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Want to know what alien waters could be like? Go to the bottom of the ocean
Some of the most alien worlds that we know of are right here in the eldritch depths of our planet's oceans.
Imagine an oasis on the seafloor, where plumes of magma-heated water gush from the bowels of the Earth and make it possible for life to thrive in an otherwise freezing watery wasteland. These forms of life even look alien. From tube worms that resemble giant lipsticks to thick bacterial mats and ghostly crabs, things can obviously survive wherever there is a hydrothermal vent, but not all vents are the same. Where is life most likely to spawn?
This is what biogeoscientists Jeffrey Dick and Everett Shock wanted to find out when they did a deep dive into what conditions make it most likely for some really bizarre organisms to stay alive around these vents, which provide heat and food in otherwise inhospitable places. They recently published their findings in Journal of Geophysical Research: Biogeosciences. Turns out that life on the surface takes in energy — but life in the depths releases it.
“Our food has reduced organic molecules, and in the presence of oxygen they tend to be oxidized to CO2,” Dick told SYFY WIRE. “Near a hydrothermal vent, CO2 is unstable in the presence of hydrogen from vent fluids, and tends to be reduced to organic molecules.”
There are reduced carbon molecules in just about everything we eat — obviously, because most of those things were once alive. Even potato chips were once potatoes. Those potatoes were carbon-based life forms, and anything made of molecules with a carbon-hydrogen bond is an organic substance. When exposed to oxygen, the carbon molecules in our food are oxidized to CO2. It makes them unstable. Our cells benefit from this reaction by capturing the energy released and using it to synthesize different necessary molecules such as polymers.
The opposite happens in the strange environment of a hydrothermal vent. Vent fluids are unstable, and so is the hydrogen in them, which is gradually reduced to organic molecules. This process happens extremely slowly because of that instability. It gives organisms around the vent a chance to take advantage of the reaction, accelerating it to keep themselves going, and more hydrogen means they can catalyze more energy. When these creepy crawlies create proteins (which are made of amino acids and polymers), they release energy instead of absorbing it.
“Amino acids have different elemental compositions and therefore a different oxidation state of carbon,” said Dick. “Amino acids with more hydrogen atoms in the side chain are more reduced, while those with more oxygen atoms are more oxidized. Energy for protein synthesis depends on oxidation state.”
To get an idea of optimal vent conditions for life, Dick and Shock used the entire genome of the known denizen of these environments, the methanogen (an organism that produces methane) Methanocaldococcus jannaschii. For the hypothetical part meant to help them figure out what breathes life into the bottom of the ocean, they used group additivity to model hypothetical proteins. Group additivity is a model that predicts the heat it takes for organic molecules to form. It includes the amino acids in proteins and the energy needed for polymerization.
For life to have a chance at thriving, it should be around a vent made of volcanic rocks that are rich in hydrogen, with temperatures around 185 degrees Fahrenheit. That hydrogen is needed for organisms to power themselves. To synthesize proteins, which are made of amino acids, these cells depend on carbon that is oxidized to a certain level, because as the experiment proved, proteins have to be reduced or oxidized. This could possibly be happening somewhere out in space. Dick isn’t ruling out the possibility of vent life on a water world such as Europa.
“I think the lesson from our study is that building large organic molecules is not necessarily energetically prohibitive,” he said. “It depends very much on the geochemical conditions, and that's a reason for doing more exploration and modeling of other worlds.”