Figure 1: The Great Oxygenation Event: the natural history, over time, of atmospheric gases.

      A single question remained for a long time, however: Where had all this oxygen come from? Something substantial must have happened for a whole new gas to transform the planet in such a unique way. The story of how we began to understand where oxygen came from, and how it changed the world, is an extraordinary tale of hard work, keen observation, and luck (a combination that likely describes many, if not most, scientific discoveries). It’s also a story that simply is not well known—but should be.

John Waterbury grew up in the Hudson Valley of New York but spent his summers in the coastal Cape Cod town of Wellfleet, Massachusetts. There, in the early 1960s, Waterbury wandered around the expanse of dunes that stretched into long beaches and looked out into the blue-green ocean water of the Atlantic. Not satisfied to remain on the shore, he took to the ocean in his Lightning dinghy racer. Surrounded by salt water and rolling waves, he was filled with a sense of wonder as his boat glided over the waters off Cape Cod.19

Waterbury’s first academic stop was at the University of Vermont, where he earned a degree in zoology in 1965. After graduation, his options were narrowed down to two. There was a research position at the Woods Hole Oceanographic Institution in Massachusetts, a mere forty miles up the Cape from his Wellfleet summer home. If he didn’t stay in academics, the draft awaited him, with a possible tour of duty in Vietnam. Not surprisingly, Waterbury chose Woods Hole. He spent four years there, studying nitrifying bacteria, little organisms that digest nitrogen-containing matter. Afterward, he enrolled in a doctoral program at the University of California, Berkeley, and spent a few years in Paris. He returned to the Oceanographic Institution in Woods Hole in 1975, this time to stay. At Woods Hole, Waterbury discovered how Earth had changed from a planet without oxygen, inhabited only by microscopic organisms, to one with oxygen, teeming with all sizes of life.20

      During his doctoral studies at Berkeley, Waterbury found his passion in cyanobacteria, microorganisms that were known to colonize fresh water. More commonly known as blue-green algae, these organisms have properties more like those of plants than of bacteria. Foremost among these unusual properties is the ability to photosynthesize—to turn carbon dioxide and water into oxygen and carbohydrates. But in the 1970s, cyanobacteria were mostly known to colonize only small freshwater areas and were thought to have had a limited role in the Earth’s process of oxygen production. They were not talked about outside of a small academic circle, and no mention of them appeared in major oceanography textbooks.

      After his doctoral studies, Waterbury settled into his job as a research scientist at the Oceanographic Institution. A primary mission in the field at the time was to study ocean bacteria, of which not much was known. Field trips were a regular part of the investigation, and in August 1977 Waterbury headed out on the research vessel Atlantis II to the Arabian Sea, the mass of ocean between India and Saudi Arabia known for having very high levels of inorganic nutrients and a rich marine life. His team’s mission was to analyze samples from the ocean using a new technology: epifluorescence microscopy. The goal was to establish typical levels of known bacteria in the ocean with this new technique.

      The basics of epifluorescence microscopy are straightforward. Tags, made up of the building blocks of DNA, are added to a sample of water, where they attach themselves to corresponding parts of the DNA of bacteria, like puzzle pieces fitting together. Under the blue light of the microscope, these bacteria then fluoresce green from their newly attached tags. If no matching bacteria are present, the tags won’t be activated, and the view in the microscope will remain blank.

      Before adding his DNA tags to the Arabian Sea water, Waterbury did one thing that all students are taught in science class, a mandatory step for every experiment at every level of science, from middle school classrooms to Nobel Prize–winning labs: he set up a rigorous control to ensure his results would be valid. Scientists know that controls are the backbone of all discovery. To find something abnormal, one needs to be able to see, and prove, the existence of what one thinks is normal. So, prior to adding the DNA tags, Waterbury analyzed an unaltered specimen of water from the Arabian Sea under the new epifluorescence microscope so that he would have a baseline for comparison.

      Waterbury assumed he would see nothing unusual in the Arabian Sea water, but instead he was stunned. The blue light of the epifluorescence microscope went through the water, and a bright-orange fluorescence came shooting back out of the eyepiece. Because of his background in cyanobacteria, Waterbury recognized the orange light as the natural fluorescence of phycoerythrin, a photosynthetic pigment that works with chlorophyll to drive the all-important carbon-dioxide-to-oxygen-and-carbon reaction, making life on this planet possible. Cyanobacteria had never been reported to exist in deep-sea salt water, so this was a monumental new finding.

      The initial discovery of cyanobacteria in the Arabian Sea was an introduction, but in order to be able to study saltwater cyanobacteria in depth, Waterbury knew he would have to grow them in culture. He tried for months, each time using a new medium and different nutrition to coax the cyanobacteria to replicate. But each time the same thing happened—within twenty-four hours the cells were all dead. Culturing these bacteria was a must if the study of saltwater cyanobacteria was going to advance. In order to succeed, Waterbury had to go back to basic environmental biology.

      Ocean organisms and freshwater organisms behave very differently. Normally we think of ocean creatures as hardy and adaptable, and the ocean as a rough and wild place. Freshwater bodies, by comparison, seem quiet and tranquil, without sharks and stingrays and deadly jelly­fish. This is the human perspective. From the perspective of bacteria, the reverse is true.

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