By Dr. Robert Thorson

The tragedy in the Gulf of Mexico is a classic case of human error. We are all to blame. We will all live with the consequences, albeit unevenly.

The media sees this mostly as a human story: the ducking-and-covering by politicians with respect to offshore drilling; the blame-shifting from stockholders to executives to subcontractors; the blurring by attorneys between what’s right and what’s legal; the rationalization by members of Congress that this is a freak occurrence unlikely to happen again; the failure of the U.S. Minerals Management to manage; the shortsightedness of tea party libertarians who see less regulation as better regulation; the enduring hubris of overconfident engineering; and a cultural addiction to petroleum.

At times like this, I feel like shutting off the power to my house and buying a goldfish for commiserative company.

Beneath the media drama is the geology, which can help us understand. Spills are not leaks. They are always caused by human error. For example, when the Exxon Valdez struck a well-charted reef in Prince William Sound, Alaska, spilling 11 million gallons of oil. In contrast, leaks are usually slow and often natural: drip, drip and drip. The upward leakage of natural gas and petroleum from deep reservoirs to the biological domain of land and sea is part of geology in general, and the carbon cycle in particular.

My favorite oil leak took place at Rancho La Brea, in Los Angeles, Calif. There, oil seeped upward between 40,000 and 10,000 years ago to pool on the sun-baked surface. After thickening into tar, this petroleum product entombed a succession of local ecosystems, complete with the skulls of saber-tooth tigers and the giant sloths they preyed upon. A molasses-colored liquid cooked from the marine fossils of one era leaked upward to make terrestrial fossils of a younger one. In the distant future, a Gulf Coast pelican killed by the deep water leak today will likely reappear as a tar-covered fossil.

My second favorite leak occurred at Titusville, Pa., in the mid-1850s. There, petroleum pure enough to light lamps was seeping out of ground. Then, in 1858, Edwin Drake drilled through an island in Oil Creek to create America’s first petroleum well. He worked for what had originally and aptly been named the Pennsylvania Rock Oil Company. The goal was to make lamp oil from this geological reservoir, rather than from the thousands of blubbery reservoirs swimming around as whales and porpoises. Though I’m saddened that these cetaceans are being killed indirectly by oil today, I’m heartened by the fact that we no longer kill them directly for oil, as we routinely did less than two centuries ago.

Liquid oil can’t be mined. Instead it must be drilled for. So downward we bore until we reach a reservoir of rock porous enough to hold and transmit fluids. Such reservoirs are filled from the top down with gas, oil and brines that rose upward from greater depths where organic-rich source rocks were being slow-cooked to the threshold of releasing fluids. To prevent the upward escape of fluids to the surface, each reservoir must be capped by an impermeable membrane, normally composed of a layer of clay-rich mud.

Every petroleum well is an artificial leak drilled through cap-rock, and powered by buoyancy and pressure within the reservoir. When engineers maintain control, they have a productive oil well. When they lose control, they have a disaster, especially if the pressure is high and the well is under water. Leaks continue until they’re plugged, or the reservoirs are emptied.

Petroleum killed terrestrial creatures at Rancho La Brea, and aquatic creatures in Oil Creek. What’s different about the present disaster is the magnitude of the potential damage to multiple ecosystems and human economies. Today, I’m ashamed of my species.

But history gives me hope. After the Stone Age came the Bronze, Iron, Coal and Petroleum Ages. The petroleum peak has passed. Fortunately, we’re heading into a different era