An Unprecedented Discovery: Life at the Seafloor
In 1977, a small group of oceanographers from Woods Hole Oceanographic Institute and Scripps Institute of Oceanography went into the eastern Pacific Ocean to look for underwater hot springs. They had aboard their ship a tiny submarine called Alvin, and its crew included Kathy Cane, a grad student, and Jack Corliss, a geologist. The team was hoping to find an explanation for some unusual deep-sea temperature data — probably originating from fissures along tectonic plate boundaries, nothing but hot water leaking from cracks in the Earth’s crust. Instead, they discovered hydrothermal vents: bizarre natural chimneys rising from the seafloor, each one a towering pillar of rock that spewed a never-ending plume of superheated fluid out into the depths of the ocean. This fluid deposits minerals on the crust as it emerges, building up the chimneys in much the same way stalagmites are formed in caves.
However, these vent structures weren’t the most fascinating part of their discovery. As the crew of the Alvin descended towards the seafloor, they were shocked to discover an abundance of life colonizing around the vents. These weren’t just sparse communities eking out a living in the darkness; they were thriving ecosystems of everything from seven-foot-long tube worms with bright crimson tips to massive clams, surrounded by colonies of smaller anemones, crabs, bacteria, and even a few fish. There were hundreds of species, and almost all of them were undiscovered.
In a lot of ways, finding these hydrothermal vent communities was like finding life on an alien planet. The seafloor, which is on average 3600 meters deep, is very different from most other places on Earth. It’s pitch black and frigid, and the pressure is high enough to crush a human being under its weight. The harsh nature of the environment means that, for the most part, very little can survive, and anything that can withstand the pressure and the temperature is still left without sunlight. Photosynthesis, the process by which plants take in energy from sunlight and convert carbon dioxide into sugars, is impossible in these conditions. For a long time, the scientific community thought there was no way for life to exist without sunlight. Hydrothermal vent communities were living proof that — somehow — this wasn’t true. So where did these ecosystems get their nutrients?
As it turns out, organisms in the deep sea have adapted a process known as chemosynthesis, which is analogous to photosynthesis but relies on the unique chemistry of hydrothermal vents instead of on the energy of the sun.
When hydrothermal vents form, they do so along the divergent boundaries of Earth’s tectonic plates, in areas where the crust is slowly spreading outwards. As the crust expands, seawater seeps into the cooled, porous rock at the surface until it nears the rising magma. The water heats up to about 750° Fahrenheit — for reference, water boils at 212° Fahrenheit — and starts to expand and dissolve minerals from the surrounding rock, including metals like iron, copper, and lead. Eventually, it pushes back out through the crust as superheated, mineral-rich fluid. The chemicals expelled by the vents often lack carbon, a necessary component for photosynthesis and the basis of many ecosystems’ food webs, so the microbes here are adapted to take in nutrients from compounds which are present, like hydrogen sulfide, ammonia, and ferrous iron. These microbes may live on their own or in the tissues of other hydrothermal vent organisms, ensuring that the entire community has access to the nutrients.
This year marks the fortieth anniversary of the discovery of hydrothermal vents, but there are many things about their role in the global ecosystem that we are still learning. One of the most valuable roles hydrothermal vent communities play may be in the mitigation of climate change, as they absorb large quantities of methane — a potent greenhouse gas — that is released by the vents. Unfortunately, drilling and mining operations at these sites threaten to upend the ecosystems. Because hydrothermal vents are hidden away in the depths of the sea, their plight is easily swept under the rug; without a concentrated effort from conservationists on an international scale, these communities may become endangered before we can even begin to comprehend their value.
