Free Fire on the Horizon by Tom Shroder

the nascent North American continent as it drifted away from Europe and Africa. With the Atlantic Ocean slowly growing larger, the nearly enclosed sea that would become the Gulf of Mexico remained remarkably unchanged. The giant rivers that fed nutrients from the eroding land into its warm confines created an explosion of life, most of it microscopic. Contrary to popular myth (and oil company logos), dinosaurs only ruled certain terrestrial neighborhoods of earth—and their corpses didn’t turn into oil. In many ways the most significant impact onthe planet has always been from the smallest life-forms, not the largest. Microorganisms produced the oxygen that transformed the earth’s atmosphere. And microorganisms are largely responsible for the formation of oil and natural gas deposits, the burning of which is altering the atmosphere once again.
    At any given moment, microscopic ocean life accounts for a larger number of living organisms than there are stars in the universe. It’s been that way for three billion years. Every drop of water in the ocean contains more than a million microscopic organisms. While alive, most of these organisms employ ingenious strategies to keep themselves near the ocean’s surface, where they can transform sunlight into food via photosynthesis. They ride the currents, take advantage of the wind and wave-induced turbulence, propel themselves with tiny whiplike paddles, or even create their own buoyancy by pumping lipids between their cellular membranes. But when they die, the quest for sunlight ends and they drift into the darkness of the deep, to the bottom, where they collect and decay by the trillions of trillions.
    The balance between collection and decay is crucial. Certain conditions, the ingredients the Gulf has always offered in abundance, kick the bloom of microscopic ocean life into high gear: warm water, upwelling currents, and the inflow of nutrients. In combination, they spark an orgy of creation and a spike in the microbial population. All that life brings on an avalanche of death. The dead cells rain down in a blizzard—it’s actually called “marine snow”—and accumulate on the bottom faster than they can decay. Compressed and covered by the sediments pouring in from the rivers, the thick mat of sludge is cut off from oxygen, which over time might have burned the biomass away. Instead, the accumulated weight keeps pushing the organic matter deeper into the earth. The heat and pressure of the earth’s core begin to crush and cookthe molecules themselves, squeezing them into a series of ever simpler forms until, after many millennia, they reach their ultimate simplicity. Crude oil. Natural gas. Or methane, whose molecular composition is elegant simplicity itself, a single carbon atom surrounded by a pyramid of four hydrogen atoms.
    Now much lighter than everything surrounding them, the liquid hydrocarbon reservoirs exert a powerful upward pressure as they struggle to rise to the surface, a geological version of CO 2 bubbles in a glass of Coca-Cola. They migrate through tiny cracks and fissures or slide up along the inclines separating layers of rock until they reach the surface. Scientists estimate that every year 500,000 to 1.5 million barrels’ worth of oil and natural gas seep into the Gulf of Mexico—that’s about double the range estimated for the spillage from Exxon Valdez .
    In geological time, most oil eventually evaporates. Some geologists believe the Ohio River valley may have once had oil deposits as extensive as those in the Middle East. Now, of course, they are long gone.
    But as the hydrocarbons slide along the underside of impermeable barriers toward the surface, sometimes they get stuck. They slide up a slope made of nonporous rock or compacted salt deposited by shallow ancient seas, seeking higher ground, only to find the incline has become a trap. These traps are dome-shaped deformations, inverted cups where hydrocarbons slowly collect, eventually