The Big Thirst, page 5
Here’s the thing that’s a little hard to grasp: Once you squirt that oxygen-hydrogen pair and that lone hydrogen into the crystal lattice of a rock, buried three hundred miles down, in what way are those atoms still water?
Steven Jacobsen, a geophysicist at Northwestern University, is a gracious host to this world of heat, pressure, and darkness that is almost completely inaccessible to humans. Jacobsen has used an enormous press (the kind you can make artificial diamonds with) to mimic the pressures and temperatures three hundred miles down and to squeeze water right into rock. He is devoting a large chunk of his career to studying the importance of wet rocks deep inside the Earth.
Q: So this idea that there is water inside these rocks—inside the structure of the minerals—is this a theory or a fact?
JACOBSEN: Oh, this isn’t a theory. It’s reality. Absolutely.
Q: And if the water is inside the molecular structure of the rocks, why do you scientists think of it as water? In what sense is it still water?
JACOBSEN: Well, it’s not water by any stretch of the imagination, of course. We use that term very colloquially.
Q: But it really is water, in fact?
JACOBSEN: Yes, it’s water, unquestionably. If you release the pressure and temperature, the hydrogen and the OH come out as water. If it’s not in the rock, it’s water. It is where most of the planet’s water might be, in fact. In the rocks.
The graphic-novel version goes something like this: In the right conditions of temperature and pressure, certain kinds of rocks literally suck water into their structure, much the way a sponge sucks up water. As the water goes into the rock, it dissociates—the H goes here, the OH goes there.
There is absolutely water in these rocks, and the scientists know it in at least three ways: These hydrated minerals are literally more pliant, more puttylike, than in their unhydrated state; the scientists can measure water’s pieces inside the structure of the rocks using infrared spectroscopy; and most important of all, when the pressure and temperature on the rocks are released in the right way, the H and the OH come squirting right back out of the rock, and they come out as water.
And here’s the thing: Scientists think they have figured out that these kinds of watery rocks are common in a band inside the Earth stretching from about 250 miles deep to about 400 miles deep, a layer 150 miles thick, a lot thicker than the film of water on Earth’s surface.
“Even if only 1 percent of that rock is water,” says Jacobsen, “that’s a lot of water, several times Earth’s oceans, in fact.”
Hundreds of scientists around the world are studying the physics of Earth’s deep water, and its impact. While water in this fourth state, this deep water, may be out of sight, while it may be harder to study and harder to understand than the water NASA discovered in 2009 on the Moon, Earth’s deep water is directly connected to the water crashing ashore at the Santa Monica Pier or the White Cliffs of Dover, the storm clouds crowding the horizon in Johannesburg or Shanghai.
EVERY SCHOOLKID IS FAMILIAR with the cheerful drawing illustrating the basics of the water cycle: Clouds drop rain or snow on the flanks of mountains; water runs off into streams and rivers and lakes, and then into the ocean, from which the beaming sun evaporates it (often in the form of lines that look like wiggling snakes rising straight into the air) to become clouds again. Precipitation, evaporation, precipitation.
The diagrams are always a little cartoony. The actual process itself is awesome, even majestic. The volumes of water that the Earth and the Sun are moving around are Olympian, so large they are measured in a unit rarely heard in the ordinary world: cubic kilometers. A single cubic kilometer, an imaginary cube one kilometer on a side, holds an incredible amount of water: 260 billion gallons, enough to cover the island of Manhattan to a depth of thirty-seven feet.
Every hour, on average, Earth’s oceans are evaporating 50 cubic kilometers of water into the air (13 trillion gallons). The entire United States uses only 410 billion gallons of water a day for all purposes—so every two minutes, the oceans create more clouds of fresh water than Americans use in twenty-four hours.7
Just the leaves from a single acre of trees might send eight thousand gallons of water up into the air in a day, enough to fill two-thirds of a typical backyard swimming pool.8
A molecule of water that evaporates into the air—from a fountain, from a puddle, from your skin—spends about nine days floating in the sky before returning to Earth as rain or snow.9 Half the Earth’s surface is typically covered by clouds, with the life of a particular cloud usually being no more than an hour.10
And how much water is floating up there in those fat black rain clouds, literally defying gravity until the rain falls? It is lakes full of water. If just an inch of rain falls on your half-acre yard, that’s 13,577 gallons of water— one inch, one storm, one small patch of ground.11
Perhaps the most mind-bending fact that shows up on the standard water distribution charts is something identified cryptically as “biological water.” It’s a small number, just 1,120 cubic kilometers—one-tenth the water cycling through the atmosphere at any moment, enough water to fill just one of the five Great Lakes (Erie).12
What is “biological water”?
It’s the amount of water ziplocked into the bodies of everything alive on the planet—earthworms, squids, pelicans, mosquitoes, pythons, giraffes, sardines, hippos, the swine flu virus, not to mention all the Earth’s trees, ferns, flowers, and grasses. And inside us too. That 1,120 cubic kilometers comes to 300 trillion gallons of water. Given that the average human—considering adults and children—contains about 5.5 gallons of water, people account for only about 38 billion of the 300 trillion gallons of “biological water.”13
Putting aside the question of how a scientist could calculate the total amount of water inside all the creatures in Earth’s biosphere, it’s a humbling number. Of all the water doing life-support duty, 99.9987 percent of it is inside creatures besides us.
One funny thing about the numbers describing how much water is streaming through the world—the total water volume for the Earth’s surface, the total frozen in glaciers, the total evaporating annually from land, the total inside crocodiles and poodles—is how precisely the numbers agree, no matter which source you consult. On the Web site of the U.S. Geological Survey, in grade school curriculum materials, in science textbooks, across the Internet, and even in a handmade table taped to the wall of a professor of natural resource sciences at the University of Adelaide in Australia—everywhere the numbers are exactly the same. It’s not just hard to believe the precision and lack of variance, it’s impossible. You can’t get complete agreement on a number as fixed as the diameter of the Earth, a measurement that doesn’t change as much as, say, the annual evaporation of water from the Indian Ocean. Almost none of the charts with the amazing numbers list sources—or they reference each other— but one indicates that the numbers are the work of a man named Igor Shiklomanov, from a chapter he wrote for a book edited by the American water expert Peter Gleick in 1993 called Water in Crisis.
And if you go to Gleick’s Water in Crisis, there on page 13 is exactly the same chart everyone else prints. Except this one is the original. Igor Shiklomanov, a highly regarded Soviet water scientist, prepared the chart based on his own analysis, and the work of Soviet colleagues, with some of the data originally published in 1974. Right in the text of his essay in Water in Crisis, above the chart, Shiklomanov writes with all modesty, “It should be noted that the data on the amount of water on earth (as the authors of the cited monograph themselves note) should not be considered very accurate; they are only approximations of the actual values.”
Given that very clear caution, it’s not just amazing how widespread the water data have become. What is so startling is that given the incredible leaps in computer modeling, water measurement technology from space, and computing power—not to mention the intensity and importance of climate change science and its dependence on moisture in the atmosphere—no one has come up with a fresh set of calculations. Shiklomanov’s seventeen-year-old chart, based on data almost four decades old, remains the standard.14
The real gap in the water cycle drawings, of course, is not the uniformity or precision of the numbers, but as Steven Jacobsen and his deep-water colleagues would point out, that most of the water is missing. It’s in the mantle, and it, too, cycles.
Joseph Smyth is a geologist at the University of Colorado, one of the pioneers in trying to understand the dynamics and significance of deep water (he was also Steven Jacobsen’s thesis adviser).
The water in the deep interior rocks of the Earth’s mantle gets there through the oceans. “The most significant way this happens is in the ocean crust,” says Smyth. Along the ocean floor is a mineral called olivine. As it happens, olivine reacts with seawater to create serpentine—the green stone that might show up as your kitchen counters. Then, at the places where the continents are grinding into each other, the ocean floor is “subducted,” it’s shoved downward into the Earth’s interior by continental drift. The water-saturated serpentine dives into the crust, taking its load of water with it.
You could release the water from your kitchen counters by heating them (it would ruin the counters, however). That, in fact, is exactly how the deep water comes back to the surface, says Smyth. “It returns mostly through volcanoes. When there’s an eruption in the Andes or at Mount St. Helens—that big eruption cloud is largely water, with ash mixed in.” A volcano’s eruption cloud is often 70 percent or more water. “What’s making the explosion, in fact, is water coming out of the magma,” says Smyth.
Exactly how much water has come to be stored in the mantle is a mystery—and one of the questions scientists are trying to answer.
“What’s going on there is extremely inaccessible,” says Steven Jacobsen. To say the least. The deepest hole humans have ever drilled is 12 kilometers (7.5 miles)—and that took the Soviets twenty-four years of effort and $100 million.15 As of 2008, the world’s deepest mine, that is, the deepest people can actually travel inside Earth, is just 3.9 kilometers (2.5 miles).16 Both of those are barely finger scratches on the surface of the Earth. The interesting action in deep water is at about 410 kilometers. So all the research is done using sound waves and seismology, and also huge, powerful presses that can mimic the pressures and temperatures 410 kilometers inside the Earth, allowing scientists to create samples of the kinds of rock found there, which they can then study. Re-creating those conditions requires so much effort that a hydraulic press two stories tall creates rock samples the size of the period at the end of this sentence.
Even if there are four or five earth-oceans of water deep in the Earth’s mantle, it’s not like finding a huge reservoir of oil or natural gas. Deep water isn’t something humans can sample even to study directly, let alone tap it to irrigate a dry patch of the Sahara.
But the water has at least three critically important roles.
First, Smyth, from Colorado, thinks that this fourth state of water, locked inside rock, may be how the Earth actually got its original supply of water.
“I think most of the water came here as hydroxyl (OH) in the primitive meteorites called chondrites,” says Smyth. “There isn’t universal agreement on this. And some of the water came as molecular water”—as cosmic juice, that is—“but I think most of the water came from these chondrite meteorites, with the water in them as hydroxyl.” (It would still have to have been formed in space first, of course.)
The water that has come to blanket the Earth would then have been released by the planet’s early volcanism.
It’s an intriguing theory, and one possibility among several. But the question of how Earth’s water got delivered is a messy scholarly splash fight at the moment, with several passionate camps. Distinguished research scientists will actually shout, referring to colleagues who disagree with them, “Well, has he read my latest paper on isotope distribution? Has he? You tell him to read that paper and he’ll understand how it happened!”
Second, there is little question that the “wet rocks” deep in Earth’s mantle are vital for plate tectonics—the water reduces the viscosity of the rocks, and their resulting “plastic” quality enables the continents to slide beneath and over each other. Those sliding plates create the geology of much of Earth.
Finally, and perhaps most important, the deep water may be the only reason Earth is a blue planet at all.
“We’ve had relatively constant ocean volumes over time, going back at least 500 million years,” says Jacobsen. “Sea level does rise and fall, yes, but on the scale of dozens of meters.” Geologists call the part of the continents that crowns above the oceans “continental freeboard.” If you don’t fret too much about the edges of the continents (which, unfortunately, are where most of the people live), the amount of continental freeboard is remarkably stable going back hundreds of millions of years.
Considering that there might easily be five earth-oceans of water stored in the planet’s interior, that sea-level stability is intriguing. Even the release of a single earth-ocean—doubling the surface water on the planet—would swamp everything.
“Maybe the water in the mantle is why we have those oceans,” says Jacobsen. “We can’t extract and drink that water, but maybe the water in the mantle is buffering the amount of water in the oceans.”
The mechanism isn’t understood. But the importance is.
Jacobsen’s mentor, Smyth, goes back to Earth’s beginnings. “Early in Earth history, when it had these big violent impacts from meteors and comets, the atmosphere got blown off a few times during the first 100 million or so,” Smyth says. “It may be that Earth has retained water through the last 4.3 billion years by having this reservoir of water in the interior.
“If the water were just on the surface, there might not be any water on Earth now.”
PERCY SPENCER, an executive with Raytheon Manufacturing, was a self-educated orphan whose formal schooling ended at age twelve. An intuitive and brilliant engineer—Spencer ended up with 130 patents—he worked alongside MIT’s physicists developing technology for World War II, and his practical sensibility helped figure out how to mass-produce magnetrons, the electronic guts of the radar units whose widespread use helped win the war.17 As the war was wrapping up in 1945, Spencer was touring Raytheon’s lab in Waltham, Massachusetts, where magnetrons were being tested. He noticed that the Mr. Peanut candy bar he routinely carried in his shirt pocket to feed the squirrels was melting.
It was the kind of moment for which Spencer was famous—he knew that high-frequency radiation from the magnetrons had melted the candy bar. But rather than pass it off as a messy inconvenience, he was intrigued at the possibilities.
As the story is told, Spencer immediately dispatched a Raytheon office boy to buy a package of unpopped corn kernels. He put the unpopped corn in range of the magnetron, and in a satisfying moment familiar to every hungry office worker, the popcorn popped all over the lab.
Percy Spencer had discovered both the microwave oven and its single most distinctive cuisine in a single moment.18 Today, the working heart of a $39 microwave from Wal-Mart—the magnetron, which generates the microwaves—is the same as the technology that helped the Allies use the then-new radar to defeat Nazi planes and U-boats.
Percy Spencer and Raytheon went on to patent the new cooking technology, but it took them decades to figure out how to deliver the convenience of the microwave to the kitchen counter, and Raytheon had to purchase appliance maker Amana to finally make it a success. The first Amana microwaves honored the technology’s roots—they were called “Radarranges,” a brand Amana still uses, now with just a single “r” in the middle. Today, 96.4 percent of U.S. homes have a microwave oven—more homes than have a landline telephone or a computer—and a typical family of four goes through the equivalent of forty regular-size bags of microwave popcorn a year.19
When you use a microwave oven, to reheat coffee or puff a bag of popcorn, you’re really cooking with water—specifically with water molecules.
The microwave oven only cooks because of microwaves’ affinity for water at the molecular level. Microwave radiation—the same kind of radiation as radio waves or light waves—moves at a frequency that water molecules absorb. When you microwave a baked potato or a cardboard tray of frozen macaroni and cheese, it is the water molecules that get energized, and that do the cooking.
In fact, each individual water molecule is really a tiny magnet—the three joined atoms look a bit like Mickey Mouse’s head, two hydrogens as the big ears, one oxygen as the head. The hydrogen “ears” create a positive side, the single larger oxygen is the negative side. When microwaves come zinging through, each water molecule tries to orient itself in the waves of radiation, and ends up spinning. Water molecules inside a cup of coffee, or a baking potato, can spin 1 billion times a second in response to the microwaves.
The water molecules’ motion creates heat, which cooks the surrounding food. Microwave popcorn pops when the 14 percent of each kernel that is water vaporizes into steam, and expands to pop the kernel’s hull loose. (Conveniently, most plastics, dishes, and things like paper plates are transparent to microwave radiation, and a paper plate doesn’t contain many water molecules.)
Despite its sturdy simplicity, in fact, water is a complicated, unusual, almost enchanted substance—not in the emotional or cultural sense, but literally, physically, starting right at the molecular level, with the very magnetic quality that allows Percy Spencer’s “radar range” to work.
Scientists refer to molecules that are tiny magnets—one end with a small positive charge, one with a small negative charge—as polar molecules. In the case of water, the polarity has much more significance than making microwave popcorn possible.
