Science: Nearly half of the planet's surface is covered by ocean regions in which life is scarce. These thinly populated ecosystems do not lack water or sunshine, nor the bulk biological elements hydrogen, carbon, and oxygen. Instead, they are deficient in one or more of the other elements necessary for life. Hence, the distribution of life on Earth is captive, in part, to the distribution of the 20 or so bioessential nutrient elements--many relatively rare--that are critical components of DNA, RNA, enzymes, and other biomolecules. Having substantially unraveled this relationship in today's oceans, biogeochemists are beginning to examine how it evolved over the ~4-billion-year history of life on Earth.