Lost City Hydrothermal Field
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Lost City is a field of alkaline hydrothermal vents in the mid-Atlantic ocean that differ significantly from the black smoker vents found in the late 1970s. The vents were discovered in December 2000 during a National Science Foundation expedition to the mid-Atlantic. A second expedition mounted in 2003 used DSV Alvin to explore the vents. The details of the chemistry and biology of the Lost City hydrothermal field were published in March 2005.
A similar alkaline hydrothermal vent, the Strytan Hydrothermal Field, has been identified off the north coast of Iceland.
The vents are located on the seafloor mountain Atlantis Massif, where reactions between seawater and upper mantle peridotite produce methane- and hydrogen-rich fluids that are highly alkaline (pH 9 to 11), with temperatures ranging from <40° to 90°C. There is a field of about 30 chimneys made of calcium carbonate 30 to 60 meters tall, with a number of smaller chimneys.
Lost City vents release methane and hydrogen into the surrounding water; they do not produce significant amounts of carbon dioxide, hydrogen sulfide or metals, which are the major outputs of volcanic black smoker vents. The temperature and pH of water surrounding the two types of vent is also significantly different. Strontium, carbon, and oxygen isotope data and radiocarbon ages document at least 30,000 years of hydrothermal activity driven by serpentinization reactions at Lost City, making the Lost City older than known black smoker vents by at least two orders of magnitude. Correspondingly, Lost City and black smoker vents support vastly different lifeforms.
The Lost City supports a variety of small invertebrates associated with the carbonate structures, including snails, bivalves, polychaetes, amphipods, and ostracods. Large animals, however, such as tube worms and giant clams that are abundant in typical black smoker vents are absent at Lost City. A variety of microorganisms live in, on, and around the vents. Methanosarcinales-like archaea form thick biofilms inside the vents where they subsist on hydrogen and methane; bacteria related to the Firmicutes also live inside the vents. External to the vents archaea, including the newly described ANME-1 and bacteria including proteobacteria oxidise methane and sulfur as their primary source of energy.
Speculation has been offered that ancient versions of similar hydrothermal vents in the seas of a young Earth are the birthplace of all life, constituting the original abiogenesis. The free hydrogen, metallic catalysts consistent with an iron-sulfur world theory, micro-cellular physical structure of the towers and available hydrothermal energy might plausibly have provided an environment for the beginnings of non-photosynthetic energy cycles common to archaea and organic molecule creation. These alkaline hydrothermal vents also continuously generate acetyl thioesters, providing both the starting point for more complex organic molecules and the energy needed to produce them. Microscopic structures in such alkaline vents "show interconnected compartments that provide an ideal hatchery for the origin of life".
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