Fig. 1.

Hydrothermal vents and WLP. There are two distinct types of hydrothermal vents. So-called “black smokers” (A) are acidic and driven by heat from underlying magma. Alkaline vents (B) are produced by a chemical reaction called serpentinization, when sea water reacts with certain minerals in olivine. Fresh-water hydrothermal fields (C) are generally acidic due to dissolved sulfur oxides and are analogous to the WLP analyzed by the Pearce et al. (1). Images courtesy of (A) Office of Ocean and Atmospheric Research/National Undersea Research Program/National Oceanic and Atmospheric Administration; and (B) Wikipedia Commons/National Science Foundation (University of Washington/Woods Hole Oceanographic Institution).