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 Tube worms.

 Giant clams.

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"Black Smokers"

by Kathy Svitil

In the frigid depths far beneath the ocean surface, at the ridges where new crust is born, lies a landscape more alien than earthly. Here, strange long-necked barnacles, giant clams, and bizarre worms, their blood-red gills fanned out of bodies like bone-white tubes, clump beside towering spires of mineral. Nearby, sooty black clouds billow out from fissures in the seafloor, and organisms swim by, glowing with their own, otherworldly light.

The setting for this surreal scene is the submarine hydrothermal vents of Earth's mid-ocean spreading ridges. At the mid-ocean ridges, molten rock bubbles up from the mantle to the sea floor and cools to form new oceanic crust. Cold sea water percolates down through the fissures in these ridges, and many types of minerals -- like sulfur, copper, zinc, gold, and iron -- are transferred from the hot, new crust into the water.

The water, now rich with dissolved metals, is heated and then gushes back up through the cracks, forming hydrothermal vents. As the hot water -- which can reach temperatures of over 700 degrees Fahrenheit -- escapes from the vents and comes in contact with the near-freezing water of the ocean bottom, the metals quickly rain out of their solution. The result are surging clouds of particle-rich water called "black smokers," which often erupt out of tall chimneys of previously deposited solidified mineral.

Such hydrothermal vents were predicted long before they were first discovered by the submersible Alvin in 1977, as it surveyed the Galapagos Rift, along the eastern Pacific Ocean basin and over a mile and a half below the surface. (Other active systems being studied include the Juan de Fuca Ridge, off the coast of Washington and Oregon, and the Southern East Pacific Rise, in the middle of the southern Pacific Ocean.)


A "black smoker" in the East Pacific, discovered by the submersible Alvin.

Because so much metal is spewed out, hydrothermal vents have been responsible for many of the world's richest ore deposits, like the copper ores mined on the island of Cyprus in the Mediterranean Sea. Indeed, many economic geologists have suggested that active vents -- not just the sites of former ones -- be mined for their massive metallic deposits, although their remote locations might make that difficult.

The vents are also remarkable for their unusual, diverse life forms, like the tube worms, giant clams, and long-necked barnacles. Life is possible at the hydrothermal vent systems because of a unique type of bacteria that forms the basis of the food chain there. The bacteria harness energy not from the rays of the sun -- no sunlight reaches these great depths -- but by metabolizing the large amounts of sulfur in the hot springs.

Some researchers believe that life on Earth began in extreme environments such as these submarine hydrothermal vents. If hydrothermal vents are now (or once were) present on other worlds -- Europa, Jupiter's ice-covered moon, is one possibility, as is Mars, where minerals that on Earth are commonly formed at hydrothermal vents were just discovered -- life might very well have arisen there too.

Photo: Dudley Foster. Courtesy of the U.S. Geological Survey.

Article: The Earth at Work | Sidebar One: Probing the Depths | Sidebar Two: "Black Smokers" | Sidebar Three: Ring of Fire | ANIMATION
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