Dark Oxygen: A new challenge for our understanding of where and how life can emerge

In a groundbreaking discovery that challenges our understanding of life’s fundamental processes, Prof. Andrew Sweetman and his team have uncovered a novel electrochemical mechanism generating oxygen in the depths of the ocean. While the majority (70 %) of Earth's microbial life thrives without oxygen, relying on processes like fermentation, denitrification, sulfate reduction and methanogenesis, the 30% that depend on oxygen-rich environments are the focus of this revelation. Sweetman's discovery of "Dark Oxygen" production at the seafloor introduces a previously unknown source of oxygen, potentially reshaping our views on how life can emerge and persist both on Earth and potentially other planets. This newfound process not only impacts our ecological perspectives but also raises significant environmental concerns regarding the mining of polymetallic nodules, urging a reconsideration of current practices to protect deep-sea ecosystems. (1)

The importance of Oxygen in fundamental biological processes

Maybe you remember some of the biology from school or university where you’ve been taught about cellular respiration. Oxygens main function is to break down any glucose to produce ATP (adonesine triphosphate), which can be described as the energy currency of cells. Compared to anaerobic respiration, which can yield about 2 ATP molecules per glucose, the aerobic respiration allows for up to 36 – 38 ATP molecules per glucose molecule. Without oxygen the electron transport chain would basically halt and drastically reduce a cell’s ability to produce energy efficiently. Oxygen is also involved in the metabolism of carbohydrates, fats and proteins by breaking them down into usable energy, helping oxygen-dependent enzymes metabolize drugs and toxins to excreted more easily via your liver and countering invading pathogens by activating phagocytes, where reactive oxygen species (ROS) are produced, to increase your ability to fight off infections of any kind. (2)

In a more general sense oxygen plays a crucial role in various biogeochemical cycles, including the carbon and nitrogen cycle and is involved in the breakdown of organic matter and recycling nutrients to sustain ecosystems and support biodiversity.

So for all we know oxygen is a key ingredient to sentient life and it’s highly unlikely that a hypothesis brought forward by certain “shower thoughts” on Reddit such as the Exorphin theory claiming that plants actually evolved to be eaten by us, so that we would compost to be fertilizers for them, have any credibility to be true. And while thoughts such as “Oxygen is a drug that slowly kills us over 85 years” are inherently and biologically true, they clearly oversimply life in all its forms. (3, 4)

Discovering forms of Oxygen

We are mostly familiar with Oxygen in three forms:

As “O”, standing on its own with the atomic number 8 in the periodic table. It’s a highly reactive non-metal and it’s gaseous at room temperature. It’s colorless, odorless and tasteless in this form and a key ingredient in water (H₂O), which consists of two hydrogen and one oxygen molecule.
As “O₂” or dioxygen, where it is the most stable since two oxygen atoms are bonded together. It’s mostly known for its composition as CO₂ whereas C stands for Carbon. CO₂ is one of the most significant greenhouse gases.
As “O₃” or ozone. In this form it’s less stable, but acts as a protective layer in earth’s stratosphere, absorbing around 95 % of UVA / B radiation and therefore protecting all living organisms under the sun from its harmful and highly damaging effects. (5)

By At09kg, Wattcle, NefronusAt09kg: originalWattcle: vector graphicsNefronus: redoing the vector graphics - This file was derived from: Photosynthesis.gif:, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=49183032

Discovering the origins of Oxygen

The largest known contributor to oxygen production is by far photosynthesis. Hereby plants, algae and cyanobacteria produce the vast majority of earths oxygen by absorbing light energy to split water molecules (H₂O) into breathable oxygen (O₂), protons (H⁺) and electrons (e^-) whereby oxygen is released as a byproduct. Just marine phytoplankton alone is estimated to contribute about 50 – 85 % of all oxygen. Especially in the early history of earth cyanobacteria played a crucial role in oxygen production leading to what is called the “great oxygenation event” approximately 2.4 billion years ago, setting of a whole chain of events in motion leading up to the Cambrian explosion of life.

All other forms of “oxygen production”, such as photolysis, where UV light breaks down water molecules in the upper atmosphere, lightning where water vapor dissociates into hydrogen and oxygen, or even volcanic degassing or water radiolysis play only a very small role compared to photosynthesis.

Note, that not all oxygen is distributed evenly. Especially the deep sea with little currents is often short in oxygen and sometimes void of life as a result of it. Oxygen slowly trickles down through water with currents providing minimum surviving conditions for animals and plants. And this is where a new kid has shown up on the block, Dark Oxygen. (6, 7, 8)

One of our benthic chambers on the seafloor as part of the MiningImpact2 project. (© ROV team/GEOMAR) - https://mpi-bremen.de/en/Benthic-Chambers.html

Discovering Dark Oxygen and its meaning for local oxygen generation

In 2013 Andrew Sweetman set out to measure the consumption of oxygen at the seafloor using a benthic chamber. “Benthos”, which is greek for “depths of the sea” refers to a device that is stuck in the ground to isolate a specific area of the seafloor. Normally you’d see oxygen levels slowly go down overtime, because it’s being consumed by microbes and bacteria in the chamber. But what happened during Sweetmans experiment was that the oxygen actually increased. Fumbled by these results he assumed for about 8 years that he was working with faulty sensors. It was only in 2021 when he did another expedition using two different sensors this time, yielding still the same results, that he new something must be going on here.

He conducted his research in the Clarion-Clipperton Zone somewhere between Hawaii and Mexico at a depth of around 4000 meters. This region in the central pacific is a breaking point in the oceanic crust and of high interest by many states and governments for its high yield of polymetallic nodules. These are basically small stones commonly rich in Nickel, Cobald and Mangan (also known as manganese nodules) which can grow a new 1 – 10 mm layer of rare earths in about one million years and they are just laying around on the seafloor ready to be mined and help fuel our new green-economy.

Sweetman found that these stones were the reason for the increase in oxygen when he encapsulated them in his benthic chambers. So he took some samples to test his hypothesis in the lab. He started probing the surface of the nodules to look for voltages that could be detected which would explain the oxygenation of the surrounding area and amazingly they found voltages up to almost 1 V. This extraordinary finding of a naturally occurring process is similar to what happens when you drop a battery in seawater, it starts fizzing because the electric current that starts is splitting water into oxygen and hydrogen. For mostly dramatic reasons the process was named DOP or dark oxygen production, because it happens at the floor of the sea without any light being involved and dark stones being the culprit. (1, 9)

Polymetallic nodules on the seafloor – snapshot taken from this video https://www.youtube.com/watch?v=uP3RPDTgfa4&t=55s

This provides a new perspective on the industry of mining these nodules, because whatever quantities of oxygen is produced (that is for a future mission to find out), is likely consumed very locally and its absence could contribute to the extinction of an unknown amount of species if not being done carefully.

Additionally, this research brings us back to the drawing board of the conditions under which our own planet has evolved life on and below its surface. There was maybe another source of oxygen for life that breaths it and it could have persisted even before photosynthesis.

Even when looking to the stars we must now also include this newly discovered process when calculating the probabilities for complex and oxygen dependent life on other planets.

All the while, mining companies are working to dismantle the science behind it to downplay the importance of these new findings and to be able to continue extracting the high-worth polymetallic nodules. Unfortunately, further research has already shown that ecosystems don’t recover after extraction has taken place, so be ready for a new environmental battle. (10)

by mario