“Somewhere, something incredible is waiting to be known.”
― Carl Sagan
It was a few minutes before midnight, February 15th 1977, when an abnormal temperature spike was recorded along the oceanic depths of the Galapagos Rift. A group of explorers slowly descended into the black abyss to investigate. Brilliant flashes would momentarily zip past the viewport of their state-of-the-art research submersible. Flashes that, unmistakably could only have belonged to beguiling bioluminescent organisms, giving a glorious underwater light show. But whatever light (along with life) there was, it began to diminish.
The explorers were now well over 8,000 feet below the ocean surface, eager to explore, but blind to this new and dark alien world previously discovered by none. The remotely-operated sensors on board the submersible began to pick up temperature spikes on the freezing sea floor.
They had found the anomaly.
They were on the search for deep-sea hydrothermal vents. And as expected, there it was. And there they were… Little did these explorers know, that this single ‘anomalous’ temperature spike would unlock perhaps the most ancient story of life, forever changing the way we think about life here on Earth, on other planets, and its possible origins.
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The explorers in the submersible (named Alvin) were a three-man crew: Jack Donnelly as pilot, and Jack Corliss and Tjeerd van Andel as the scientific observers.
‘Isn’t the deep ocean supposed to be like a desert?’ asked Corliss to his graduate student, Debra Stakes, on the surface.
‘Yes…’ answered Stakes, perplexed.
‘Well, there’s all these animals down here.’
Giant white clams the size of dinner plates, strange orange animals shaped like dandelions, crustaceans with teeth on their eyestalks, never-before-seen mussels, pink fish and purple octopuses, shrimps, anemones, snails, lobsters, whelks, limpets… And to top it off, giant six-foot-long tubeworms, mouthless and anus-less, connected to the hydrothermal vents themselves.
If finding a fully functional ecosystem over 8,000 feet below the ocean surface – at a pressure that would crush most life on land – and towering volcanically-driven vents pumping at temperatures up to 350°C sounds like science-fiction to you, then I can assure you, it is not.
Hydrothermal vents are borne out of violent underwater volcanic activity, two opposing and contradictory forces colliding to form colossal chimney-like towers rivalling that of skyscrapers. Superheated fluids below the ocean’s crust – so hot they strip out the metal atoms from nearby rocks – rush towards the surface and hit the near-freezing seawater, forming an entirely new solution that rapidly solidifies to form these hydrothermal vents – otherwise known as “black smokers”. But how did life find a way to thrive in this seemingly inhospitable environment completely devoid of sunlight?
The secret lies in the smoke.
Actually it’s not even smoke. The vent fluids are filled with dark metal particles, or more specifically, scorching hydrogen sulphide, giving the illusion of smoke.
Most life cannot survive within these superheated black smokers, let alone in the presence of hydrogen sulphide – which is highly toxic to most animals, comparable to carbon monoxide (apparently, it gives off a very nauseating odour – although luckily, it deadens your sense of smell before killing you).
But some microbes are able to survive just outside the black smokers. One example is the sulphur bacteria. Existing between the temperature gradients, these bacteria feed off the hydrogen sulphide. They extract the hydrogen and attach it to carbon dioxide to form simple nutritious organic matter. Vent animals graze on the sulphur bacteria, forming a neat food chain. The giant tubeworms having no gut, mouth or anus harbour the bacteria inside of them – a symbiotic relationship (one of life’s many relationship goals) – to obtain the essential sugars and amino acids. The red-tipped “feathers” found at the crown of these tubeworms contain complex haemoglobins (giving these “feathers” their bright red colour, just like in our red blood cells) that bind to hydrogen sulphide before being transported as food for the bacterial farm within*.
* I’m going off on a tangent here, but what is remarkable about these haemoglobins is that they are able to carry oxygen in the presence of sulphides – something most other animals are unable to do. Although my understanding of this process may be limited, perhaps this knowledge could be used to develop an antidote for sulphur dioxide poisoning. Note: there is currently no antidote for sulphur dioxide poisoning. Now let's get back to the article!
12 H2S + 6 CO2 → C6H12O6 + 6 H2O + 12 S
There it is. This single equation portrays the innovative chemical reaction taking place simultaneously inside billions of tiny sulphur bacteria, in turn allowing a community of animals with a biomass rivalling that of a tropical rainforest to survive and thrive on the seafloor. It is this equation that powers much of the vent world without any direct input from the sun.
I’ll show you the single equation that powers much of our world, the world above the ocean and on land:
6 H2O + 6 CO2 + sunlight energy → C6H12O6 + 6 O2
Beautifully familiar, isn’t it? You might have heard of this process, it’s called photosynthesis. Prior to the discovery of hydrothermal vents, the scientific consensus was that all life on Earth was powered by photosynthesis – in other words, light from the sun. It was thought that maybe microbes (or small animals at the very most) that lived at the bottom of the ocean survived on sunken dead plants or animals, even carcasses of dead whales… In other words, surviving, but still completely reliant upon sunlight.
But upon the discovery of hydrothermal vents, this theory was completely turned on its head; in fact, it couldn’t have been further from the truth. Not only did animals exist – they grew rapidly and to giant sizes. These explorers had just found an entirely new form of life: chemosynthesisers – which, rather than harness energy coming down from the sun, draws upon the energy coming from within the Earth.
It’s both extraordinary and terrifying to think that this discovery rested on a single, anomalous temperature spike. Since then, our perception of life has been impacted, deeply. What other strange worlds exist on our planet? Could there be life below the sea floor—or on other planets, or even other objects beyond Earth? One particular area that has been heavily shaped and influenced by this discovery is the origin of life.
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The discovery of hydrothermal vents together with its thriving vent community deeply impacted our perception on the origin of life, giving rise to a theory that attempts to address how molecules become microbes, how chemistry becomes biology: this is the alkaline vent theory.
Unlike the vents described above, alkaline vents are not volcanic but instead rely on the reaction between seawater and freshly exposed rocks. These rocks physically incorporate water molecules into their structure, eventually causing it to expand and fracture, allowing even more seawater to be incorporated.
Eventually these super-hydrated rocks descend beneath a colliding plate on the sea floor, where they fall victim to the searing heat of the Earth’s mantle and ultimately release all their water back into the ocean in the form of gases, particularly hydrogen gas. Various other gases (similar to those used in the Miller-Urey experiment**) also precipitate out of the vent and into the cool acidic ocean water to form towering, porous rocks: the alkaline vents. The release of hydrogen provides a redox gradient, the thermodynamic disequilibrium necessary to power the conversion of carbon dioxide (from restless volcanoes) to methane, ammonia and hydrogen sulphide – the essential molecules of life.
**Another quick point to raise: the Miller-Urey experiment (conducted in 1953) was a pioneering chemical experiment that aimed to simulate the conditions of the early Earth. Its purpose was to find out how life may have arisen through simple chemical reactions. In the end, the two scientists found that these early conditions were able to give rise to amino acids – molecular precursors to life. Although this gave scientists brilliant insights into pre-biotic chemistry, the experiment relied on highly improbable chemical events (primordial soup theory) which still does not shed any light on how these molecules obtain the energy to grow and evolve to greater complexity – a quality that would at least have some semblance to the complex life we see today.
But it doesn’t end there. Curiously enough, tiny compartments were found in fossilised deposits of these alkaline vents. A geologist who goes by the name of Mike Russell examined one such fossil, around 350 million years old. He noticed that these microcompartments were eerily similar in size to organic cells, and even more impressive was the fact that they appeared to be interconnected, forming a complex network across the rock. Could these have been the first proto-type cells? These microcompartments addressed an issue that most origin-of-life experiments ignored: concentration.
With walls composed of catalytic iron-sulphur minerals, these micro-compartments provided an ideal environment for organic molecules to become concentrated within – exploiting the proton gradient within the ocean waters. The organic products of these reactions could then interact with each other to form even more complex carbon-containing molecules, before forming an early type of RNA. This is a bold theory, and along with it are Russell’s visionary words, published in a 1994 paper:
“We propose that life emerged from growing aggregates of iron sulphide bubbles containing alkaline and highly reduced hydrothermal solution. These bubbles were inflated hydrostatically at sulphidic submarine hot springs sited some distance from the oceanic spreading centres 4 billion years ago.”
Extending this theory, some of the early RNA-based cells could have escaped the nurturing confines of the porous rocks to become free-living – albeit, still relatively close to the vents. Here, the proto-cells could still rely on the vent’s naturally generated proton gradients. But what if they were to become independent of the vents? The membranes of these proto-cells would need to have their own protein pumps, independently generating and sustaining their own ion gradient – since, without an ion gradient there is no power.
One solution would be for the cell to develop a simple sodium-proton pump – a protein that is able to create sodium gradients by pumping sodium ions out of the cell for every proton pumped in. This revolutionary idea, elucidated by Nick Lane and William F. Martin is one of the leading theories on the possible origins of life as we know it. However, it is also important to note that there are many other brilliant theories out there, which, for brevity I cannot explain in one article, but that nevertheless deserve equal consideration and contemplation.
The discovery of hydrothermal vents didn’t just shed light on plausible hypotheses for the origin of life, it also illuminated the powerful yet compelling idea of life not as we know it. Perhaps this universe is far too vast to only be playing by the rules of life we are familiar with here on Earth. Not bad for a seemingly anomalous temperature spike.
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This article is the original full version of the article published in The Fold, which was abridged to meet the length requirements of the newsletter. This article is Part 1 of a three-part series, exploring the elements of biochemistry we don’t talk about enough! In the next article we will continue on with the impact of hydrothermal vents and explore possible extra-terrestrial biochemistry, future missions in the search for life beyond Earth, and the importance of going beyond an Earth-centric perception of life. A special thanks to Professor Ian Crawford for giving the talk, Science behind the Martian, which partly inspired this series, and a special thanks to the UCL Biochemistry Society for organising it.
