Despite its importance, we know little about the soil—and human activities could put it at risk. That’s why soil scientists in the college are exploring its mysteries and developing new ways to repair damage, detoxify pollutants, increase crop production by managing soil microbes, and more.

Soil is much more complicated than any other part of our ecosystem. For one thing, it contains most of the planet’s biodiversity. A teaspoonful of topsoil contains more than 1 billion bacteria, and these bacteria may belong to as many as 10,000 species.

“The surface soil also holds, on a global scale, more than twice the amount of carbon than that of all the earth’s vegetation and atmosphere combined,” says environmental soil chemist Jon Chorover. “That means any soil disruption could have a huge effect on climate change.”

Environmental soil chemist Jon Chorover (standing) uses the Hawaiian Islands as a natural laboratory to assess how soils of different ages hold on to carbon. His work may shed light on the impact soils have on global warming.

Scientists are beginning to include the soil in models used to predict global warming. When tropical forests are burned and converted to farms, huge increases in greenhouse gases follow. This “exhalation” seems to be related to disturbances in the soil structure. “As soils develop, particles gather into clusters that surround and protect organic matter from decomposition,” Chorover explains. “But when those clusters are broken by tillage or deforestation, microorganisms can get to the organic matter, degrade it, and readily release it to the atmosphere as carbon dioxide.”

Chorover wants to learn more about how soils hold onto carbon. To do this, he travels to a place where soils are born.

The Hawaiian Islands are a great place to study how soils develop—seriously! This archipelago of more than 20 islands is continuously growing as the earth’s crust moves over volcanoes on the ocean floor. Fresh lava bubbles to the surface, hardens into basalt, then goes through the weathering process that creates new soils.

Each Hawaiian island is made of the same parent material, basalt; each has within it a location with the same humid, tropical climate, receiving the same average rainfall over the year and supporting the same forest vegetation. “This eliminates much of the variation we usually have to deal with in field studies,” Chorover says. “The primary difference between sites that we are working on is their age.” By sampling across the islands, Chorover can compare fresh rock to very ancient soil ecosystems, making it an impressive natural lab.

Whether they’re in the South Pacific or central Pennsylvania, soils develop in a fairly predictable sequence. First, the parent material is broken into particles by physical processes like rain and wind. These large particles then begin to chemically weather, transforming into secondary minerals and nutrient cations.

“There’s a progression to smaller and smaller particles until you end up with this biogeochemically reactive medium,” Chorover says. “There are all these surfaces that microbes can attach to and take advantage of organic materials floating by—that’s why microbial diversity in soils is so incredibly high. It’s this same complexity that makes soils uniquely capable of storing huge amounts of organic carbon.”

Each year, a layer of plant litter falls to the forest floor. The litter goes through humification—the process by which soil fungi, animals, and bacteria transform the litter into humus, carbon dioxide, and soluble organic compounds.

Rainwater percolates through the decaying litter, picking up thousands of different organic molecules—like water flowing through a tea bag. The water, brown now, continues leaching downward until it reaches the mineral layers.

There, something curious happens.

“When we sample from more than a meter in depth, the water’s clear again,” Chorover says. “The organic compounds have been selectively adsorbed by the mineral surfaces. And once those compounds are locked on mineral surfaces, microorganisms can’t feed on them as easily.”

It’s this interaction between minerals and organic matter that’s crucial to understanding how soils hang on to organic carbon. In Hawaii, Chorover hopes to learn if the humification process differs in older versus younger soils. If it does, scientists may be able to assess how a soil’s age could affect its potential impact on global warming.