Stories of the Sea - Bacteria, Water from Space, and the Origin of Life on Earth
By Safina Center Historical Journalism Fellow Raffi Khatchadourian
A Parapagurus sp. crab with a coral in the genus Epizoanthus on its back makes its way across a spectacular and unexpectedly densely packed field of ferromanganese nodules blanketing the seafloor of Gosnold Seamount, explored during Dive 16 of the 2021 North Atlantic Stepping Stones expedition. Image and caption courtesy of NOAA Ocean Exploration, 2021 North Atlantic Stepping Stones: New England and Corner Rise Seamounts.
Let’s start small. Veronique Greenwood has a fascinating story in Quanta Magazine about ocean microbes—specifically, prochlorococcus bacteria, “so small that you’d have to line up around a thousand of them to match the thickness of a human thumbnail.” Although tiny, they are unimaginably numerous: it’s thought there are three octillion of them. And they’re very busy. Using photosynthesis, they generate up to a fifth of Earth’s oxygen.
TEM image of “Prochlorococcus marinus,” a globally significant marine cyanobacterium. Photo by Luke Thompson from Chisholm Lab and Nikki Watson from Whitehead, MIT.
You might imagine them floating in the ocean as swarms of independent single-cells, but new research indicates that this is not quite the case. They often link up using pedicles called “nanotubes,” forming webs of ten or more, and sometimes link up with another bacterium, Synechococcus. As Greenwood puts it, their interiors join into a structure resembling multicellular life—becoming “more like rooms in a house than detached dwellings.” How exactly the bacteria form these odd constellations amid the wild ocean churn, and what exactly they are sharing, is not clear. But the revelation is a reminder that microbes, arguably the dominant life form on Earth—vastly more numerous, vastly heavier (collectively), vastly older, vastly more pervasive than humanity—remains so little understood. The finding made me recall something that Slava Epstein, a microbiologist at Northeastern University, said in profile that I wrote of him for The New Yorker years ago:
“A remarkable thing about microbes—and it is only remarkable from our anthropocentric point of view—is the coöperation among them,” he told me. “We in the macroscopic world need organic material as food, and oxygen to oxidize it, to get energy. You, a cow, a giraffe—we’re all the same. We may not be in each other’s way if one eats fish and the other grass, but little coöperation is possible, considering our metabolic needs.” Bacterial metabolism, on the other hand, is staggeringly diverse: some microbes eat ammonium, some eat hydrogen; some breathe sulfates, some breathe iron. Often, microbes are interdependent: what is waste for one is essential for another. “At some point, it becomes almost philosophical,” he said. “Perhaps the coöperation that evolved for four billion years in the microbial world has not evolved in the macroscopic world because it is younger. Maybe in two billion years we will find it to the same degree.”
Ocean-borne cyanobacteria, like plants, serve as engines of atmospheric oxygen, shaping and sustaining our world, but they may not be alone. Last year, researchers studying the Pacific Ocean’s abyssal sea floor published a paper in Nature Geoscience arguing that they had discovered another source of oxygen—or, as they called it, “dark oxygen,” because they found it in the lightless deep, produced by a chemical process that does not involve photosynthesis. Such a finding, Science noted, might well be a “monumental discovery,” potentially affecting our understanding life’s genesis—that is, if it proves to be true.
The researchers, lead by Andrew Sweetman, an ecologist at the Scottish Association for Marine Science, were examining polymetallic nodules: small, dark rocks containing metals of intense economic interest—nickel, manganese, copper, cobalt, iron, molybdenum—that are clustered like blackened scree across parts of the Clarion-Clipperton Zone seabed, spanning three thousand miles in the Pacific, at depths exceeding twelve-thousand feet. Although the nodules are not yet harvested commercially, several mining firms have been jockeying to do so, among them The Metals Company, based in Canada, which has negotiated an agreement with Nauru to help it gain access to a large part of the zone’s seabed, and with it the world’s largest nickel deposits, estimated at nearly five million tons.
Sweetman had extensive experience in the region; during his work there he and his team began to notice that samples from the sea floor around the nodules occasionally contained bursts of oxygen that were above background levels in the water—the precise opposite of what one would expect in the deep, where oxygen is typically consumed by living things. As he later recalled, “Over the course of ten years these strange oxygen readings kept showing up.” At first, his team thought that they were the result of a technical error. But then one day Sweetman was at a hotel bar in São Paulo, Brazil watching a documentary in which someone picked up a rock and described it as a naturally forming battery. Immediately, the mineral-rich nodules on the abyssal floor came to mind, and he wondered whether they were generating enough voltage to split oxygen atoms from water molecules—as he told CNN, “I suddenly thought, could it be electrochemical? These things they want to mine to make batteries, could they actually be batteries themselves?”
Manganese nodules in the Clarion-Clipperton Zone. ©ROV KIEL 6000, GEOMAR (CC BY 4.0)
To test the idea, his team sent down a device called a lander, equipped with multiple chambers, and drove it into the sediment to take controlled measurements of the water around the nodules. After some setbacks, the team detected a burst of oxygen. As Paul Voosen from Science reported, “They didn’t believe the oxygen was created or captured by the lander on descent. Microbial production couldn’t be completely ruled out, but that seemed unlikely when they saw oxygen rise even after adding poison to a sample.” After considering several explanations, they returned to Sweetman’s suspicion that the nodules might be “geo-batteries” and oxygen “may have partly resulted from seawater electrolysis.”
Sweetman’s language in the paper was tentative—posing the findings as support for a hypothesis, rather than a conclusion—but discussing his work with CNN he spoke with greater assurance, calling the discovery “profound and huge.“ The director of the Scottish Association for Marine Science, Nicholas Owens, went further, heralding the paper “one of the most exciting findings in ocean science in recent times.” He added, “The conventional view is that oxygen was first produced around three billion years ago by ancient microbes called cyanobacteria and there was a gradual development of complex life thereafter. The potential that there was an alternative source requires us to have a radical rethink.”
A rethink in academic terms, perhaps, but also one with real-world implications. The strange deep-sea nodules were already at the center of scientific and environmental controversy. Firms like The Metals Company have argued that the ores in them are a necessity, to build batteries that will help civilization transition from fossil fuels, and therefore avoid the worst consequences of climate change—an argument that critics, fearing the disruption a largely pristine landscape, have questioned. (John Oliver devoted an episode of his HBO show to the issue.) The nodules sit gently on the seabed, and so explosives would not be needed to get at them, but they nonetheless would have to be vacuumed up by large mechanical harvesters that would create plumes of sediment that could be highly disruptive, potentially affecting thousands of species that live on or around the nodules (which offer some of the only firm surfaces to attach to in the squishy deep-sea landscape). One study suggests the ecosystem might never recover from their removal.
The “dark oxygen” discovery—implying that the nodules may worth protecting not merely for ecological reasons but also because they could be key to the story of all life—entered the mining controversy as the latest flash point, then became a point of controversy itself. Researchers affiliated with The Metals Company and other mining concerns quickly challenged it. (The Metals Company had partly funded Sweetman’s research, and its scientists noted in their critique that they had accessed non-disclosed aspects of his data.) Sweetman, for his part, is planning another cruise, to build upon his paper—as he told Science, “Can you imagine how radical the idea is to propose that oxygen can be produced without sunlight? Do you think we wanted to propose something so outrageous?”
It is often claimed that humanity has mapped the universe more extensively than it has Earth’s oceans. Several new studies offer evidence that our oceans may well be an artifact of space: water transported here, in the form of ice, by comets or asteroids that smashed into Earth millions of years ago. One of the more intriguing papers on this topic came out in December, published by a team at NASA who discovered water on a comet called 67P/Churyumov–Gerasimenko that has a molecular signature resembling that of Earth’s water. The study follows a paper in July, by a different team, whose findings suggest that there may be more “dark comets”—objects combining aspects of both asteroids and comets—in our solar system than thought, offering, as one of the authors noted, “another pathway to get ice from somewhere in the rest of the solar system to the Earth’s environment.”
Just how much water might there be in space? A lot. Last year, astronomers found huge amounts of vapor surrounding a quasar, called APM 08279+5255, twelve billion light years from Earth—supporting the theory that water is not just common throughout the universe, but that it was prevalent very early on. The volume of water near that one quasar alone is staggering: about 140 trillion times the amount that is in all our oceans combined.