Dark Oxygen: A New Origin of Life, Or A Dead End?

Breathe in. Breathe out. That’s the work of billions of years of oxygen production and evolution in the span of one second. Traditionally, the narrative of early life on Earth tells us that there wasn’t much oxygen in the early days until the Great Oxygenation Event around 2.46 billion years ago.  Cyanobacteria filled our oceans and atmosphere with oxygen derived from photosynthesis, allowing for a future where you can sit and comfortably read an article like this. However, this story may be about to change. 

This past July, deep in the abyssal depths of the Clarion-Clipperton zone (CCZ) in the Pacific Ocean, a team of researchers led by Prof. Alexander Sweetman of the Scottish Association for Marine Science observed something unique when performing enclosed experiments to measure oxygen consumption by organisms in sediments. These experiments were performed in situ, or on-site, and noted that oxygen levels increased in some of the experimental chambers, implying oxygen was being produced at a rate at least on par with what was being consumed by any organisms present.

Where was this oxygen coming from, and was it really there? It’s too early to know for sure. Sweetman’s team has proposed an explanation for the theory of ‘dark oxygen’, and it involves something less ominous than the name implies: polymetallic nodules. These nodules are currently a prospective target for deep-sea mining, as they contain a great deal of valuable material such as manganese, nickel, or rare earth elements. The potential economic value of these nodules aside, they also seemingly hold great ecological value to creatures living in the CCZ, as organisms have been found living on and around them — though our knowledge is certainly still lacking. 

The nodules were found to have a measurable electric charge, around 1V, according to Sweetman’s team. This charge, the team went on to propose, may allow them to split water via electrolysis (i.e. using electricity to drive a reaction) into hydrogen and oxygen. These nodules could therefore be even more vital to the deep-sea ecosystems they are a part of.  

Not only does the idea of dark oxygen raise questions about the ecological ethics of deep-sea mining, but it also begs the question of whether the origins of life can be found in metallic nodules in the sand. Further questions arise if you look up: if it could happen here, what about elsewhere? Exoplanets may be too far to reach just now, but moons in our solar system such as Titan or Europa have been pointed to as promising research targets for astrobiology. Could there be dark oxygen at work, providing for life we have yet to meet?

Dr Eva Stueeken of the University of St Andrews School of Earth and Environmental Sciences urges caution before getting too carried away in the potential ‘what-ifs’ of dark oxygen. In her opinion, “It would be better not to speculate too much about the broader implications of the study until somebody has successfully replicated it.” This caution is not unwarranted. Already, scepticism over Sweetman’s findings has begun to surface, both from fellow scientists and — interestingly — mining companies, such as the deep-sea mining Metals Company, which recently published a rebuttal to Sweetman’s team's findings, thoroughly rejecting them. 

The potential discovery of dark oxygen has therefore unlocked new avenues for much-needed research, discussion, and exploration, regardless of whether these nodules are actually making their own oxygen or not. This could take humanity's knowledge anywhere in space, to the farthest ends of time, or could leave us at an impasse; richer in knowledge but not in truths. 

Image by Elizabeth Lang