Searching for Life Where the Sun Donít Shine (part 1): Explorations to the Sea Floors of Earth and Europa
Images and data received from Voyager 2 suggested that beneath that layer of water ice lies a liquid water ocean bigger than all of Earth’s oceans combined covering the entire moon—itself about the same size as our own moon.
Soon researchers began to wonder if, beneath that layer of ice at the bottom of thousands of feet of water and methane liquid, the seafloor there smelled like rotten eggs, too.
At 8:00 a.m. Friday, January 6, 2012, German began perhaps the most promising research expedition of his 28-year career. He watched from the deck of the research vessel Atlantis as his team and crew totaling nearly fifty people embarked from Port Everglades, Florida. The last shipment of equipment had only narrowly arrived with half an hour to spare before the ship’s departure, culminating years of preparations for this expedition. Atlantis headed south, passed the Florida Keys in the late afternoon, and turned west, following a backwards S route that would take the team around the western end of Cuba to a stretch of ocean above a 70-mile long ridge in the seafloor called the Mid-Cayman Rise (MCR). Their target: new hydrothermal vent sites along the ridge that German and colleagues had explored and mapped during two prior survey expeditions in 2009 and 2011. Dubbed “OASES 2012: Return to the Cayman Rise,” this research expedition was chronicled by Julia DeMarines, a research assistant of the astrobiology curator at the Denver Museum of Nature and Science.
Hydrothermal vents happen where near-freezing water at the bottom of the ocean meets the scalding hot rocks of young ocean crust. At mid-ocean ridges like the Cayman Rise, magma is produced by a heat source that comes from energy released from the decay of radioactive materials deep inside the planet and also leftover heat from the Earth’s formation. When water and hot rocks meet, the now superheated water shoots up through cracks in the seafloor, creating plumes of hot gases and chemicals that can reach several hundred feet in height. The plumes are often black and sooty—the ocean version of a diesel train engine belching a steady stream of black smoke into the sky. This gives rise to the nickname black smoker. This mix of hot chemical-laden fluids and cold seawater creates conditions that form the ocean equivalent of a desert oasis.
These sites host communities of living matter that can be denser than any patch of life on land in the known biosphere and 10,000 to 100,000 times greater than the rest of the seafloor. Here, exotic tendril-like organisms called tubeworms can grow eight feet tall and clams can be a foot across. Normally, clams a third of an inch across are a century old. Yet, at some plumes, clams nine inches across are just ten years old. That means their growth rates are 300 times faster than those of clams anywhere else on the seafloor.
Yet, life thrives at hydrothermal vents. They’re also diverse by location—just like distinct biogeographic regions on land. Life forms found in one ocean can vary significantly from those found in another ocean. The 2011 cruise had been especially productive in proving the amazing diversity of life near these extraordinary sites. German had personally witnessed the discovery of the first live tubeworm found near a hydrothermal vent in the Atlantic Ocean. Bigger still, that team had found chemosynthetic shrimp (which live off energy from chemical reactions from the vents instead of photosynthetic processes involving the Sun) and tubeworms occupying the same site—perhaps the landlubber equivalent of finding a lion and a polar bear chewing on the same antelope in the middle of the Sahara.
Now the team was heading back to the MCR to collect the first physical samples from what some consider the most interesting collection of hydrothermal vents on our planet.
The first, Type 1, is common throughout the world’s mid-ocean ridge system and is characterized by high temperatures (sometimes more than 400 degrees Celsius) and “mafic” rocks from the Earth’s crust, meaning they are rich in magnesium and iron. Type 2 vents have similar high temperatures, but these vents are the result of reactions between seawater and far deeper rocks from the Earth’s mantle with even higher concentrations of magnesium and iron. These are classified as “ultramafic.” Type 3 vents, too, are ultramafic but have much lower temperatures. Since they’re hosted in rocks formed at even higher temperatures than what erupts at the seafloor today, they are directly comparable to material that erupted on the early Earth. As such, ultramafic vent sites are among the most exotic and captivating of hydrothermal environments to marine scientists.
Chief Scientist German had found evidence for at least three vent sites during his first trip to the MCR in 2009. Past experience in the southern Indian and Arctic Oceans had tempered expectations for discovery of new vents sites to no more than roughly one site for every 100 miles of mid-ocean ridge explored. Since the MCR was only 70 miles long, that first voyage was “probably the highest-risk expedition I have ever undertaken,” says German. The probability of finding even one vent site there was fairly low to begin with.
Thus, finding three sets of plume signals in those original water-column studies, indicative of three different types of venting on the same relatively small stretch of mid-ocean ridge was astounding, a bit like looking for a coffee shop and finding a Starbuck’s, a Dunkin Donuts and a Caribou Coffee on three corners of an intersection of a two-road town in the middle of a Nebraska cornfield. That’s why, in the world of hydrothermal vents, there’s more than one reason why this specific stretch of seafloor real estate is considered a “hot spot.”
Unfortunately, the team’s original discovery was followed closely by setback. The 2009 expedition was cut short by Tropical Storm Irene before the team could get up close to any of the prospective sites with its Remotely Operated Vehicle (ROV), Nereus. German had to wait until the 2011 opportunity to get a closer look, but this 10-day expedition was only intended to photograph and map the vent sites. No samples were collected. Both expeditions paved the way for the 2012 expedition, which would be the first to study each site in detail and to obtain actual samples of the rocks, water, tubeworms, and other critters in the vent communities.
“Just like the Hubble Telescope, pointed at the most distant points of the Universe, hydrothermal sites like these may become a sort of lens that allows us to view back into Earth’s distant past and explain how life originated on Earth,” says German.
And just like the Hubble Space Telescope, his expedition is funded significantly by the agency largely responsible for directing our eyes skyward: the National Aeronautics and Space Administration.