Since 1779 photosynthesis has been the standard-issue explanation for the continuation of life on earth: plants absorb sunlight, which fuels their metabolism, and create oxygen as waste. This is such basic, grade-school science that it normally wouldn’t bear mentioning, but in July 2024 a team led by Andrew Sweetman at the Scottish Association for Marine Science reported a startling finding in Nature. On the deep seafloor—where light never penetrates—oxygen is apparently being produced by rocks. These rocks are known as polymetallic nodules, which form over the course of millions of years when small debris like sharks’ teeth attract trace metals from the surrounding seawater. The seafloor is covered in a viscous ooze, composed of the compressed skeletons of dead marine life, and the nodules lie strewn atop it, packed closely together. Sweetman and his team were investigating the microbial life in this deep-sea environment by lowering custom-designed chambers into the depths, creating a seal around seafloor sediment. Generally, the oxygen within the chambers decreases as various organisms consume it. In the nodule fields, against all …