deep within the vents, precipitated in the cooler surroundings. Clams, giant specimens, measuring a foot or more in length, along with similarly outsized brown mussels, appeared to be bathed by the simmering water. Alvin's robotic arm, which had been expected to grasp only rock samples from the bottom of the Galapagos Rift, now was pressed into service to grasp samples from this most remarkable community of shellfish. When we planned this cruise, our thoughts had been so far from biology that we had brought no preserving medium along. Some of these samples thus made the trip back to shore immersed in vodka.

Over the coming days, the expedition' s researchers took turns scouring the rift for similar signs of life. With guidance from Angus, these rovings in Alvin bore rich rewards. We eventually identified five sites that teemed, or had recently teemed, with creatures as bizarre as they had been unexpected. We termed our initial find "Clambake I" and also located a site we called "Clambake II," where a change in conditions had killed off the big bivalves and left only a midden of shells. The "Oyster Bed" was our label for a patch of mussels, miss-identified as oysters°our flawed attempts at taxonomy went temporarily unchallenged, since there were no biologists along on the expedition°and another site was dubbed the "Dandelion Patch,'' because it was home to a population of hitherto unknown animals resembling bright yellow dandelions, attached to the bottom not by stalks but by delicate fibers. Finally, there was the "Garden of Eden," lushest and most varied of these strange oases. Here were the dandelions, along with white crabs, limpets, small pink fish, and clusters of vivid red worms that protruded from their own long, stalk-like white tubes. The tube of a specimen later brought to the surface measured more than two meters in length, with the animal itself filling more than half of its elongated tube.

The obvious question in everyone's mind was what enabled these colonies of creatures to flourish at such depths, in an atmosphere totally devoid of sunlight? The answer quickly came, on board Knorr, with the analysis of water samples taken by Alvin at the vents surrounded by the oases. The first thing noticed, when the sample containers collected by Alvin were opened, was a pervading odor of rotten eggs: hydrogen sulfide. This was the clue that enabled us to piece together the chemical and biological processes that made possible the huge clams, tube worms, and other life forms in such high concentrations.

The earlier suggestions of Lister had been shown to be true. The deep fissures in the floor of the rift allowed cold seawater to penetrate Earth' s crust, down to the level of hot, newly formed layers of rock surrounding the magma chamber. The temperature of the water rose as it flowed deeper, and its chemical composition changed. The seawater exchanged some of its chemicals with the subsurface rock and leached out others. The sulfate in the water was changed to hydrogen sulfide°hence the telltale smell in the lab. Finally, the heated water rose back to the seafloor through other fissures in the crust and raised the ambient temperature of the vent oases to the surprising levels recorded by Alvin.

Living inside the macrofauna of clams and tube worms were hydrogen sulfide-oxidizing bacteria that formed the basis of this unique food chain. In the case of the clams, the available nutrients were abundant enough to lead to gigantism. Clambake II, in the light of this analysis, appeared to have been an oasis chilled and starved into extinction as the recycling of seawater through the vents had ceased for some unknown reason.

We had discovered something new upon Earth. Prior to our investigation of the hydrothermal vents along the axis of the Galapagos Rift, all forms of life had been assumed to be dependent upon photosynthesis, the process by which sunlight is metabolized to sustain the growth of plants and animals. Even the holothurian, living at great depths in a sunless world, depends for its survival upon organic material that drifts down from the sunlit surface. But within the vent field, for the first time, was evidence of a community of animals subsisting on a process of chemosynthesis, beginning with the metabolizing of hydrogen sulfide by microorganisms. They were, after all, creatures that needed no sunlight at all for survival and that owed their existence to the warmth and chemical sustenance of Earth itself.

Two years later in 1979, marine biologist Fred Grassle and I co-led a second expedition to the undersea oases of the Galapagos Rift. Fourteen other biologists accompanied us— this time, there would be no relying on vodka for preserving specimens. We also brought a film crew from the National Geographic Society, which chronicled our discoveries in the television special "Dive to the Edge of Creation." This time, the challenge we faced was quite different from our 1977 task. Then, we were looking for hydrothermal vents and had no idea of the oases. Now, we were trying to locate the same sites we had visited before, in a place where there were no identifying landmarks either above or beneath the surface.

As before, we deployed Angus as our eyes and temperature sensor prior to a manned investigation in Alvin. Reviewing the thousands of frames exposed by Angus's cameras on the sled's first run along the rift floor, we began to resign ourselves to a long search. Then, with about four frames to go, we found what we were looking for. Angus had photographed a clutch of our mysterious dandelions, and we knew we were in the right spot.

Taking our turns in Alvin, we explored a string of new vents and their surrounding oases, including the largest discovered on either of the two expeditions—an otherworldly habitat for tube worms 2 to 3 m long. And with our complement of biologists and biochemists, we were able to achieve a far more sophisticated understanding of the processes involved in sustaining the creatures of the oases and to make an attempt at classifying them.

Beyond a doubt, it was the chemosynthesized nutrients that made the oases possible. The warmth of the water itself was not a primary factor; there are animals that survive the