The Galápagos Rift was a promising site because it is part of a highly volcanic undersea rift cradled by a complex, globe-encircling chain of mountain ranges called the mid-ocean ridge system. Over 40,000 miles [65,000 km] long, this colossal system weaves around the entire planet like the seam on a tennis ball. Were the oceans stripped away, it would “easily [be] the most dominant feature on the face of the planet, extending over an area greater than that covered by all major terrestrial mountain ranges combined,” writes Jon Erickson in his book Marine Geology.

A particularly significant feature of the mid-ocean ridge system is that it is essentially a twin system—two mountain ranges running parallel to each other and rising 10,000 feet [3,000 m] above the ocean floor. Between the ranges are the greatest chasms on earth—canyons up to 15 miles [20 km] wide and 4 miles [6 km] deep—four times deeper than the Grand Canyon of North America! At the foot of these chasms lie highly volcanic rift zones. When scientists first studied the Atlantic segment of the ridge system, called the Mid-Atlantic Ridge, their instruments revealed such intense volcanic activity “that it seemed as though the Earth’s insides were coming out,” says Erickson.

The plates move in relation to one another. Where they draw apart, they thin out and form the rifts of the mid-ocean ridges. Worldwide, plates move at an average of about one inch [3 cm] per year.

According to the plate tectonic theory, as the plates diverge along the ridge system, they allow hot rock from the mantle, the region below the crust, to rise. The hot material forms new oceanic crust along the rift zone, but this does not result in the plates’ fusing together. Instead, they continue to part, which makes the rift system resemble a massive wound that never heals.