Searching for Life Where the Sun Don’t Shine (part 2): Explorations to the Sea Floors of Earth and Europa
This is Part 2 of a 6-part series that tells the story of humankind’s efforts to understand the origins of life, by looking for it in extreme environments where life thrives without relying on the Sun as an energy source. This series follows an oceanographic expedition to the Mid-Cayman Rise, led by Chris German of the Woods Hole Oceanographic Institution, and NASA’s efforts to plan a future mission to Jupiter’s moon, Europa. By understanding how life can live without the Sun, we may discover how life began on our planet, and whether or not Earth is the only place in the universe capable of supporting a biosphere.
Just as it helps Chris German answer riddles about the origin of life on Earth, life’s surprising hardiness gives astrobiologists cause for hope in finding life on seemingly inhospitable hells off Earth, too. Among researchers on the search for those hells is Steve Vance, a member of the Science Definition Team for NASA’s Europa missions. As Chris German and the crew of Atlantis set out to scoop up evidence for life on the bottom of Earth’s seafloor, Vance met with a team of engineers and planetary scientists at NASA’s Jet Propulsion Laboratory (JPL) to plan a mission with a similar objective yet radically different destination. Their goal: to find out if there’s hydrothermal vent-like life on Jupiter’s moon, Europa.
Vance and his colleagues are busy planning a mission to send a robotic spacecraft to gather more data on the icy moon to determine whether life once existed (or still exists today) in an ocean below the surface-covering layer of ice there. Based on data from Voyager and, later, the Galileo robotic flyby missions, scientists think there could be similar geologic processes on Europa’s seafloor as we find on our own seafloor. If so, there’s reason to believe life could be thriving today in the cold, dark depths there, huddled around oases of hydrothermal vents just like on Earth. That’s why, to people like Vance, Europa’s at the intersection of life where space and ocean exploration come together.
Traditionally, the search for life beyond Earth has been focused on a region surrounding the Sun (or in the case of other solar systems, another star) where a planet or moon with sufficient atmospheric pressure can maintain liquid water on its surface. This is based on the assumption that life elsewhere beyond Earth would be a lot like life found on our planet — particularly, that liquid water would be essential to its survival. The search for the right conditions for life involves finding a planet or moon in a location that isn’t too close to its host star to boil off any liquid water or too far from the star to keep all water in its solid ice phase. This is what astrobiologists and astronomers refer to as a “Goldilocks planet” — one that’s not too big, not too small, not too hot, and not too cold — but just right.
Except, Europa isn’t a Goldilocks planet. It lies well outside the supposed habitable zone of our solar system (which conveniently only includes a region of space containing Earth and our moon). So how could life possibly survive on Europa?
The answer lies in how life gets its energy. More than 99% of life on Earth gets its energy from the Sun. Plants get their energy from photosynthesis, which produces oxygen. Animals breathe this oxygen and eat the plants. Other animals eat those animals. Then animals die and become nutrients in the soil for plants, thus completing the extraordinary, miraculous circle of life as we know it.
But hydrothermal vents demonstrate that not all life needs the Sun to serve as the stork. The remaining less than 1% of life just needs a little bit of superheated water cooked up by rocks deep within the Earth to generate the right blend of rotten egg-smelling fluids that can then be combined with near freezing seawater at bone-crushing depths to allow them to survive.
Simple enough, right?
The process of obtaining energy from chemical reactions between water and the young underlying seafloor rather than sunlight is called chemosynthesis. In the case of hydrothermal vents, the primary compound is hydrogen sulfide. This chemical process is the reason why NASA’s interested in hydrothermal vents on Earth’s seafloor. And if chemosynthetic life exists anywhere outside of Earth, Europa would be a good place to start looking for it. The sixth closest of Jupiter’s moons, Europa may be one of the few places in our solar system where chemosynthetic life not only could have lived in the past, but might still be thriving today. If there’s water and the moon is as thermally active as scientists think, the conditions might be just right to sustain an alien ecosystem.
Vance and his colleagues at JPL are hoping to be the first to find that alien ecosystem. They’re currently working on a proposal to launch a mission to Europa in 2020, which could reach the icy moon by 2026. It’s a long time to wait, but such is the reality of conducting research on a subject 500 million miles away.
This is where the explorations of the very high meet those of the very low. And there may be no greater connection—or common purpose—between exploration of the heavens and the depths of our seas than in the search for life and its mysterious origins.
Before 1977, biology textbooks claimed that to sustain a living ecosystem, you needed energy from the Sun. That was before Donnelly, van Andel, and Corliss dove to the bottom of the sea in Alvin as part of the Galapagos Hydrothermal Vent Expedition.
Their mission didn’t have anything to do with rewriting biology textbooks. Van Andel, a geo-archaeologist, and Corliss, a geologist, were more interested in the seafloor itself. Scientists had speculated the existence of hydrothermal vent systems, but no one had ever proven they were there and certainly no one had seen them in person. Their speculation stemmed from heat-flow calculations along the 42,000-mile global mid-ocean ridge system—a planet-wide mountain range that forms the largest geographic feature on Earth and snakes around the seafloor like the seams on a baseball. This underwater mountain range marks the line where Earth’s tectonic plates are spreading apart from each other—the same phenomenon behind the suspiciously similar coastlines of South America and Africa that make the jigsaw-like continents appear to have fit snugly together at one time. Well, they did. That is, before seafloor spreading pushed them apart over millions of years at a rate about as fast as your fingernails grow, creating gaps in the ocean’s bottom along the ridge where new crust from the planet’s mantle oozed upwards, cooled, and formed brand new seafloor.
Scientists made heat-flow calculations to characterize what this new crust should look like. Clive Lister, a geophysicist at the University of Washington, argued that since the young crust coming up from the mantle was being cooled by the near-freezing ocean water, it should cool and contract the farther it got from the ridge. That meant the hottest spots should be near the ridge. Yet, when actual heat-flow measurements were made at portions of the seafloor up to several hundred miles out from the ridge, everything looked right except for those spots nearest the ridge. They weren’t as hot as they should have been. Where was the missing heat?
Lister speculated that the ridge was essentially a giant heat blister. Molten rock chambers at temperatures of 1,200-1,400 degrees Celsius lay below the ridges and cracks in the seafloor allowed cold water to seep into the crust. Where cold water met hot magma, the water expanded, became superheated and shot back up to the surface in the form of underwater hot springs, or hydrothermal vents. This is where he thought the missing heat might be going.
At least that was the going theory as Donnelly steered Alvin down into the darkness. He, van Andel, and Corliss were on the search for missing heat.
Enclosed in an almost seven-foot diameter titanium pressure sphere, the three men huddled together behind walls less than two inches thick. At a depth of 9,000 feet, they had long since passed the point where the Sun’s rays penetrate the sea (roughly 3,300 feet). The water pressure at this depth is nearly 300 times higher than at sea level, which meant that every square inch of the hull felt about the same as your big toe would feel with the weight of an entire Jeep Wrangler pressing down on it. “If seawater with that much pressure behind it ever finds a way to break inside, it explodes through the hole with laser-like intensity,” wrote legendary oceanographer Bob Ballard in The Eternal Darkness. Ballard was the co-chief scientist of the Galapagos Hydrothermal Expedition (along with Richard von Herzen) and was onboard the support ship, Knorr, while Donnelly patrolled the seafloor in Alvin. “A human body would be sliced in two by a sheet of invading water, or drilled clean through by a narrow (even a pinhole) stream, or crushed to a shapeless blob by a total implosion,” wrote Ballard.
The crew relied completely on Alvin’s quartz iodide and metal halide lights to illuminate their path through the darkness. To navigate, Donnelly used three transponders—which the team named Sleepy, Dopey, and Bashful—that had been dropped five days earlier in a triangular pattern at various points in the area. Unlike airplanes, which use light and radio waves to navigate, submersibles need to rely on sound waves (just like dolphins) to figure out where they are and where they’re headed. Light and radio waves can’t travel very far in water. Alvin’s navigation computer sent out sound waves toward the transponders, which in turn, sent back sound waves of their own. Based on the data from the transponders, Donnelly was able to steer Alvin toward the team’s target location on the seafloor.
Their intended target had been identified two days earlier, when the Knorr had located a spike in water temperature near the seafloor. The research vessel had been dragging a camera sled called ANGUS (Acoustic Navigated Geological Undersea Surveyor) outfitted with a sensitive thermistor capable of picking up tiny temperature changes in the water. Operators on Knorr needed to keep ANGUS 15 feet above the seafloor—a difficult task given the varied landscape of the rugged, volcanic terrain.
Good thing ANGUS’s toughness matched the motto on its side: “Takes a Lickin’ But Keeps on Clickin’.” Despite occasional collisions, operators were able to maneuver the 2-ton steel sled over seven miles of seafloor real estate in a 12-hour span. Only one three-minute period of trawling had yielded anything significant.
When the team reviewed the photos the next day, they were shocked at what they saw. Thirteen photos taken during that three-minute interval revealed an incredible accumulation of life—mostly in the form of white clams and brown mussel shells—that no one had expected to see. Living communities this deep had never been seen before. The deep ocean floor was supposed to be devoid of life.
Van Andel and Corliss sat with eyes peeled out the sub’s 4.5-inch circular viewports. Not only were they looking for heat in a cold, barren abyss, they were now on the search for life.
As Donnelly zeroed Alvin in on their target, formations of long-cooled, hardened lava “pillows” were all they could see. These had been formed as cracks emerged in the crust, caused by the seafloor spreading. The cracks allowed magma to spew from the Earth, cool, and form mounds as if the planet had squeezed hundreds of tubes of toothpaste from its belly and failed to utilize any of it.
Alvin inched closer and the team noticed the lava patterns began to change—appearing smoother and shinier as they approached the target. These lava flows were sinewy and suggestive of faster, fresher flows. They were getting closer.
When at last they reached the coordinates of the temperature spike, the crew entered an alien world. The dark water shimmered blue from manganese and other minerals carried up through the crust by superheated water. Clams measuring a foot or more in length piled high surrounded by shrimp, crabs, fish, and small lobster-like creatures. Strange plant-like organisms grew from the rocks, appearing like dandelions, and bizarre, wormy tendrils reached out from clumpy harbors.
“Isn’t the deep ocean supposed to be like a desert?” Corliss asked a graduate student on the support ship Lulu by acoustic telephone.
It was. Until now.
Not only had the team found their missing heat by discovering the first hydrothermal vents, but they’d also stumbled upon something else, something potentially even more profound. “A suspicion dawned on us,” reported Ballard. “These unexpected life forms might actually be a bigger discovery than the expected warm water.”
When Donnelly brought Alvin back to the surface, the research team struggled to figure out what to do with their unexpected biological samples. They hadn’t prepared for living samples. They thought they’d be dealing with rocks. They didn’t even have a single biologist onboard (only geologists, geophysicists, chemists, geochemists, physicists, and one lucky science writer).
A small amount of formaldehyde and some Russian vodka the team had picked up in Panama were the only preserving liquids they could come up with. Over the next several days, the team found four more vent sites, each unique from the previous one. They came up with names for each site—Clambake I, Clambake II, Oyster Bed, Dandelion Patch, and, finally, the Garden of Eden.
The discovery of these sites was applauded throughout the scientific community. Biologists were eager to find out just what sort of life could live in darkness on the bottom of the ocean. Hydrothermal vents and the ecosystems they generated would come to redefine the making of the planet and our theories about how life began here. But first, there was the issue of the rotten eggs smell.