Life that lives off the Earth's energy

An unusual environment for life exists deep in the oceans.  Where hot springs emerge on the ocean floor, a microbial community flourishes, living off the hydrogen sulfide and other compounds carried by the venting fluids.  Some of these microbes represent the most ancient life known, and they form the base of a food chain for a group of organisms that never see the light of the Sun.  Life may have begun around these deep hydrothermal vents.  If similar environments exist elsewhere in the solar system, they too may support life.

Sulfide chimneys from the Juan de Fuca Ridge
At the Juan de Fuca Ridge and elsewhere along the global system of mid-ocean ridges, the heat from intrusions of magma, or molten rock, causes seawater to circulate through the cracks in the rocks.  Sulfide chimneys build up around vents where the hot water returns to the ocean.  The underwater hydrothermal systems influence chemical composition of the ocean, and the venting hot waters and structures that build up around the vents illustrate how certain ore deposits formed. 

The Juan de Fuca Ridge
Two kilometers under the Pacific Ocean, where the Pacific and Juan de Fuca plates meet, lies a strange landscape with clusters of towering sulfide chimneys forming around vents of hot, mineraladen water.  The rocks harbor a little-known microbial community that thrives on chemicals in the hot water.  In 1997 and 1998, the American Museum of Natural History and the University of Washington sent an expedition to the Juan de Fuca Ridge.  Its goals were to bring back several active chimneys, to study how they grow, and to determine the nature and distribution of life inside them. 

Godzilla

The largest sulfide chimney ever found was from the Juan de Fuca Ridge.  It stood 47 meters high and was named Godzilla by the scientists who discovered it.  Godzilla collapsed into a heap of rubble in 1996, but by the next year, a second spire, about 20 meters high, had grown in its place.  Great amounts of mineral-laden hot water must circulate in the crust for such massive structures to form.  About 80 percent of the Earth’s internal heat escapes through the ocean ridge system.

The sulfide chimney displayed here were named for charaters in Irish mythology: the warrior Finn MacCool, Gwenen, Guinevere’s lusty sister, and Roane (Gaelic for “seal”), one of the fairy people.

The water flowing through this chimney was 302 degrees Centigrade. As this superheated water mixed with the cold ocean water, a dense black cloud of precipitating minerals formed. After the chimney was collected, the stump grew nearly 3 meters in three weeks, owing to the large amount of hot water flowing through it. The yellow, metallic mineral lining the channel inside the chimney is chalcopyrite, a copper-iron sulfide. The small black crystals are the zinc-iron sulfide mineral wurtzite, and the white mineral is the calcium sulfate anhydrite. The black walls of the chimneys are made of a mixture of iron sulfide and oxide minerals and silica. AMNH collection

Juan de Fuca Ridge, northeastern Pacific Ocean These are two halves of the top of Gwenen, a five story-high spire that was venting water at 179 degrees Centigrade. It bristled with a profusion of tube worms and other animals, vestiges of which can still be seen on its surface. The microbes on which these animals lived were sustained by the hot, nutrient-rich water that leaked out the sides of the chimney. As the chimney grew, built up irregularly by minerals precipitating from the water, animals were trapped and buried in the walls. The holes on the left are places where core samples were taken for study of the microbial community that once lived in the chimney.
AMNH collection

Modern black smokers, like ancient black smokers, contain complex mixtures of fine crystals of iron, copper, and zinc sulfides. The images to the left are high-magnification views of the polished surface of a piece of Finn, one of the sulfide chimneys collected for this exhibition. AMNH collection

Roane contains a complex series of interconnected channels and isolated voids. Some of the channels are lined with the yellow, metallic copper-iron sulfide chalcopyrite, which forms only at temperatures approaching 300 degrees Centigrade. The small black crystals lining most of the channels are the zinc sulfide wurtzite, which forms at a lower temperature. The temperature of the water seeping from the top of Roane was 196 degrees Centigrade.
AMNH collection