 Soil erosion is a global threat. Each year 75 billion tons of fertile soil is lost from world agricultural systems. Nuclear testing in the 1950s and the 60s released radionuclides, such as cesium-137 into the atmosphere, in extremely low but measurable quantities. Over time, through precipitation, cesium fallout was deposited worldwide on the soil's surface. Because it bound strongly to fine soil particles, it became possible to use the presence of the cesium as a tracer, which provided science with a way to measure soil erosion. In the 1970s, scientists clarified the relationship between cesium and soil erosion, and from the 80s and 90s until now, they have refined this nuclear technique, creating a method to gather reliable and comprehensive data on the magnitude and rate of soil erosion. What is this cesium-137 method? How does it work? The cesium-137 method uses gamma spectrometry measurements to compare the total cesium-137 content in eroding or depositing sites with the cesium-137 content at undisturbed, stable areas known as reference sites. If the cesium-137 content is lower than the reference site value, it means that soil has been lost to erosion. While if the content is higher than the reference site level, it indicates that soil has been deposited there. This information provided by the cesium-137 method identifies areas with high erosion and sediment transfer, and enables better targeting of soil conservation measures, increasing our ability to control and mitigate soil losses caused by erosion and to reduce its environmental impact.