The ground beneath us is alive, very alive. A single gram of soil (about a fifth of a teaspoon) can contain thousands of species of bacteria, and millions of individual cells. It might also be packed with fungi, microscopic worms, and other strange creatures like tardigrades and rotifers.
A new atlas, released Wednesday at the United Nations Environment Assembly in Nairobi, attempts to map this biodiversity around the world.
“When we think about biodiversity, we usually think about plants and animals,” says Alberto Orgiazzi, a soil biologist with the European Commission’s Joint Research Centre and one of the principal authors. “But there’s a huge world of organisms under our feet.” Those organisms play important, but largely unappreciated roles in agriculture and natural ecosystems, Oriazzi says. The goal of the atlas was to drum up a little love and respect for these mostly invisible life forms among policy makers and the general public—and to convince people that they’re worth protecting.
Reading it just might turn you into a soil geek. The book is an encyclopedia as much as it is an atlas, with hundreds of beautiful photographs and photomicrographs of soil-dwelling organisms, like the myriapod above (which belongs to the same taxonomic group as centipedes and millipedes).
It’s also brimming with fascinating tidbits of soil science. You know that earthy smell after a good rain? It comes from a compound called geosmin that’s made by Streptomyces bacteria and released when they die. The human nose is extremely sensitive to it. It’s the same compound that gives beets their earthy flavor.
The deepest known plant roots—223 feet (68 meters)—were discovered in the Kalahari Desert. But that’s nothing compared to nematodes: The tiny roundworms have been found 2.2 miles (3.6 kilometers) below the surface.
The map above is just a first attempt at mapping soil biodiversity, Orgiazzi says. DNA testing is the modern method for studying soil biodiversity, but scientists haven’t had the money or time to test every point on the globe (or anywhere close to that). So, they used statistical models that consider things like the climate and soil type and acidity to estimate biodiversity. In general, Orgiazzi says, the tropical regions richest in plant and animal life are also richest in soil biodiversity.
The researchers also tried to estimate the threats to soil biodiversity around the world, based on the best available data. You can see large swaths of red in the map below, but the reasons vary by region. In India, overgrazing is a major threat, Orgiazzi says.
Our Good Earth: Why Soil Matters Photographs by Jim Richardson, National Geographic Creative
In large parts of Europe, North America, and China the main threat is agriculture, especially the heavy-handed use of fertilizer and pesticides. In sub-Saharan Africa, it’s wind erosion and the threat of reduced rainfall with climate change.
The new atlas contains guidelines for protecting soil biodiversity, from less intensive farming methods to limiting erosion and controlling invasive species. The first step, though, will be getting people to pay more attention to the living world right beneath their feet.
The atlas, published by the Joint Research Centre, contains contributions from more than 120 soil experts. The digital version is freely available to download.