The emergence of the global sulfur cycle approximately 2.8 billion years ago is often associated with the beginning of life on Earth. Oxidation of sulfide-rich minerals, such as pyrites, to form sulfate (SO42−) is an important part of the cycle; organisms assimilate sulfate, which they convert to organic sulfur, an essential component of proteins. In addition to chemical processes on continental shelves and slopes, rivers deliver a substantial amount of sulfate into the oceans. The Kaoping River, at 170 kilometers long, is one of the largest rivers of Taiwan. Compared to its size, the river delivers a disproportionately large amount of water, sediment, and chemicals into the global oceans. In a new study, Das et al. use sulfur isotopic ratios (δ34S) to trace the sources of sulfate in the Kaoping River basin. The researchers found that chemical weathering of pyrites, particularly during the rainy season, contributes more than 85% of the sulfate in this basin.