Plate tectonics has its own version of the circle of life. Outlined by geologist J. Tuzo Wilson, the Wilson Cycle describes the birth and death of the ocean basins that separate continents. Continental plates rift apart along a volcanically active boundary that will eventually become the mid-ocean ridge. New oceanic crust is continuously formed at the ridge as the plates drift farther apart, forming a growing ocean basin. At some point, however, the growth stops and the oceanic crust begins to be subducted back beneath the continental plates. This continues until—like cartoon lovers sharing a spaghetti noodle—the continents meet.

Most of the stages of the Wilson Cycle can be seen somewhere in the world today. Africa is splitting along the East African Rift, which will someday separate the Horn of Africa from the rest of the continent. The Red Sea between Africa and the Arabian Peninsula is a little further along in the same process. The sea that once existed between India and Asia is gone now, a victim of the violent collision that's now driving up the Himalayas.

The Atlantic, however, might be at a poorly understood stage that we don't really have another example of. The Atlantic Ocean was born during the break of Pangaea 200 million years ago. Along all the Atlantic coasts of Europe, Africa, and the Americas, the continental and ocean plates are basically glued together—a plate boundary known as a passive margin. (Much about these coasts, from their gently sloping elevation to the lack of seismic and volcanic activity, is a result of this.)

Eventually, the passive margins will become active subduction zones. That’s the bit we don’t quite understand. There’s no obvious reason that subduction should just spontaneously begin at a passive margin. Some potential explanations call for outside forces—tectonic pushes or pulls from outside the ocean basin—to get things moving. Another possibility is that neighboring subduction zones spread into the ocean basins like growing vines. The authors of a recent paper in Geology think there may be just such a vine near the Strait of Gibraltar.

There are actually several small areas in the Atlantic where subduction is taking place, most clearly at the Lesser Antilles in the Caribbean and South Sandwich Islands arcs (between the southern tips of Africa and South America). It appears that the Gibraltar area may be nibbling at the Atlantic as well.

There is subduction going on in the Mediterranean, where Africa is headed for a collision with Europe, closing the sea between them (which once was much larger). The rocks that form the shorelines along the Strait of Gibraltar are actually on the oceanic plate trapped between the two continents. While it’s being squeezed from the north and the south, this portion of the plate is also moving west toward the Atlantic, subducting oceanic crust as it goes.

By examining seismic imagery (which generates pictures of subsurface layers based on how they reflect sound waves) and high-resolution seafloor bathymetry, the researchers have mapped out the way the oceanic crust is deforming and faulting in the area. They say there are several ways this boundary could evolve in the future, but they think it will continue migrating west and then spawn more significant subduction, which will spread to the north and south.

If it does develop that way, it (and other features like it) might eventually help the Atlantic Ocean transition from middle age into the closing stage of the Wilson Cycle. More work will enable us to better understand how likely this scenario is, but the ultimate test—waiting around to see what happens—will take a bit longer than any of us have on this Earth.

Geology, 2013. DOI: 10.1130/G34100.1 (About DOIs).