At the opening ceremonies of the 2004 Olympics, Björk, our most delightfully alien pop singer, sang her song “Oceania” while swaying her arms like an anemone. Representing the goddess Mother Ocean, she told the people of Earth, “Your sweat is salty / I am why.”

Stefan ­Helmreich, an MIT anthro­pology professor who had been working on his book Alien Ocean for a few years, watched with fascination. Björk, he says, was retelling an old and enduring story about the seas that persists even in the way marine microbiologists describe their work: “The ocean is the source of all life; it’s a life-giving fluid.”

Helmreich spent years doing fieldwork among these scientists, listening carefully as he sat next to people piloting deep-sea robots and gathered virus samples in the Sargasso Sea with researchers working for the renowned MIT microbiologist Penny Chisholm. Alien Ocean tells their stories and explores how their approach is shaped not only by the scientific method but by cultural ideas, some of them from science fiction. In turn, ­Helmreich argues, marine biologists’ scientific narratives enter the popular culture and shape our understanding of the ocean.

One of the pleasures of Alien Ocean is Helmreich’s playfulness. ­Steinbeck and ­Melville are touchstones, as are Star Trek and the Chemical Brothers. As Helmreich reminds us, the ocean in Western culture has always been seen as a “massive other,” frightening and full of monsters. For 19th-century Americans, the whale was the symbol of the sea: dangerous, but also an emblem of commerce, trade, and adventure. In the last century, the dolphin was the ocean’s lovable mascot, a symbol for the environmental movement. Now, in the age of gene sequencing, anxiety about climate change, and overfishing, as whales and fish become extinct while new bacterial species are discovered at a rapid pace, the ocean is “less full of giant monsters,” Helmreich says. “The oceanic sublime is becoming the oceanic slime.”

Ocean microbes promise an understanding of our origins, a source of new drugs and cosmetics, and a better understanding of how Earth’s climate is regulated (in part through the large-scale efforts of methane-­eating microbes studied by MIT professor Ed DeLong). But the ocean is still mysterious and scary. ­One scientist suggests that ­bubbles produced by methane-­generating bacteria in the Bermuda Triangle drastically decrease a ship’s buoyancy, perhaps causing the area’s notorious shipwrecks. In the ­middle of the night, which is when Helmreich sailed over the Bermuda Triangle, the ocean still seems as dangerous as it did to Melville. As a shipmate tells Helmreich, being on the open ocean is “the closest you can get to outer space without leaving Earth.”

But if the ocean now looks alien, so too do we. Just as the oceans are full of bacteria, we’re now told that our own bodies are, cell by cell, close to 90 percent microbial. “The ocean is a fun-house mirror that reflects another version of ourselves,” says ­Helmreich. The same forces that are reshaping our understanding of the ocean–be they science fiction or science fact–are also reshaping our understanding of what it means to be human.