In 1987, in a laboratory of the Scottish Marine Biological Association in Oban, Scotland, geologist John Parkes opened a series of 20-ounce cans that had been shipped to him from Peru. Inside each was a two-inch-thick disk of mud. Parkes was dressed warmly, because he was working in a chilly room at 60°F. Geochemists on the drill ship, on the expedition led by Suess, had cut slices from several drill cores with sterile knives, capped them, flushed them with nitrogen to banish all oxygen, sealed them in cans, and sent them to Oban.
Parkes opened the cans and extracted tiny cores from each. In those tiny cores he found that he could detect bacterial activity—the reduction of sulfate to smelly sulfide, for instance. Staining minute samples of sediment with a fluorescent dye that binds to DNA, he found he could count cells under his microscope, just as Boetius would do with her Hydrate Ridge samples many years later. At the time no one had done this with drill cores. And when all of it was done, says Parkes, “we’d discovered 10 percent extra biomass on Earth.” More recent estimates place it at more like 30 percent.
Parkes’s peers did not rush to anoint him. For decades geochemists had been reporting that sulfate and methane were mysteriously vanishing in sediments. For decades, too, petroleum geologists had been reporting that some kind of microbe seemed to be chewing up oil in deep reservoirs. “These facts were staring us in the face, but nobody put it all together,” says Parkes. When he did, it was suddenly controversial. People suspected that his samples were contaminated by surface bacteria. They refused to see the whale.
They see it now. Two years ago the drill ship Joides Resolution went back to the same waters off Peru where Parkes’s first samples had been taken. This time Parkes was on board, along with a dozen other microbiologists and a few geochemists, including Dickens. It was the first expedition specifically designed to study the deep biosphere. And the first result was simply to confirm what Parkes had been saying all along. “There are masses of bacteria down there,” says Bo Barker Jørgensen of the Max Planck Institute, who was cochief scientist of the expedition.
The researchers found microbes in all the sediments they examined. There were more under the coastal waters of Peru than in the open Pacific; more near the seafloor than 1,400 feet below it. But there were intact microbes everywhere. In the upper layers, typically, they were reducing sulfate; in the lower ones they were making methane; and in between they were oxidizing methane.
The existence of the deep biosphere is established—but it remains an astonishing paradox. “From all we understand about the energy requirements just to stay alive, it’s much higher than the energy they have,” says Barker Jørgensen. If the deep microbes spend as much on maintenance as surface microbes do, he says-repairing radiation damage to their DNA, keeping their membranes intact—they should have nothing left for the microbial prime directive: divide and multiply. Barker Jørgensen’s expedition looked for some new energy source in the sediment, some exotic new combination of fuel and oxidant, and found none.
Parkes thinks the microbes’ secret is their slowness: “These things are dividing every thousand, ten thousand, hundred thousand years. There’s nothing to eat them; bacteria near the surface have to grow fast because they get eaten by protozoa and ciliates, but we’ve not detected those kinds of organisms in the subsurface. So bacteria there can concentrate on maintenance, rather than wasting energy on division.” And yet they must have lived long enough and divided often enough and mutated often enough to evolve through natural selection, because they are well-adapted to their environment. Parkes has found microbes in deep sediments that grow best at precisely the pressure at which he found them. “They are responding on geological timescales,” he says. “That’s the fascinating thing.”
Microbes living under the seafloor today, Parkes speculates, may have survived the growth and splintering of continents, the opening and closing of oceans; they may have been buried, subducted, frozen in hydrate, and spat out of a mud volcano, only to be buried, subducted, and spat out again. While we were waiting for our evolutionary fast lane to be paved, racing through all of human prehistory and history in the time it takes one of them to divide once, they have been living in time with the planet’s deepest, slowest rhythms. They have been living almost like rock, which is precisely what made them so easy to miss. They have always been there, from the deepest past, but only now have they finally penetrated into our awareness. Given their collective influence, it’s about time.
