Gibraltar might be the beginning of the end for the Atlantic Ocean

View to the south across the Strait of Gibraltar.

José Rambaud

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.)