Maurice Ewing was a Texas-panhandle farm boy, became a geophysicist, and then and oceanographer. He conducted the first marine seismic acquisition, inventing the equipment he needed as he sailed the oceans. I find it odd that a lad from the grasslands spent years at sea, but apparently Ewing himself never found it strange. Early in his career, in 1936, he found himself aboard the Barracuda, an oceanography research submarine plying the Caribbean. Also aboard were two other phenomenal young geophysicists, men who would revolutionize the way we understand the planet. These were Edward Bullard, of Cambridge, and Harry Hess, from Princeton. Had the Barracuda floundered, geologists might still be opposing continental drift. But it didn’t and these men led discoveries that rewrote earth history.
Submerged, but floating above the second deepest hole in the world, the trio were helping a senior scientist, Felix Venig Meinesz. The team was trying to make sense of the Puerto Rico Trench, an almost bottomless gash in the seafloor, and now recognized as an island-arc trench. At 8648 metres (28,373 feet), the subducting trench is the deepest sink not in the Pacific. It was the sink in the Devil’s kitchen. Meinesz, a Dutch geodesy expert, was there to study gravity because that’s what geodesists mostly do.
Meinesz was nearly seven-foot, subs those days were built for men at least a foot shorter. So Meinesz bent himself over for days at a time, sometimes crawling on his knees in the borrowed US Navy submarine. For a while, working aboard a submarine was the only way Meinesz could get good gravity readings at sea. On surface, waves pitched and rolled ships. They didn’t provide the stability needed to get good gravity data. (Try to weigh yourself on a bathroom scale while swaying around. It doesn’t work.) Below the roiling surface, the sub was almost tranquil.
To get a gravity reading, Meinesz carefully calibrated a pendulum, swung it to one side, then timed the period of each round trip of the weight hanging on the end. A skilled operator with a well-engineered pendulum gravimeter could find the tiniest changes in gravitational force as the device was moved from place to place. Those changes were due to varying density in the material below the seafloor. Eventually Meinesz – the consummate physicist and tinkerer – built a gravimeter that ignored the rocking waves. Likely his height motivated him to eventually finish a new design that would allow him to unfold and work at sea level.
Aboard the USS Barracuda, Ewing, Bullard, Hess, and Meinesz gathered geophysical data over that incredibly deep trench. They found a gravity anomaly – an unexpectedly low reading. This told them that something very peculiar was happening on the seafloor. It was thirty years before subduction zones were discovered, but Hess and Meinesz had a prescient hunch. The low gravity reading could signal lighter rocks were intruding into the ocean’s crust. Although they didn’t diagnose the subduction zone, the two concluded that the seafloor was somehow active. They figured something was moving down there. This intuitive realization went against centuries of accepted wisdom that the oceans were dull, permanent, immobile washbasins. From inside the Barracuda, under the tropic Caribbean waves, the world was changing. In more ways than they could imagine.
This story continues in The Mountain Mystery.