tower stands approximately tall on the north side of Posidon, though the chimney has stalagmite-like growths that are as tall as . IMAX has a large flange which catches hot, escaping fluid and has a very apparent biofilm acting within it. Other chimneys, such as Ryan and Nature to the east of Posidon, also have flange and beehive-like structures, though they are significantly smaller and vent significantly less than Posidon. Several inactive vents are located about south of Posidon, though they only stand a few meters tall. Since the location of the massif is upon a slow to ultra-slow spreading center, there is a large number of faults that run through the vent field. Many faults, especially at the south side, are high-angle normal faults that can be concealed by debris. Most of the vents found tend to run from east to west, likely due to the orientation of fault lines under the field. Two extinct fields are located about west and southwest of the central vent field at depths of or more. They have inactive vents similar in profile to Posidon with a talus (scree) deposit separating them from the central vent field, though they have not been as actively explored. It is hypothesized from the ages of samples collected that hot fluid flow migrated from the south to the north where Posidon currently resides. 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 Lost City older than all known black smoker vents by at least two orders of magnitude. Geology and chemistry Alkaline hydrothermal vents like those of Lost City are only superficially related to volcanic black smoker vents; the two types of vent are perhaps better described by their differences than their similarities. Though both types are often found near oceanic spreading centers, alkaline hydrothermal vents are not created by volcanic processes. They release methane and diatomic 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. Mineralogy The Atlantis Massif is described as an ultramafic oceanic core complex of the Mid-Atlantic Ridge, with upper mantle rock being exposed to seawater through faulting from tectonic extension associated