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But Dick, a young graduate student on that first effort, refused to give up. He devised a new strategy to drill on Atlantis Bank, a curious sunken island in the undersea mountains in the Indian Ocean. There, he believed, lower crust and mantle rocks lay closer to the surface, leaving less rock to drill through to reach the Moho.
More than three decades later, Harry Hess, a Princeton geologist who enlisted as a naval officer during World War II, entered the story. As his ship crisscrossed the Pacific transporting troops, he turned on an echo-sounder that continually imaged the seafloor. It revealed undersea mountains, mid-ocean ridges, and deep trenches.
But what exactly happens at the Moho? Over the years, scientists analyzed seismic waves used to probe into the seafloor, or they examined segments of seafloor, called ophiolites, that had been thrust up onto land by tectonic forces. They saw evidence that ocean crust has a structure resembling a three-layer cake. Right above the Moho, magma cools and crystallizes into a layer of rocks called gabbro. Above that is a layer of hardened vertical sheets of surging molten rocks called dikes. The icing on top is composed of rapidly cooled lava that erupts onto the seafloor as pillow basalts.
In 1961, near the island of Guadalupe off the west coast of Mexico, a rig on a barge drilled in 11,673 feet of ocean, through 558 feet of sediments lying atop the seafloor, and into 43 feet of basalt rock at the top of the ocean crust.
But this initial victory was quickly followed by frustrating and expensive technological challenges. Keeping a ship in the ocean in one position was hard. Fractured rocks fell into holes, often sealing them and forcing the scientists to start anew. Drill bits broke and pipes bent, and valuable equipment was lost in the deep. As cost estimates to continue the project mounted to $64 million and then $122 million, Congress abruptly killed funds for Project Mohole in 1966, and the scientific crusade to reach the Moho seemed irretrievably dead.
At the conference, Robert Coleman, a prominent geologist, told Dick and an impressionable group of graduate students about the nascent Ocean Drilling Program (ODP). Though it had failed, Project Mohole had established ocean drilling as a viable and valuable scientific pursuit. The project successfully developed a lot of technology, including a way to drill through water; a system of thrusters and acoustic signals that could keep a ship stationed above a hole; and re-entry cones that allowed scientists to keep replacing worn drill bits and reinserting them into the same hole.
In 1986, they surveyed a potential target in the Indian Ocean: Atlantis Bank, a place where a huge segment of deep ocean crust had slid upward on the ramp of a tectonic fault, beyond the lavas and dikes of the upper crust. It moved up so high, in fact, that at one point in geologic time, it broke above the sea surface and formed an island before subsiding under the sea again. At Atlantis Bank, the fractured rubbly debris created by faulting had been eroded away, exposing a surface of coarse lower-crust gabbro, which proved easy to drill.
At the end of the string are a four mace-like circular drill bits with a circular space in the middle. The bits rotate to pound down and around a thin cylinder of rock, forming rock cores 10 feet long by a few inches wide. As the drill goes down, the core samples are pushed up into the space between the bits. A device called a core catcher pulls the rock samples back up the pipe string to the ship, so scientists can analyze them.
Dick and company were having a difficult time figuring things out on their 1987 expedition. They drilled several unsuccessful holes and were taking heat from scientists on shore who were keeping track of the proceedings. With time for the expedition running out, Dick scrutinized sonar maps of the seafloor and spotted a hopeful target.
Ocean crust in the Pacific does appear to have the neat three-layer-cake structure: gabbro, dikes, and basalt. But Indian Ocean crust looks like a cake that a throng of partygoers grabbed and shredded into a mishmash.
In the Pacific, Dick explained, a steady stream of buoyant hot magma continually rises, transitioning through a series of chemical and physical changes to make crust resembling layer cake. Then the newly formed ocean crust spreads out laterally on either side of mid-ocean ridges.
In the Indian Ocean, however, magma rises and crust forms in a far more dynamic arena. As the plates move apart, large blocks of crust are sliding up, down, and against one another on massive faults, smashing, cutting, and intruding into one another to create even more fractures. Magma is squeezed through these fractures, filling in the spaces, zigzagging and crystallizing and adding more disorder to the jumbled crustal tapestry.
The findings also presented the first clues of another fundamental discovery that Dick and colleagues pursued: The reason ocean crust was different at different mid-ocean ridges is that the ridges spread apart at different rates. Ridges in the Pacific are fast-spreading; Indian Ocean ridges spread very slowly.
Mantle rock that has been uplifted and exposed to seawater and reduced pressure is chemically altered. The holy grail for scientists is to get their hands on a sample of unadulterated mantle rock right from the source.
A decade would pass before Dick could revive the quest to the Mohole with an expedition in 1997 to Atlantis Bank aboard the JOIDES Resolution. The cruise began auspiciously. Drilling proceeded nearly a mile into the seafloor. Then disaster struck.
Finally, he got approval for the SloMo Project to drill to Moho at the slow-spreading Southwest Indian Ridge in two phases. In December 2015, Dick, at age 69, returned to Atlantis Bank aboard the Resolution, serving as co-chief scientist with Chris MacLeod from Cardiff University in the first leg of a new attempt to drill a hole to the Moho. Once again, difficulties arose. Three of the four heads of the drill bit broke off right at the start. Then the ship had to cease operations for several days and steam toward shore to evacuate a technician who needed medical attention.
The expedition drilled to a depth of 809.4 meters, about 2,665 feet or a half-mile, beneath the seafloor. It was about half as far as they had hoped, but they came away with hopeful signs. They recovered a solid 10-foot piece of gabbro from beneath the ocean floor.
The reactions also cause valuable minerals such as copper, silver, gold, and zinc to leach out of rocks. They concentrate the minerals into hot, buoyant hydrothermal fluids that rise in hot springs on the seafoor, where they cool, solidify, and are deposited in massive mounds of metal sulfide minerals. Sections of such mineral-rich seafloor crust have been uplifted onto land by tectonic forces and have been mined for thousands of years; now industry is starting to explore mining them on the seafloor.
Carefully, with gloved hands, she removed the object from its stone niche, where it had rested for centuries deep underground, inside the dormant volcano where the mysterious Icelandic cult that guarded it made its home. It hardly weighed anything. Surely the tingling she felt from it was her mind playing tricks. Merely the anticipation of finally having it in her possession. Nerves, that was all.
The Aetherian engine in the back of the airship whined, throwing off green-tinted sparks behind it. When the gondola came alongside the mouth of the tunnel, the door to the cabin was wide open, and there was Marlowe, just like he was supposed to be. The pilot was obscured, made larger and more terrifying by the greatcoat and leather-padded goggles masking his features. He held his rifle at the ready.
Marlowe turned another set of levers and the sound changed, drive motors coming online, whirring, moving the craft laterally. The mountain, its black crags and broken clefts, slid past, like a painting on a roller. In moments, the ship turned to the coast of Iceland, and open sky lay before them.
The bench seat was hinged, revealing the promised cupboard, packed tightly with boxes, slots, canvas bags, blankets and fur coats for high altitudes, provisions for an extended journey, and her own package of supplies. Good. In a slot that looked as if it had been specially made to enclose it, she found the bottle of brandy and a pair of glass tumblers.
She joined him at the front of the cabin. The dashboard had enough of a ledge for her to set the tumblers on it and pour. After, she tucked the bottle in a pouch on the wall to keep it from sliding or falling. Marlowe took the glass before she could hand it to him.
Once the sky darkened, the first signs of battle became visible. On the eastern horizon, tracers arced, distant shooting stars, orange, yellow, green. Fireballs rose up from unseen explosions and dissipated into raining sparks. At the moment, the scene was a remote tableau, an unreal moving picture. She could imagine the hint of pyrotechnics was a harmless show put on for her benefit. Except for all the thousands of people dying underneath it.
Dim lamplight turned the cabin ghostly, flat, unreal. She wrapped the blanket more tightly around her. For the moment, she could believe she drifted between worlds, and oddly enough the sensation came as a relief. In this suspended place, she could breathe easy, let down her guard, and pretend that all was well.
An explosive scream cut through the air, and in spite of herself Harry flinched back. When she looked, she saw the long trail of black smoke, but never saw what made it. The trail led to the enemy airship, which transformed into a fireball a moment later. The heat of it washed over her, and she ducked, clinging to her line, pulling herself close to the cabin for shelter. The Kestrel rocked with the shockwave, but Marlowe increased altitude yet again and got them above the worst of it. Breathing was very difficult now; blackness flashed at the edges of her vision. It was all wind and no air up here.
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