Nature: Two proponents of the theory that life originated at deep-sea thermal vents have published a paper explaining how cellular ion pumps could have evolved. In present-day cells, the energy released by the flow of ions across the cell membrane is used to create the cells’ principal source of fuel, ATP. The ion transfer is mediated by proteins, whose production by cells is fueled by ATP. A paradox therefore arises: Which came first, ion pumps or cells? Nick Lane of University College London and Bill Martin of the University of Düsseldorf in Germany argue that an ion gradient could be produced by the combination of alkaline and acidic water in the iron- and sulfur-rich rocks of thermal vents. Small pores in the rocks would serve as the cell membrane, allowing for the passing of ions but trapping larger atoms and molecules. That would concentrate any simple organic molecules that formed and enable the creation of complex proteins and RNA molecules. Over time, an organic membrane, which mimicked the ion gradient of the rock, could have formed as well, and when it fully surrounded the proteins and RNA, it could have formed the first true cells.