Lost City sits on Atlantis Massif at Mid-Atlantic Ridge intersection. Field spans 500 square meters at 750-900m depth. Hosts 30 active and inactive carbonate chimneys up to 60m tall. Serpentinization of ultramafic peridotite generates H2 and CH4. Vents emit alkaline fluids at 40-90°C with pH over 9. Older than black smokers by two orders of magnitude. Supports Methanosarcinales archaea thriving on H2 and CH4 biofilms. Bacteria oxidize methane and sulfur externally. Lacks tube worms and giant clams of black smokers. Hosts snails, bivalves, polychaetes, amphipods on carbonates. Microbes are polyextremophiles: alkaliphiles, piezophiles, thermophiles. Site speculated as abiogenesis hatchery via H2, catalysts, compartments. Similar to Prony Bay vents producing H2 and CH4. Possible on Europa and Enceladus with olivine and water. Discovered 2000 via Alvin submersible. Multiple expeditions drilled cores and sampled fluids. Faults orient vents east-west. Mass wasting scars slopes around field. Chimneys evolve from white brucite-aragonite to grey calcite.