Notes

Like hot springs and geysers on land, hydrothermal vents form in volcanically active areas—often on mid-ocean ridges, where Earth’s tectonic plates are spreading apart and where magma wells up to the surface or close beneath the seafloor. Ocean water percolates into the crust through cracks and porous rocks and is heated by underlying magma. The heat helps drive chemical reactions that remove oxygen, magnesium, sulfates and other chemicals from the water that entered the ocean through rain, rivers, and groundwater. In the process, the fluids also become hotter and more acidic, causing them to leach metals such as iron, zinc, copper, lead, and cobalt from the surrounding rocks. The heated fluids rise back to the surface through openings in the seafloor. Hydrothermal fluid temperatures can reach 400°C (750°F) or more, but they do not boil under the extreme pressure of the deep ocean.









As they pour out of a vent, the fluids encounter cold, oxygenated seawater, causing another, more rapid series of chemical reactions to occur. Sulfur and other materials precipitate, or come out of solution, to form metal-rich towers and deposits of minerals on the seafloor. The fluids also contain chemicals that feed microbes at the base of a unique food web that survives apart from the sun. Instead of relying on photosynthesis to convert carbon dioxide into organic carbon, the bacteria use chemicals such as hydrogen sulfide to provide the energy source that drives their metabolic processes and ultimately support a wide range of other organisms such as tubeworms, shrimp, and mussels.