Passage II

SOCIAL SCIENCE: This passage is adapted from Great Waters: An Atlantic Passage by Deborah Cramer (©2001 by Deborah Cramer). The Sargasso Sea is a part of the northern Atlantic Ocean.

As the Cramer idles through the Sargasso Sea, waiting for the wind to rise, the sea is flat and empty. Nothing demarcates or divides the smooth expanse of water dissolving into the horizon. This vast, unroughened surface, this breadth of uniform sea, deceives. But for a few lonely oceanic islands, the unperturbed surface offers no hint of the grand and sweeping energies hidden below.

Only one thousand miles offshore, the Cramer has already sailed through some of Atlantic’s deepest waters. Contrary to what one might guess, Atlantic’s deepest waters, like those in other oceans, are along her edges. As we continue east, toward the middle of the sea, the bottom rises. The unmarked plains of the abyss, here flattened by layers of sediment, give way to rising foothills and then to mountains. The first maps of Atlantic seafloor noted, albeit crudely, this rise. Early efforts to plumb Atlantic’s depths proved outrageously inaccurate: one naval officer paid out eight miles (thirteen kilometers) of hemp rope from a drifting ship and concluded the sea had no bottom. Eventually, sailors more or less successfully calculated depth by heaving overboard cannonballs tied to bailing twine. When they hit bottom, the sailors measured and snipped the twine and then moved on, leaving a trail of lead strung out across the seafloor. These crude soundings, forming the basis of the first map of Atlantic’s basin, published in 1854, identified a prominent rise halfway between Europe and America.

For many years no one could explain why the basin of Atlantic, unlike a bowl, deepened at its edges and shoaled in its center. People assumed that this “Middle Ground,” “Telegraph Plateau,” or “Dolphin Rise,” as it was variously called, was an ancient and drowned land bridge, or a lost continent, but sailors repairing transatlantic telegraph cable unknowingly produced evidence to prove otherwise. Wrestling with the broken cable, they accidentally twisted off a piece of the “plateau” and dredged up a twenty-one-pound (ten-kilogram) chunk of dense black volcanic rock. It was some of the youngest, freshest rock on earth, and it was torn not from a piece of continent sunk beneath the waves, but from the very foundation of the sea.

Today, highly sophisticated sound waves bring the hazy images of those early soundings into sharp focus, revealing that one of the largest and most salient geographic features on the planet lies on the floor of the ocean. Hidden beneath the waves is an immense submerged mountain range, the backbone of the sea. More extensive, rugged, and imposing than the Andes, Rockies, or Himalayas, it covers almost as much of earth’s surface as the dry land of continents. Winding like the seam of a baseball, it circles the planet in a long, sinuous path, running the entire length of Atlantic, slashing the basin neatly in two. Its mountains are stark and black, as black as the sea itself, lit only at their peaks by a thin, patchy covering of white, the skeletal remains of tiny microscopic animals that once lived at the surface. Peaks as high as Mount St. Helens sit in a watery world of blackness, more than a mile below the surface, beyond the reach of light, beyond the sight of sailors.

A great valley, eclipsing any comparable feature on dry land, runs through these mountains. Arizona’s Grand Canyon, one of earth’s most spectacular places, extends for about 280 miles (450 kilometers). A lesser-known canyon of similar depth but considerably greater length lies hidden in the mountains of the ridge. Although offset in many places by breaks in the mountains, the rift valley, as the canyon is called, extends the length of Atlantic for 11,000 miles (17,700 kilometers). Here in this bleak and forbidding place, where the water is almost, freezing, subterranean fires have lifted mounds of fresh lava onto the seafloor. Scientists visiting the rift valley for the first time named the volcanic hills in this otherworldly setting after distant, lifeless planets.

Yet, what had seemed so foreign to scientists is an integral part of earth’s very being, for at the ridge our own planet gives birth. The floor of the rift valley is torn; from the gashes has sprung the seafloor underlying all of Atlantic. Here the youngest, newest pieces are made. Earth is still cooling from her tumultuous birth four and a half billion years ago. Heat, leaking from the molten core and from radioactive decay deep inside the planet, rises toward earth’s surface, powering the volcanoes that deliver the ridge to the sea.