In one of the few such studies, scientists examined how dead leaves, roots, and other plant litter decay over a decade. The team used stable isotope labels to trace plant litter-derived carbon and nitrogen as the litter decomposed and formed soil, specifically the fraction of soil called organic matter, which comes from plant inputs and microscopic animals. They found that the litter type (needles or roots) and the placement in the soil environment both affected decomposition, but at different timescales.