERGROUND for new discoveries. Step out into the backyard, for example, push your thumb and index finger into the root zone of a patch of grass, and bring up a pinch of earth. You will likely be holding close to one billion individual living organisms, perhaps ten thousand distinct species of microbes, most of them not yet named, cataloged, or understood. Interwoven with the thousands of wispy root hairs of the grass would be coils of microscopic, gossamer-like threads of fungal hyphae, the total length of which would best be measured in miles, not inches. Thats in just a pinch of earth. In a handful of typical healthy soil there are more creatures than there are humans on the entire planet, and hundreds of miles of fungal threads.

Some zealous soil ecologists have recruited small armies of graduate students and marched them into forests and grasslands to compile a complete inventory of subterranean life. Within a dimension of one square yard (about one square meter), they typically uncover billions of microscopic roundworms called nematodes, anywhere from a dozen to several hundred of the much larger earthworms, and 100,000 to 500,000 insects and other arthropods (species with hard exoskeletons). And thats in addition to the astronomical numbers of fungi, single-celled bacteria and protozoa, and other creatures that dont fall into these major groups. Many of the arthropods are very tiny and can be spotted only with a magnifying lens. Some defy classification; they simply have never been seen before. Even in well-studied areas, new arthropods and other multicellular species of unknown function are routinely encountered.

The numbers are staggering, the biodiversity fascinating, and the potential for discovery unsurpassed by any other habitat on Earth. Yet we have spent more time and effort examining small patches on the surface of the moon and Mars than exploring the subterranean habitat of our own planet. The words of Leonardo da Vinci ring as true today as they did five hundred years ago: We know more about the movement of celestial bodies than about the soil underfoot. Even in modern laboratories, scientists are lucky if they can come up with the right nutrient mix to culture and study 1 percent of the microbes found in a typical soil sample. This poor success rate is due in part to the complex interdependence between subterranean organisms. They cant survive when isolated from their neighbors. Until very recently, we knew next to nothing about the 99 percent of soil microbes that we could not raise in captivity except what their rotting cellular remains looked like under a microscope.

NEW TOOLS, HOWEVER, have opened a window to the underground, ushering in a cornucopia of subterranean discovery. Many of these tools have been borrowed from the tool chests of molecular biologists. The same molecular techniques that allow modern crime labs to detect a fragment of the genetic material left by a suspect at a crime scene allow modern soil labs to probe for evidence of specific organisms or characterize the full range of microbial diversity in a pinch of soil or a rock sample from the deep Earth. This still leaves many questions unanswered, such as the function of the many genetic types found. However, by identifying similarities in the genetic codes of newly discovered organisms and those we are already familiar with, scientists are often able to determine the ecological role played by previously unknown genetic types. At this point, the scientific community is grateful simply to have an opportunity to begin to quantify and catalog all that we have been missing.