The mysterious love child of geology and biology: Hydrothermal Vents - Part 2

A Discovery of Significance

In 1977 geologists made a discovery that changed the way we think about life on this planet. On a geologic research cruise to find places on the deep sea floor where the Earth’s crust was pulling apart (divergent plate boundaries) and study newly formed sea floor they found unbelievable assemblages of species. In this environment, thought to be devoid of life due to the lack of sunlight, they found diversity and richness that rivaled the tropical rain forests. There had been previous indications of life in these deep wastelands, but no one had expected that a significant amount of life could exist in the deep. Huge clamshells had appeared on videos of the deep taken by a robotic camera guided. This camera was attached to a Remotely Operated Vehicle (ROV) but the footage was dismissed as an anomaly. It wasn’t until scientists themselves physically went down to the deep in mini-submarines called submersibles, and saw thriving communities with their own eyes, that the concept of significant life on the sea floor became a reality.

People who have been down to see the vents in submersibles describe it as a totally surreal experience. A slow and erie descent through darkness punctuated by layers of neon light shows, much of which can not be caught on film. Dr. Bob Ballard was one of the scientists on the 1977 expedition that discovered the vents. He described it as follows

“We didn’t know we were going to make this discovery. I mean, my god, thats what makes it so amazing. We thought we’d find a crack in the ocean with water coming out. Big deal: that’s what surprised us. We didn’t know this was going to be as gigantic a deal as it was.”

These communities were something people had to experience in order to believe because it was contrary to what we thought we knew about life. The vast majority of exciting Eureka! moments in science happen in a lab. This discovery was so fundamental that it happened out at sea on a ship, rather than after samples had been processes and analyzed. The thrill the geologists on board felt at encountering something so novel, must have been something like what Charles Darwin felt when he came across creatures in the “new world” unlike anything he had seen before. There are few places on land where this type of encounter can still being had. The deep sea represents one of the last environments on Earth where the scientists can still be considered Explorers.

Prior to the discovery of deep sea hydrothermal vents, it was understood that all life on Earth was dependent on the sun, and could not survive without it. Period. It may seem that the existence of these verdant deep sea communities is little more than a bizarre exception to this rule. However, their existence forced a scientific re-evaluation of life and its evolutionary history on this planet (and potentially others) on par with the re-evaluation of the planet that occurred when early scientists realized that the world was not flat.

Living things are primarily divided up into producers (who make their own food), consumers (who eat other organisms), and decomposers (who break down dead organisms). It had been assumed and taken for granted that all producers made their food by converting the sun’s energy into sugars such as glucose through photosynthesis. Maple tree sap that becomes maple syrup is a clear example of this process. Producers form the base of all food chains and they tend to be present in ecosystems in far greater amounts (either in terms of numbers or overall volume of organisms) than the consumers. In a simplified view we can think about a single carnivore like a bald eagle. It feeds on animals such as snakes or fish which in turn might feed primarily on insects. If all of those insects fed only on grasses, you could imagine that a huge grassy field would be necessary to form the base of the food pyramid supporting a singe eagle. In the ocean it is much the same except instead of plants the surface waters are full of microscopic plankton that perform photosynthesis (phytoplankton) as well as slightly larger animal-like plankton (zooplankton) that eat the plant-like phytophankton and in turn feed smaller fish who feed larger fish and so on and so on. The one glaring exception to this is can be seen in the largest organisms on the planet. The baleen whales (such as Humpbacks) who filter unimaginable numbers of krill (shrimp-like invertebrates who feed on plankton) from the ocean on a daily basis. The blue whale is the largest animal that has ever lived on the planet, and it is able to grow as large as it does because it feeds low down on the food chain on organisms that are found in great abundances. If it had to swim quickly after fish it would not be able to eat enough to meet its energy demands.

The sun’s light energy does not penetrate more than a few hundred meters below the ocean’s surface, and because of this it was assumed that producers would not be found in any abundance at depth in the ocean. Up until the early 1980’s it was thought that the only creatures in the dark mysterious world covering most of our planet’s surface were solitary strange fishes that feed on each other or the organic debris that continuously rains down from the upper layers of the ocean where it was generated (directly or indirectly) from the sun’s energy. These alien organisms (and they really do look like aliens!) with their own lights to lure in prey, or jaws able to open far wider than their head to consume large prey were known, but they are few and far between. The world that people imagined at the bottom of the sea was a desolate one inhabited by rare monsters, completely dependent on nutrients from above.

The discovery of dense communities of tubeworms, crabs, snails, mussles, clams, shrimp and even fishes at these vents in concentrations that rivaled the rain forests meant that there had to be a totally new class of producer forming the basis of these bizarre ecosystems. There simply couldn’t be enough organic matter drifting down from above to support them otherwise. A fundamentally new type of energy pyramid had to be understood! The organism forming the basis of that pyramid had to be using a source of energy other than the sun to create sugars that in turn provided energy for the rest of the animals that otherwise would never be able to exist in such high numbers. It turned out that geology was the key. These perplexing organisms were tapping into energy from inside the earth, rather than 93 million miles away from it, in a process that remained undiscovered for the first 10,000 years of human civilization.

Stay tuned for Part 3: Hydrothermal Vents 101