The deep ocean floor is covered in naturally-occurring batteries that make oxygen... Wait, WHAT?!

This has HUGE implications for life on icy moons. Interesting New Paper #3...

A truly extraordinary paper has just been published in Nature Geoscience: “Evidence of dark oxygen production at the abyssal seafloor,” by those doughty warriors for truth (…deep breath… people who put all that work in deserve to have their names mentioned when that work is being discussed… OK, here we go…) Andrew K. Sweetman, Alycia J. Smith, Danielle S. W. de Jonge, Tobias Hahn, Peter Schroedl, Michael Silverstein, Claire Andrade, R. Lawrence Edwards, Alastair J. M. Lough, Clare Woulds, William B. Homoky, Andrea Koschinsky, Sebastian Fuchs, Thomas Kuhn, Franz Geiger & Jeffrey J. Marlow. Phew!

It’s all about polymetallic nodules, so I’d better explain what they are first.

BALLS!

This brooding hunk is a polymetallic nodule. The slightly lengthy but legally important CREDIT: By User Koelle on de.wikipedia - Koelle, selbst fotografiert, own photo, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1345805. Thank you, User Koelle, for letting me use your lovely photo.

Polymetallic nodules are found on the deep seafloor here on Earth, and look like roundish, roughish rocks. Basically, balls. They range in size from too-small-to-see, through a small pea, to a large potato. They form slowly and naturally (the process can take millions of years), through straightforward, mostly non-biological, chemical processes, layer by layer. The various layers are formed from different metals – mostly manganese and iron, but also cobalt, nickel, sodium – so if you cut one open, it would look like a metal version of a gobstopper.  And they cover millions of square kilometres of sea floor. You can find up to 15 kilograms of these nodules per square meter.

This new paper outlines how some of those polymetallic nodules, a couple of miles beneath the waves, out in the middle of the Pacific, seem to be producing oxygen.  This was, to put it mildly, not anticipated. This was so not anticipated, in fact, that the team of scientists kept sending the sensors back to the manufacturers, because mainstream theories have always assumed oxygen could not be produced several miles down, as there's no sunlight to allow for photosynthesis. And photosynthesis (by plants and algae) is how all our oxygen is usually produced, whether on land, or in the shallow surface waters of the seas, where sunlight penetrates.

“I basically told my students, just put the sensors back in the box. We’ll ship them back to the manufacturer and get them tested because they’re just giving us gibberish. And every single time the manufacturer came back: ‘They’re working. They’re calibrated.’”

– Andrew Sweetman, head of the seafloor ecology and biogeochemistry research group at the Scottish Association for Marine Science, on CNN

So, this really is an astounding discovery.  The production of oxygen by these manganese and iron and cobalt and nickel nodules seems to be, as far as we can tell so far, the result of a purely chemical reaction.  But that purely chemical oxygen production is enabling biological life at these extreme oceanic depths.

Here’s a link to a good report from Science Daily.

And here are the juciest quotes…

"The polymetallic nodules that produce this oxygen contain metals such as cobalt, nickel, copper, lithium and manganese -- which are all critical elements used in batteries," said [Franz] Geiger, who co-authored the study. Geiger is the Charles E. and Emma H. Morrison Professor of Chemistry at Northwestern's Weinberg College of Arts and Sciences and member of the International Institute for Nanotechnology and the Paula M. Trienens Institute for Energy and Sustainability

"When we first got this data, we thought the sensors were faulty because every study ever done in the deep sea has only seen oxygen being consumed rather than produced," [Andrew] Sweetman said. "We would come home and recalibrate the sensors, but, over the course of 10 years, these strange oxygen readings kept showing up.

"We decided to take a back-up method that worked differently to the optode sensors we were using. When both methods came back with the same result, we knew we were onto something ground-breaking and unthought-of."

To investigate this hypothesis, Sweetman shipped several pounds of the polymetallic nodules, which were collected from the ocean floor, to Geiger's laboratory at Northwestern. Sweetman also visited Northwestern last December, spending a week in Geiger's lab.

Just 1.5 volts -- the same voltage as a typical AA battery -- is enough to split seawater. Amazingly, the team recorded voltages of up to 0.95 volts on the surface of single nodules. And when multiple nodules clustered together, the voltage can be much more significant, just like when batteries are connected in a series.

"It appears that we discovered a natural 'geobattery,'" Geiger said. "These geobatteries are the basis for a possible explanation of the ocean's dark oxygen production."

–Science Daily. (Materials provided by Northwestern University. Original written by Amanda Morris.)

THE GEOSPHERE ENABLES THE BIOSPHERE

This is a beautiful example of something that we're going to see again and again, when we examine the totality of a planet like Earth, and treat it as an evolved system: the geosphere actively enables the biosphere. They are inextricably entwined. In particular, inorganic chemistry complexifies over time in such a way as to create the conditions for organic chemistry. Put more simply, rock chemistry generates the conditions for egg chemistry.

It’s all one integrated developmental path. And I think you're going to see this even more in the case of icy moons: deep under their frozen crust, in their liquid water oceans, the geosphere is going to enable the biosphere, in ways that will surprise those scientists who are not expecting a system fine-tuned (by evolution at the level of universes) for the production of life. 

We  often call the rainforests of the Amazon, the Congo, south-east Asia, etc, the lungs of the world, because they produce the oxygen that animals and birds and insects and popes and peasants and poets need to survive. Trees, which self-assemble by pulling carbon out of the air, provide that function on land.  Their roots take in water (H2O), while their leaves take in carbon dioxide (CO2), and use the energy from sunlight to crack the chemical bonds between the carbon and the oxygen. The carbon, hydrogen, and some oxygen get used to make glucose (C6H12O6), which feeds and grows the tree. There’s a lot of oxygen left over, and that is excreted. (6CO2 + 6H2O + dear old sunlight = C6H12O6, a delicious glucose molecule + 6O2, a lot of oxygen left over.) But now we have found purely chemical, non-biological, non-carbon based producers of oxygen, in the deepest depths of the oceans of Earth.

THE DEEP SEA HAS BATTERY-POWERED LUNGS

The deep sea has lungs.  They produce enough oxygen for life to flourish, and they do it without sunlight, in deep water, purely chemically. Sure, most of the oxygen down there still comes from biological activity miles above, dissolved into the shallow surface waters, and carried into the depths as it cools and falls. But hey, this new source is a radical discovery.

The implications for life in the liquid water oceans, under the surface of icy moons, are obvious, and enormous.  So I'm going to predict now, with medium confidence (and a couple of caveats, to follow) that we may well ultimately discover similar polymetallic nodules, producing oxygen through similar chemical processes, on the warm seafloors of the liquid water oceans under the frozen crusts of icy moons. 

The same sea floor volcanic vents that melt the ice to make those liquid water oceans will also provide the manganese, iron, cobalt, nickel, et cetera, that these nodules require. 

Obviously, this requires the icy moons to have rocky cores with a fairly high degree of manganese, iron, nickel, and cobalt content. (OK, maybe not much cobalt.)  I think this will turn out to be the case for a high percentage of icy moons.

As I'm arguing in a series of posts, I think liquid water oceans on icy moons will turn out to be the commonest homes for life in this universe.  And the biosphere in such oceans would have to be powered, not by sunlight, but by the gravitational energy of the planet tugging on the moon’s core, thus keeping it molten. Which is great, but… those liquid water oceans are under a mile or two of solid ice, incredibly far from the sun. Zero sunlight down there. No photosynthesis...

So polymetallic nodules could potentially solve the oxygen problem, performing the function photosynthetic plants do on Earth.

A CHANGE OF HAT

Okay, that was all written wearing my positively-charged optimist’s hat. Now let me put on my negatively-charged pessimist’s hat, and lay out some possible problems in transferring this finding to icy moons.

Quite a bit of research has been done into how these polymetallic nodules seem to form. And on Earth they need a decent amount of free oxygen to form in the first place – they are made by a redox (reduction and oxidation) reaction, and they are full of metal oxides (where the metal has combined with oxygen). Decaying biological life provides some of that oxygen. Oxygen from the surface, descending in cold water, provides some more of it. And that oxygen was provided by life – trees, algae, cyanobacteria, other phytoplankton, seaweeds... So, on our planet, in our era, those nodules can't build themselves until there is already free oxygen – and life –present. That's fine once there are a lot of nodules already there, generating electricity, cracking seawater, and making oxygen. But you can't use them as the original source of oxygen. Photosynthesis still performs that function.

But it’s still possible that nodules might form, in the absence of oxygen. (Remember, there’s almost no free oxygen in the air or sea before life takes off, because oxygen is so reactive it gets locked up immediately. Without a source to replenish it – a tree, algae – it all goes away, fast.)

The earliest nodules, in the absence of oxygen, wouldn’t make themselves out of layers of metallic oxides; they would instead combine with sulphur, to form metallic sulphides. That’s because sulphur is abundant in the early oceans, and is structurally similar to oxygen, thus forming similar bonds. Life on icy moons, like life on earth, will probably be sulphur-based before it transitions to (more efficient, but hard to unlock) oxygen.

My guess, then, is that these sulphide-rich nodules on icy moons will be part of an early sulphur-based ecosystem. But if those sulphide-rich nodules can crack seawater (though probably less efficiently than the later oxide-rich nodules), they can slowly help life make the switch to oxygen. The free oxygen they produce initially will not be available to make nodules (or feed new, improved oxygen-eating bacteria!) for a long time, as dissolved iron in the water will eat up any free oxygen immediately, to form iron oxide (rust). Something similar happened on earth, for a long, loooooong, time, as the earliest oxygen-making forms of life (probably cyanobacteria) simply fed their oxygen to the plentiful iron in the ocean. (It rained rust in every ocean on Earth for hundreds of millions of years: the resulting Banded Iron Formations – dark red sedimentary rocks – are hundreds of meters, even up to a kilometre, deep, all over the world). But when the iron levels in the oceans of the icy moons drop enough, the nodules will switch from a sulphide regime to an oxide regime, and to more efficient oxygen production. And life can transition, on those icy moons, to oxygen and away from sulphur, as it did on earth. There is a evolved chemical logic to life...

This is highly speculative, and I wouldn't bet my house on it (if I had a house), but I think we will see something like that. (Chemists, give me feedback!)

Meanwhile, the deep ocean floor on Earth has millions of square kilometres covered in a thick forest of naturally-produced batteries, quietly cracking seawater into hydrogen and oxygen, deep down where the sun don't shine. As I have said before, and I'll say again: it's always more complicated. There's always more orderly structure. (Rocks turn out to be batteries!) There's always more meaning.

This may inspire me to finish my two other posts on icy moons, which I have in my stack of unfinished posts. Fun times!

OK, I am off on holiday in the morning, camping for a week with my delightful family, and largely offline. (I’m finishing this while knackered, just before I go to bed, so excuse typos.) Hope you are having a good summer, and I will see you again soooooon...