Figure 1.

(a) Sampling a carbonate-brucite chimney from the Lost City that is venting fluid at approximately 95°C and pH (at 25°C) 10.8. (b) The exteriors of these chimneys are coated with biofilms that can be observed along the edges and in the cracks of the chimneys. Most of these biofilms inhabit conditions much more moderate than in the focused flow shown in part A. (c) Scanning electron microscope image of a Lost City chimney demonstrating the close interactions among carbonate (lower left and centre of image), brucite (triangular platy material) and biofilms. Image credits for (a) and (b) S. Q. Lang, U. of S.C./NSF/ROV Jason/2018 © WHOI. Image credit for (c) T.R.R. Bontognali, Space Exploration Inst./S.Q. Lang, U. of S.C./G.L. Früh-Green, ETH-Zürich/SNSF. (Online version in colour.)