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Life on the Seafloor and Elsewhere in the Solar System

Life on the Seafloor and Elsewhere in the Solar System

If Volcanoes Plus Oceans Can Support Life at the Vents, Why Not on Other Planetary Bodies?


1998— The RIDGE program (Ridge Inter-Disciplinary Globe Experiments) was sharply focused on the global spreading center system, but the program’s goals were broadly defined. RIDGE was designed to explore the causes, consequences, and linkages associated with the physical, chemical, and biological processes that transfer mass and energy from the interior to the surface of the planet along the mid-ocean ridges.

That broad mission statement left a lot of room for the “I” in RIDGE. But one lesson of RIDGE is that truly interdisciplinary research is difficult to do. It is difficult to get funding for interdisciplinary research. It is difficult to overcome the language barriers across a spectrum of fields ranging from molecular biology to seismology. Nevertheless, the fields are related, and that is another lesson of RIDGE: Scientists must keep an eye on adjacent fields. Increasingly, a number of researchers believe that communication across fields will spawn some of the major scientific discoveries in the coming decades.

With that perspective, the RIDGE program might be considered a work-in-progress. Perhaps it is best viewed in the context of events that happened before it was initiated and activities that may take place as RIDGE evolves. We often look back in order to look forward, and looking back to the late 1970s, two major voyages of discovery occurred within months of one another. One voyage was to the bottom of the ocean and the other to the far reaches of the solar system. These discoveries set the stage for RIDGE.

In 1977, scientists using Alvin dove to the ocean bottom near the Galápagos Islands. They found evidence of volcanism, but, unexpectedly, they also discovered a lush animal community. An abundance of crabs, clams, mussels, and worms tipped with brilliant red plumes was found thriving near zones of active seafloor volcanism. Until then, the seafloor had been regarded as relatively barren terrain, where the only nutrient sources were scant dregs that percolated down from the sunlit surface. Distilled to its essence, this first discovery was that volcanic activity in the presence of liquid water can support life without sunlight.

Shortly after that Alvin dive, the Voyager I spacecraft set off to explore the outer solar system. Eighteen months later, it had reached Jupiter and, like Alvin, found something unexpected. As Voyager I flew past Io, the innermost moon of Jupiter, it photographed nine ongoing, simultaneous volcanic eruptions ejecting material hundreds of kilometers above the moon’s surface. Quite unlike the earth’s long-dead moon, Io turned out to be the most volcanically active body in the solar system. The second fundamental discovery, simply put, was that there were more volcanoes in the solar system than we had ever dreamed.

Two ideas, nearly 20 years old: Undersea volcanoes can support life; there are many volcanoes in the solar system. Only now are these two ideas beginning to interact with each other to guide exploration for life in outer space. But these ideas remained worlds apart when the RIDGE program was launched in the 1980s.

A primary goal of the RIDGE program was to look at events taking place on ridge crests in real time, rather than simply to map the products of those processes. From 1986 to 1990, Robert Embley and Edward Baker, from the National Oceanic and Atmospheric Administration (NOAA) Pacific Marine Environmental Laboratory (PMEL) in Seattle, Washington, and Newport, Oregon, identified likely volcanic activity associated with large water-column plumes along the southern end of the Juan de Fuca Ridge about 180 miles off the Pacific Northwest coast. But the link between the large plumes and an active eruption was mostly an insightful inference that could not be confirmed by direct observation. At the time, scientists on cruises involved in the area did note the presence of flocculated bacterial mats in the vicinity of fresh seafloor lavas.

In April 1991, researchers exploring the East Pacific Rise off the coast of Mexico found themselves in the right place at the right time. The cruise was led by Rachel Haymon of the University of California, Santa Barbara, and Daniel Fornari of Woods Hole Oceanographic Institution, who listened raptly as divers aboard Alvin reported near- whiteout conditions at the dive site. Clumps and clusters of what seemed to be bacterial products billowed up in huge plumes from beneath the seafloor. Through the bacterial haze, they saw tubeworms newly barbecued and folded in fresh lava. The researchers quickly drew the conclusion that the gods of serendipity had delivered them into the midst of either an active or a very recent eruption. These experiences substantially enhanced the resolve of RIDGE and NOAA vent scientists to pursue active events on ridge crests in real time.

With the end of the Cold War, oceanographers gained an invaluable tool: limited access to selected data from the Navy’s classified SOund SUrveillance System. SOSUS was an array of hydrophones originally designed to detect enemy submarines. On June 26, 1993, just four days after gaining access to some SOSUS data, Christopher Fox and colleagues at PMEL in Newport detected a series of earthquakes along the Juan de Fuca Ridge. In two days, the locus of earthquake activity had migrated 50 kilometers northward along the ridge axis.

The opportunity to catch a ridge eruption in flagrante finally had presented itself, but taking full advantage of the windfall was not automatic. Some in the scientific community still had doubts about this type of activity and viewed the effort as “fire-engine chasing.” Unlike the pursuit of fire engines, however, it is much harder to find ships (and funds) to pursue a possible eruption in the middle of an ocean. To arrive on site within days or weeks of an eruption was not easy. It meant persuading scientists to yield some of their hard-won ship time, usually scheduled more than a year before, to chase a possible chimera and either curtail or ignore their own funded research. Such behavior in the competitive, peer-reviewed world of oceanographic research could jeopardize longer-term funding for more predictable, if less exciting, science.

Nevertheless, within days, following a shore-to-ship call from Fox, Richard Thomson of the Institute of Ocean Sciences in Sidney, British Columbia, a member of the RIDGE Steering Committee, briefly redirected an ongoing cruise operating nearly 120 miles to the north. Thomson and colleagues discovered a major hot-water plume directly above the site where the migrating earthquakes had stalled. Embley and his NOAA colleagues, Baker and Bill Chadwick, also reacted within 10 days and redirected a long-planned cruise to what became known as the CoAxial Segment of the ridge. Using the Canadian vehicle ROPOS (Remotely Operated Platform for Ocean Science), Embley and colleagues found a fresh lava flow that already had been colonized with bright yellow mats of bacteria. Farther south, they discovered massive amounts of bacterial products surging from beneath the ocean floor, in a fashion strongly reminiscent of the East Pacific Rise event in 1991.

As these reports were relayed on shore, two University of Washington (UW) colleagues, Paul Johnson and Russell McDuff, and I worked with dispatch to request support from the National Science Foundation for RIDGE funds to explore the new eruptions with Alvin at the earliest possible time. Our argument was that for the first time ever we could approach a seafloor event with the full knowledge of what was taking place, when it began, what its extent was, and how it was unfolding. The submersible is nearly always booked, but there was an opening in October, four long months after Fox first detected the telltale seismic activity. By the time we put to sea with a scientific crew comprising both academic and NOAA researchers, we were already building on the work of many people: Embley, Baker, Haymon, Fornari, Fox, and Thomson. Then two others, Fred Spiess and John Hildebrand of the Scripps Institution of Oceanography, University of California, San Diego, contributed, on very short notice, an eleventh-hour sonar mapping program of the eruption area that helped guide our Alvin dives.

We found vast volumes of microbial material issuing from the seafloor, as had been observed before. But because of experience on previous expeditions, microbiologists from John Baross’ laboratory at UW were on board to culture bacterial samples that we collected. Then-graduate-student Jim Holden established that the volcanic microbes belonged to an ancient group of organisms that are so genetically distinct that they represent a separate and fundamental branch on the tree of life distinct from bacteria, plants, and animals. They are known as Archaea, or ancient ones, and they are hyperthermophilic, meaning they survive, in fact thrive, at temperatures greater than 90°C. We don’t know yet whether the eruptions flush pre-existing microorganisms inhabiting the subseafloor or whether the eruptions release nutrients that trigger a volcanic microbial bloom that simply overflows the available space in seafloor rocks. But it was clear that, as hypothesized earlier by Baross and his colleague Jody Deming of UW, the rocks below the seafloor are populated with microbial communities that we need to explore.

Discovering the outflow of Archaea along erupting spreading centers has been one of RIDGE’s major successes. It required long-term commitment and cooperation of many scientists in the face of considerable difficulty. Since the Coaxial Event, a number of similar rapid responses have been mounted to document these types of events, and in each case, high-temperature microbes have been cultured from the effluent associated with the volcanic-tectonic activity.

These observations are giving rise to a potentially controversial hypothesis: The brittle outer shell of any volcanically active, water-saturated planet may harbor a potentially vast subsurface microbial biosphere. Indeed, this deep, hot, chemically rich environment within the earth’s volcanic shell appears to have the necessary ingredients to foster the critical reactions that could have created the building blocks of life. In a 1983 paper, Baross, Sarah Hoffman, and Jack Corliss, all then at Oregon State University, first suggested that life may have originated on the earth not in warm, shallow pools struck by lightning, but rather in sunless, deep-sea volcanic vents. And if such an evolution can occur on the earth, perhaps something similar has occured elsewhere in the solar system where active volcanism and liquid water are juxtaposed.

One of the most intriguing solar bodies likely to support such life forms may be Io’s nearest neighbor, Europa—Jupiter’s second moon and one of the most beautiful planetary bodies in the solar system. It has a smooth, highly reflecting, almost pearl-like appearance from a distance because its surface is completely covered with ice and nearly devoid of large craters. Recent close-up images of Europa’s surface taken from the Galileo spacecraft display a more chaotic texture, which has been interpreted by the Galileo imaging team as a cluster of blocklike icebergs. The tops of these striated blocks appear to be “floating” about 200 to 250 meters above a surrounding slurry of much smaller ice fragments, much the way a large ice cube would float in a slush of crushed ice. The height of the ice block suggests that only one-ninth of its bulk projects above the surface. That implies that the blocks, which clearly have floated away from a solid ice “shoreline,” are about 3 to 5 kilometers thick. With a calculated bulk density of nearly 3.0 grams per centimeter, Europa must have a rocky interior, and the best estimates indicate that the water layer (whether liquid or solid) above the more dense rocky material is about 100 kilometers thick. If that is true, a relatively thin outer layer of ice may float atop a much thicker layer of liquid water, which directly overlies Europa’s higher-density interior. In other words, there may well be another ocean in the solar system, and it may be maintained by volcanism within the rocky interior.

Some scientists speculate that to maintain a liquid water body on a frigid satellite that is slightly smaller in diameter than the earth’s moon, Europa, like its neighbor Io, may harbor volcanic activity within. In Roman mythology, Jupiter, king of the gods, and the maiden Europa conducted a torrid affair. In a modern scientific parallel, the tidal relationship between the huge planet and its diminutive moon creates significant heat. Jupiter’s enormous gravitational embrace, combined with the resonant interplay of nearby satellites, alternately squeezes and stretches Europa, generating internal friction and possible volcanism, as it clearly does on Io. The possibility of a planetary body hosting both an ocean and submarine volcanoes makes similar systems on the earth useful analogs for searching for life elsewhere in the universe. By designing innovative strategies to learn more about the relationships between volcanoes and life here on Earth, we not only learn a great deal about how our own planet functions. We also gain valuable new insights into how to approach similar systems in our solar system and beyond.

John Delaney completed a degree in geology at Lehigh University in Bethlehem, Pennsylvania, before going to the University of Virginia for a master’s degree. As an ore deposit geologist in Maine, he became fascinated with processes that concentrate metals. Gravitating to the heart of the copper mining industry, he searched for base and precious metals in Colorado, Utah, Nevada, and Arizona, while studying economic geology at the University of Arizona in Tucson. After six months living in and working on active volcanoes of the western Galápagos Islands, he decided to study active volcanism for the rest of his life, and completed a dissertation on submarine volcanic gases.

His research and teaching have focused on active submarine volcano-hydrothermal systems along the global spreading-center network. In 1980 a unique set of rocks from the Mid-Atlantic Ridge recovered aboard Alvin provided clear evidence that seafloor fracturing and mineral deposition was identical to quartz veins beneath massive copper-iron sulfide deposits on land—bringing Delaney full circle to his original geological interests. The recognition that submarine volcanic gases provide an essential nutrient source for the microbial communities that are the base of the chemosynthetic food chain at ridge crests took another of his original research pursuits in an exciting, unanticipated direction.

Delaney enjoys the poems of haiku poet Matsuo Basho (1644-1694)—a master at capturing the essence of an experience in very few words:

Breaking the silence of an ancient pond,
A frog jumped into water.
Deep resonance!

Whether the pond is only a pond, or the pond is a mind and the frog is an idea, is left to the reader. In many ways, the simplicity and elegance of such a distillation is akin to what scientists strive to extract from their observations.