Caesar’s Last Breath
title page of image Caesar’s Last Breath: The Epic Story of the Air Around Us

About the Author

SAM KEAN is the New York Times bestselling author of The Tale of the Duelling Neurosurgeons, The Disappearing Spoon and The Violinist’s Thumb, all of which were named Amazon’s top science books of the year. The Disappearing Spoon was a runner-up for the Royal Society’s book of the year for 2010, and The Violinist’s Thumb and The Tale of the Duelling Neurosurgeons were nominated for the PEN/E. O. Wilson award for literary science writing in 2013 and 2015, as well as the AAAS/Subaru prize. Sam’s work has appeared in The Best American Nature and Science Writing, the Atlantic Monthly, the New York Times magazine, Psychology Today, Slate, Mental Floss, and other publications.

About the Book

It’s invisible. It’s ever-present. Without it, you would die in minutes. And it has an epic story to tell.

In Caesar’s Last Breath, New York Times bestselling author Sam Kean takes us on a journey through the periodic table, around the globe, and across time to tell the story of the air we breathe, which, it turns out, is also the story of earth and our existence on it.

With every breath, you literally inhale the history of the world. On the Ides of March, 44 BC, Julius Caesar died of stab wounds on the Senate floor, but the story of his last breath is still unfolding; in fact, you’re probably inhaling some of it now. Of the sextillions of molecules entering or leaving your lungs at this moment, some might well bear traces of Cleopatra’s perfumes, German mustard gas, particles exhaled by dinosaurs or emitted by atomic bombs, even remnants of stardust from the universe’s creation.

Tracing the origins and ingredients of our atmosphere, Kean reveals how the alchemy of air reshaped our continents, steered human progress, powered revolutions and continues to influence everything we do. Along the way, we’ll swim with radioactive pigs, witness the most important chemical reactions humans have discovered, and join the crowd at the Moulin Rouge for some of the crudest performance art of all time. Lively, witty and filled with the astounding science of ordinary life, Caesar’s Last Breath illuminates the science stories swirling around us every second.


Like the molecules in a breath, so many individual pieces had to come together to make this book possible, and I once again marvel at how generous everyone was with their help. A few words on a page aren’t enough to express my gratitude, and if I’ve left anyone off this list, I remain thankful, if embarrassed.

For loved ones, I’d like to thank my dad for his love of science and of great lines, and my mom for her storytelling and for being a good sport. (I think I’ve teased her in every book so far.) Each year I feel a little luckier to know my siblings Ben and Becca, and it’s been a delight to watch my little niece and nephew, Penny and Harry, become real people. So much has changed with my friends in Washington, D.C., and South Dakota and elsewhere, but through marriages and moves and everything else, we’re all still sharing the good times.

Both my agent, Rick Broadhead, and my editor, John Parsley, saw how much potential this idea had, and helped me shape and refine the book throughout. Caesar’s Last Breath wouldn’t be here without them. I also want to thank everyone else in and around Little, Brown who worked with me on this book and others, including Malin von Euler-Hogan, Chris Jerome, Michael Noon, and Julie Ertl.

Finally, I offer a special thanks to the many, many brainy scientists and historians who contributed to individual chapters and passages, either by fleshing out stories, helping me hunt down information, or offering their time to explain something. They’re too numerous to list here, but rest assured that I haven’t forgotten your help …

Also by Sam Kean

The Tale of the Duelling Neurosurgeons

The Violinist’s Thumb

The Disappearing Spoon

Works Cited


Allaby, Michael. Atmosphere: A Scientific History of Air, Weather, and Climate. New York: Facts on File, 2009.

Almqvist, Ebbe. History of Industrial Gases. New York: Kluwer Academic/Plenum Publishers, 2003.

Canfield, Donald E. Oxygen: A Four Billion Year History. Princeton, NJ: Princeton University Press, 2014.

Fenster, Julie. Ether Day. New York: Harper Perennial, 2002.

Fisher, David. Much Ado about (Practically) Nothing: A History of the Noble Gases. New York: Oxford University Press, 2010.

Greenberg, Arthur. From Alchemy to Chemistry in Picture and Story. Hoboken, NJ: John Wiley & Sons, 2007.

Hazen, Robert M. The Story of Earth: The First 4.5 Billion Years, from Stardust to Living Planet. New York: Viking, 2012.

Jay, Mike. The Atmosphere of Heaven. New Haven, CT: Yale University Press, 2009.

Introduction: The Last Breath

Dando-Collins, Stephen. The Ides: Caesar’s Murder and the War for Rome. New York: John Wiley & Sons, 2010.

Goldsworthy, Adrian. Caesar: Life of a Colossus. New Haven, CT: Yale University Press, 2008.

Parenti, Michael. The Assassination of Julius Caesar. New York: The New Press, 2003.

Chapter One: Earth’s Early Air

Carson, Rob. Mount St. Helens. Seattle, WA: Sasquatch Books, 2000.

Findley, Rowe. “Mountain with a Death Wish,” National Geographic 159, no. 1 (1981):3–33.

Mastrolorenzo, Giuseppe et al. “Lethal Thermal Impact at Periphery of Pyroclastic Surges: Evidences at Pompeii,” PLoS ONE 5, no. 6 (June 2010): 1–12,

Rosen, Shirley. Truman of St. Helens. Seattle, WA: Madrona Publishers, 1981.

Stylianidis, Nearchos, Olorunfunmi Adefioye-Giwa, and Zane Thornley. “Complete Vaporisation of a Human Body,” Journal of Interdisciplinary Science Topics 2, no. 1 (2013): 1–4.

———. “Human Body Vaporisation,” Journal of Interdisciplinary Science Topics 2, no. 1 (2013): 1–3.

Zahnle, Kevin, Laura Schaefer, and Bruce Fegley. “Earth’s Earliest Atmospheres,” Cold Spring Harbor Perspectives in Biology 2, no. 10 (October 2010): 1–17.

Interlude: The Exploding Lake

Baxter, Peter J., M. Kapila, and D. Mfonfu. “Lake Nyos Disaster, Cameroon, 1986,” British Medical Journal 298, no. 5 (1989): 1437–1441.

Kling, George W. “The 1986 Lake Nyos Gas Disaster in Cameroon, West Africa,” Science 236, no. 4798 (1987): 169–175.

Krajick, Kevin. “Defusing Africa’s Killer Lakes,” Smithsonian 34, no. 6 (2003): 46–50.

Scarth, Alwyn. Vulcan’s Fury. New Haven, CT: Yale University Press, 1999.

Chapter Two: The Devil in the Air

Bown, Stephen. A Most Damnable Invention. New York: Thomas Dunne Books, 2005.

Craig, Peter. “Mankind in Peace, the Fatherland in War,” New Scientist 101, no. 1395 (1984):15–17.

Hager, Thomas. The Alchemy of Air. New York: Crown, 2008.

Interlude: Welding a Dangerous Weapon

Almqvist, Ebbe. History of Industrial Gases. New York: Kluwer Academic/Plenum Publishers, 2003.

Chapter Three: The Curse and Blessing of Oxygen

Bell, Madison Smartt. Lavoisier in the Year One. New York: W. W. Norton, 2010.

Bygrave, Stephen. “‘I Predict a Riot’: Joseph Priestley and Languages of Enlightenment in Birmingham in 1791,” Romanticism 18, no. 1 (2012): 70–88.

Malone, John. It Doesn’t Take a Rocket Scientist. New York: John Wiley & Sons, 2002.

Poirier, Jean-Pierre, and Rebecca Balinski. Lavoisier: Chemist, Biologist, Economist. Philadelphia: University of Pennsylvania Press, 1998.

Rose, R. B. “The Priestley Riots of 1791,” Past & Present 18, no. 1 (1960): 68–88.

Interlude: Hotter Than the Dickens

Haight, Gordon. “Dickens and Lewes on Spontaneous Combustion,” Nineteenth-Century Fiction 10, no. 1 (1955): 53–63.

Perkins, George. “Death by Spontaneous Combustion,” Dickensian 60, no. 342 (1964): 57.

West, John. “Spontaneous Combustion, Dickens, Lewes, and Lavoisier,” Physiology 9, no. 6 (1994): 276–278.

Chapter Four: The Wonder-Working Gas of Delight

Fenster, Julie. Ether Day. New York: Harper Perennial, 2002.

Holmes, Richard. The Age of Wonder. New York: Pantheon, 2009.

Jay, Mike. The Atmosphere of Heaven. New Haven, CT: Yale University Press, 2009.

Interlude: Le Pétomane

Moore, Alison. “The Spectacular Anus of Joseph Pujol,” French Cultural Studies 24, no. 1 (2013): 27–43.

Nohain, Jean, and F. Caradec. Le Pétomane. London: Souvenir Press, 1992.

Provine, Robert. Curious Behavior. Cambridge, MA: Harvard University Press, 2012.

Suarez, F. L., J. Springfield, and M. D. Levitt. “Identification of Gases Responsible for the Odour of Human Flatus and Evaluation of a Device Purported to Reduce this Odour,” Gut 43, no. 1 (1998): 100–104.

Suarez, F. L., J. K. Furne, J. Springfield, and M. D. Levitt. “Morning Breath Odor: Influence of Treatments on Sulfur Gases,” Journal of Dental Research 79, no. 10 (2000): 1773–1777.

Chapter Five: Controlled Chaos

Bown, Stephen. A Most Damnable Invention. New York: Thomas Dunne Books, 2005.

Marsden, Ben. Watt’s Perfect Engine. New York: Columbia University Press, 2004.

Interlude: Steeling Yourself for Tragedy

Bessemer, Henry. Sir Henry Bessemer, F.R.S.: An Autobiography. London: Offices of Engineering, 1905.

Jeans, William. The Creators of the Age of Steel. London: Chapman and Hall, 1973.

Lewis, Peter, and Ken Reynolds. “Forensic Engineering: A Reappraisal of the Tay Bridge Disaster,” Interdisciplinary Science Reviews 27, no. 4 (2002): 287–298.

Chapter Six: Into the Blue

Fisher, David. Much Ado about (Practically) Nothing: A History of the Noble Gases. New York: Oxford University Press, 2010.

Fontani, Marco, Mariagrazia Costa, and Mary Virginia Orna. The Lost Elements. New York: Oxford University Press, 2014.

Gillispie, Charles Coulston. The Montgolfier Brothers and the Invention of Aviation. Princeton, NJ: Princeton University Press, 1983.

Holmes, Richard. Falling Upwards: How We Took to the Air. New York: Pantheon, 2013.

Wolfenden, John. “The Noble Gases and the Periodic Table,” Journal of Chemical Education 46, no. 9 (1969): 569–575.

Interlude: Night Lights

Dewdney, Christopher. Acquainted with the Night. New York: Bloomsbury USA, 2008.

Ekirch, A. Roger. At Day’s Close: Night in Times Past. New York: W. W. Norton, 2006.

Tomory, Leslie. Progressive Enlightenment. Cambridge, MA: MIT Press, 2012.

Chapter Seven: The Fallout of Fallout

Boese, Alex. Electrified Sheep. New York: Thomas Dunne Books, 2012.

Mahaffey, James. Atomic Accidents. New York: Pegasus, 2015.

National Park Service, “The Archaeology of the Atomic Bomb,” Chapters One, Two, Three, and Five. Accessed November 4, 2015.

Rhodes, Richard. The Making of the Atomic Bomb. New York: Simon & Schuster, 1988.

Simon, Steven, André Bouville, and Charles Land. “Fallout from Nuclear Weapons Tests and Cancer Risks,” New Scientist 94, no. 1 (2006): 48–56.

Smith-Norris, Martha. “‘Only as Dust in the Face of the Wind’: An Analysis of the BRAVO Nuclear Incident in the Pacific, 1954,” Journal of American–East Asian Relations 6, no. 1 (1997): 1–34.

Welsome, Eileen. The Plutonium Files. New York: Dial Press, 1999.

Winkler, Allan. Life Under a Cloud. Champaign: University of Illinois Press, 1999.

Interlude: Albert Einstein and the People’s Fridge

Bryson, Bill. A Short History of Nearly Everything. New York: Broadway Books, 2004.

Dannen, Gene. “The Einstein-Szilard Refrigerators,” Scientific American 276, no. 1 (1997): 90–95.

Illy, József. The Practical Einstein. Baltimore: Johns Hopkins University Press, 2013.

Trainer, Matthew. “Albert Einstein’s Patents,” World Patent Information 28, no. 2 (2006):159–165.

Chapter Eight: Weather Wars

Fleming, James R. “The Climate Engineers,” Wilson Quarterly (Spring 2007): 46–60.

Gleick, James. Chaos. New York: Penguin, 1987.

Langmuir, Irving. “Control of Precipitation from Cumulus Clouds by Various Seeding Techniques,” Science 112, no. 2898 (1950): 35–41.

Lorenz, Edward. The Essence of Chaos. Seattle: University of Washington Press, 1995.

Interlude: Rumbles from Roswell

McAndrew, James. “The Roswell Report,” Air Force Historical Studies Division, 1995. Accessed November 4, 2015.

Muller, Richard. Physics for Future Presidents. New York: W. W. Norton, 2009.

Pretor-Pinney, Gavin. The Wave Watcher’s Companion. New York: Penguin, 2011.

Chapter Nine: Putting on Alien Airs

Bennett, Jeffrey. Beyond UFOs. Princeton, NJ: Princeton University Press, 2010.

Kasting, James, and David Catling. “Evolution of a Habitable Planet,” Annual Review of Astronomy and Astrophysics 41, no.1 (2003): 429–463.


Earth’s Early Air

Sulfur dioxide (SO2)—currently 0.00001 parts per million in the air; you inhale 120 billion molecules every time you breathe
Sulfur dioxide (SO2)—currently 0.00001 parts per million in the air; you inhale 120 billion molecules every time you breathe
Hydrogen sulfide (H2S)—currently 0.000005 parts per million; you inhale 60 billion molecules every time you breathe
Hydrogen sulfide (H2S)—currently 0.000005 parts per million; you inhale 60 billion molecules every time you breathe

Fear of being murdered first drove Harry Truman into hiding in the foothills of Mount Saint Helens in 1926. Not that Harry Truman, although this one—Harry Randall Truman—did appreciate his namesake. “He’s a gutsy old codger,” said Truman of Truman. “Bet he’ll go down as one of the greatest goddamn presidents.” This Truman would know a thing or two about being a gutsy old codger. After fleeing to Washington State at age thirty, he stuck out fifty-four years of brutal, isolating winters under the glare of Mount Saint Helens. And even when the mountain began to steam and snort and bellow in the spring of 1980, it couldn’t dislodge him except in the most spectacular way possible—by blowing him straight up into the atmosphere.

Truman’s family of loggers had moved to Washington State during his childhood, and after he graduated from high school he enlisted in the army, serving as an airplane mechanic during World War I. (A born raconteur, Truman would later claim that he flew combat missions overseas, his white scarf streaming behind him in the open cockpits of the day.) Back home he married a sawmill owner’s daughter and became a car mechanic, but he found both marriage and regular employment tedious. He tried prospecting for gold instead and found it worse than tedious, an outright pain in the ass.

So when Prohibition descended, he started bootlegging, a job more suited to his temperament. Playing fast and loose with the law tickled him, and he liked the quick cash. He also enjoyed a drink now and then, and didn’t appreciate a gaggle of do-gooders lecturing him on the evils of whiskey. Eventually he partnered with some gangsters in Northern California and started running hooch up the coast, supplying whorehouses and speakeasies along the way. He was having a great goddamn time of it all, but in 1926, something spooked him. He never quite said what. Perhaps he got too friendly with someone’s special lady or tried to horn in on some mobster’s territory. Regardless, he started carrying a submachine gun around.

One day he finally grabbed his wife and daughter and fled to the forests around Mount Saint Helens to lie low.

Motormouth Harry Randall Truman, drinking a glass of “panther pee,” at his beloved lodge in the shadow of Mount St. Helens. (Photo courtesy U.S. Forest Service)
Motormouth Harry Randall Truman, drinking a glass of “panther pee,” at his beloved lodge in the shadow of Mount St. Helens. (Photo courtesy U.S. Forest Service)

To make do he began managing a gas station and grocery store three miles north of the summit; he gradually expanded that into a campground with cabins and boats to rent. It proved a popular location. Gorgeous fir trees, some 250 feet tall and eight feet in diameter, ringed his house. The campgrounds also contained Spirit Lake, a 2.5-mile-long slip of water as cold and clear as chilled gin. Given the remoteness, Truman could keep on bootlegging as well, and he stashed several barrels of homemade whiskey—which he labeled “Panther Pee”—around the forest.

His wife, meanwhile, found the isolation grating. Nor did she appreciate being separated from their daughter, who attended boarding school several miles distant. Perhaps inevitably, Truman and his wife divorced in the early 1930s. Truman quickly remarried in 1935, but the second Mrs. Truman—every bit as pissy and vine-gary as Truman himself—didn’t last much longer. (It didn’t help that Truman tried to “win” arguments with her by tossing her into Spirit Lake. She couldn’t swim.) So Harry tried again, first wooing another local girl and then switching allegiance to her sister, Edna. Not exactly a romantic start, but once he fell in love with Eddie, Truman never quite got the barb out of his heart.

Eddie must have loved him something fierce, too, because Truman didn’t sound like the easiest husband. Most dawns, while he attended to chores, she had to rise early to whip up his favorite breakfast: scrambled cow brains with a glass of buttermilk to wash them down. “This will keep a man vi-i-irile,” he’d cackle. Eddie also had to put up with his mouth. Because he spoke quickly, people sometimes had trouble understanding Truman, but you could always pick out the cuss words. Friends were “old bastards,” while people he knew less well were “stupid sons of bitches.” (He once drove Supreme Court justice William Douglas off his property for looking like a sissy, although they later became friends.) Truman could be a know-it-all, too. Whenever a photographer visited to snap a few pictures of Mount Saint H, Truman would butt in. “You gotta put a human being in the goddamn thing,” he’d complain. “A little human interest is what means so much to the goddamn public.” Listening to interviews decades later, after Truman became famous, you’d think his favorite word was beep.

After a good day of renting out boats on Spirit Lake, Truman might take in $1,500 in cash. He’d find Eddie in the café they ran together and hand over the money, then pour himself a tall glass of his favorite panther pee—Schenley whiskey cut with Coke—and shoot the shit with his guests. As a couple they sometimes splurged on things like Harry’s pink 1956 Cadillac, which wasn’t exactly practical on the mountain roads but which he loved almost half as much as he loved Eddie. More often, though, they plowed the money back into the campgrounds or café. Or they saved it for the lean months, those winters when nine feet of snow fell and money got, as guess who said, “tighter than a bull’s ass at fly time.” But even then, Truman couldn’t help but marvel at his luck, living where he did. “Look at that!” he’d say, pointing at Mount Saint Helens. “You’ll never see anything more beautiful in the whole goddamn world than that old mountain.”

However correct the sentiment—Mount Saint Helens was indeed beautiful, the platonic ideal of snow-capped mountainness—this was actually bad geology on Truman’s part, since the cone of Mount Saint Helens wasn’t old at all; it barely existed in Julius Caesar’s day. It might seem impossible for thousands of feet of mountain to rise in just a few thousand years, but Mount Saint Helens was an active volcano, and active volcanoes can add height quickly by packing lava onto their slopes. In fact, although Fire Mountain (as local Indians called it) hadn’t erupted since 1857, even an amateur could spot evidence of past eruptions all around, such as hiking trails peppered with old ash, and volcanic pumice stones so porous that, when tossed into Spirit Lake, they floated. Every so often visitors would feel a tremor, too. But for Truman, the danger only added to the mountain’s allure.

Truman had been living in the shadow of Mount Saint Helens for nearly fifty years when everything unraveled. One night in September 1975, Eddie felt ill and retired to bed early. Truman had friends visiting from town that night, and he telephoned them to bring up a bottle of Schenley for himself and a surprise gift for Eddie, a plant, to cheer her up. When the plant arrived, he brought it straight up to their room—and came racing back down the stairs moments later. He was talking even faster than normal, verging on incoherence. “Eddie’s sick! Eddie’s sick!” was all they could make out. In fact, Eddie had already died of a heart attack. But for another hour he kept begging people to help her.

Eddie’s death opened up a sinkhole inside Truman. Smiles came only grudgingly afterward, and friends who’d always laughed at how spry and fit he seemed—“tougher than boiled owl,” one called him—now remarked on how run-down he looked, showing every one of his seventy-nine years. During the summers he at least had the campground to distract himself. But people worried about him during those six-month-long winters, when for weeks at a stretch he might have no other companion than Mount Saint Helens—two lonely, solitary figures staring at each other across miles of forest.

That isolation was about to end, however. Around the time Eddie died, a few government geologists who had been sampling layers of rock around Mount Saint Helens announced that they’d discovered a grim record of eruptions in its past. A report they released in 1978 went even further, describing the mountain as “more active and more explosive during the last 4,500 years than any other volcano in the contiguous United States.” Prophetic words. In nature, beautiful often means deadly, and that beautiful mountain cone might as well have been a cannon barrel.

Mount Saint Helens was the greatest geology lesson in American history. It also provided, believe it or not, a fascinating peek at the early days of our planet and the creation of our atmosphere. We don’t usually think about air as being created—it seems like it just is—but all planets have to manufacture their atmospheres from scratch. And despite how nasty volcanic fumes might seem, they supplied the basic ingredients on Earth. Understanding our air, then, requires understanding these explosions of lava and gas—and there’s no better place to start than the most scrutinized eruption in history and the unlikely hero who helped make it famous.


You can trace the danger lurking beneath Mount Saint Helens to the very early days of planet Earth. Around 4.5 billion years ago, a supernova detonated in our neck of the cosmos and sent a shock wave into space. This shock wave plowed into a sea of mostly hydrogen gas that happened to be nearby and stirred something inside it to life, causing the sea to grow choppy and swirl in a vortex about its center. Gravity eventually sucked together 99.9 percent of that gas to form a new star, our sun. The majority of the remaining gas got pushed to the edges of this incipient solar system, where it formed gas giant planets like Jupiter and Saturn.

Meanwhile, a small amount of gas got stranded in between the sun and the gas giants, and the elements within this cloud—oxygen, carbon, silicon, iron, and others—began clumping together on their own, first into microscopic specks, then into boulders and asteroids, then continent-sized rocks. Gravity being an efficient janitor, this sweeping together of small bits into large masses happened quickly—a million years by some accounts. When enough pieces had bonded, several rocky planets emerged, including Earth. Everything around you, then, no matter how solid it seems—the floor beneath your feet, the book you’re holding, even your body—all started off as a gas. You are an ex-gas.

Although it might sound dubious to talk about a solid body like Earth as an erstwhile gas, it makes sense if you examine what solids and gases fundamentally are. The molecules in a solid have a fixed address and cannot shift around much; that’s why solids retain their shape so well. In liquids, the molecules still touch and rub together, but they have more energy and more freedom to slide about, which explains why liquids flow and take the shape of their containers. Gas molecules don’t rub elbows at all; they’re feral, with much more space between neighbors. And when gas molecules do meet, they crash together and rebound in new directions, like a chaotic game of 3-D billiards. An average molecule of air at 72°F zips around at a thousand miles per hour.

On some level, then, solids and liquids and gases seem entirely different—and early scientists in fact classified things like water, ice, and steam as distinct substances. Today we know that’s not true. Heat up solid ice, and its molecules snap their chains and start to slide around like a liquid. Pump still more heat energy in, and the liquid molecules leap into the air and become a gas. It’s all the same substance, just in a different guise. And other materials can undergo this transformation as well. We’re not used to thinking about, say, the iron or silicon or uranium inside rocks as potential vapors, but every last substance on the periodic table can become a gas if hot enough. The reverse process works as well. Withdraw heat from a gas, and it will dew into a liquid. Subtract more heat, and a solid forms. Increasing the pressure on a gas can also crush its molecules into less sprightly states of matter.

These different states of matter mingled uneasily on the early Earth—a seething, molten mass that looked nothing like the manicured planet we know today. After (solid) space rocks began clumping together to form a planet initially, the immense gravitational pressures involved melted most of them into liquids. Denser liquids (such as molten iron) sank into the core, while lighter ones rose—only to resolidify at the surface when they encountered the cold sting of outer space. Overall this Earth resembled an egg, with a mostly iron yolk, a gooey mantle surrounding it, and a thin black shell of rock. The big difference was that this shell was fractured into millions of pieces, with molten lava leaking out between the cracks. Darkness never quite descended at night on the early Earth because of this lava’s orange glow, and not infrequently a spume of it would leap into the air, like the garden fountains in hell.

This early Earth did have an atmosphere (atmosphere number one, for those keeping track), but it was so wispy it hardly deserved the name. It consisted mostly of hydrogen and helium that had been stranded between the sun and Jupiter. And not long after it formed, this atmosphere disappeared on us, as the solar wind—a nor’easter of protons and electrons that originate inside the sun—swept these gases away from Earth and into space. Many of these gas atoms escaped of their own accord as well. One law of gases says that small molecules move at much higher speeds than large, stodgy molecules. Hydrogen and helium sit atop the periodic table as the lightest and therefore swiftest elements, and every day a certain fraction of them would exceed the escape velocity of Earth (seven miles per second). Like trillions of tiny Saturn rockets they’d then bid our Hadean hellscape goodbye for the frozen calm of outer space.

A second atmosphere soon arose in place of the first one, an atmosphere summoned from the very ground itself. Just as there’s oxygen dissolved in blood and carbon dioxide in champagne, magma (underground lava) has gases dissolved in it. And just as carbon dioxide whooshes out of open bottles, this magma would vent those gases when it reached a crack in Earth’s surface and the pressure on the magma suddenly dropped. These escaping gases probably (geologists bicker about this) consisted mostly of water vapor and carbon dioxide, but other gases poured out as well. If you’ve ever stood near a volcanic rift, you can probably guess some of them, like the sulfurous compounds that give rotten eggs and gunpowder their bouquets (hydrogen sulfide and sulfur dioxide, respectively). The vents also released a faint haze of hot metallic vapors, including gold and mercury atoms. All fun stuff to breathe.

Some geologists have argued that all these gases came rushing out of the ground at once—the so-called Big Burp. Sadly for the juvenile-minded everywhere, the Big Burp probably never happened: Earth seems to have hoarded her gases instead, letting them seep out. Not that a gradual release made things more hospitable. The steam still would have scalded your skin, the sulfur gases still would have raked your nose, the acids and ammonia still would have shredded your lungs. The pressures involved weren’t pleasant, either. Magma back then was far fizzier, having a much higher concentration of gases, and billions of tons of gases got released each day. The resulting air pressure, perhaps one hundred times modern levels, would have imploded your skull and crushed you into a much more spherical version of yourself. The slightest breeze in air this dense would have bowled you over and sent you tumbling into a pool of magma.

This second atmosphere isn’t the same ocean of air we live under today, for a few reasons. The major component of air back then, steam, eventually condensed out as rain and began to pool on the ground in lakes and seas. The formation of seas and lakes also had knock-on effects, because the second-most-common ingredient in air then, carbon dioxide, dissolves readily in water and reacts with minerals there to form solid precipitates. This removes the CO2 from circulation.

Another reason we don’t live under thousands of pounds of pressure today is that stray asteroids (and/or comets) kept slamming into us and blasting that early air back into space. Not every impact was a disaster, mind you. Smaller asteroids probably even added gases to our atmosphere, from vapors trapped inside them. But every time our planet landed a big one, it learned a hard lesson about conservation of energy. Much of the kinetic energy of the asteroid’s motion got transformed into heat when it struck home, heat that boiled atmospheric gases away into space. The rest of the kinetic energy created a gigantic shock wave that swept even more air up and away. Some geologists argue that impacts like these stripped our atmosphere bare multiple times, completely denuding us. If that’s true, then instead of referring to our volcano-born atmosphere as the second atmosphere, we should probably talk about atmospheres 2a, 2b, 2c, and so on. Each one had the same mix of gases, but asteroids and comets kept evacuating them.

One of these evacuations deserves special attention, since it also created our moon. It’s actually a strange moon, ours. Every other mooned planet we know of has mere gnats circling it, bodies far less massive; we have an albatross, a body one-quarter our size. To explain that anomaly, astronomers in the twentieth century devised several theories. Some argued that our moon formed independently, as a separate planet, and that we snared it in our gravitational mitt one day as it tried to slip past. Others, taking up a suggestion by Charles Darwin’s son, astronomer George Darwin, argued that the moon somehow fissioned off from Earth in its not-quite-solid days, like a daughter cell budding off from a parent.

Moon rocks gathered in 1969 finally settled the issue, pointing to a combination of these theories. Among other clues, moon rocks had fewer volatile gases trapped inside them than Earth rocks, implying that something had boiled the lunar gases off. Boiling away all the gases inside a body as big as the moon, however, would have required massive amounts of heat, which suggests an unthinkably large collision: when astronomers ran the numbers, they found that this hypothetical impactor—now called Theia—was roughly as big as Mars. Theia likely formed as a separate planet at a different point on Earth’s orbit, a few months “behind” or “ahead” of us as we circled the sun. But gravity, that eternal meddler, couldn’t abide two planets circling in the same vicinity, and within about fifty million years of their formation decided to bang them together like rocks. Astronomers call it the Big Thwack.

If you’re thinking here of the asteroid impact that wiped out the dinosaurs, think again. That strike produced pillars of fire right out of Exodus, sure, and threw up enough dust to dim the sun for several years. But Earth as a whole barely flinched: even after the sparrow cracked the windshield, the car kept going. Theia was more like plowing into a moose—major structural damage. The collision not only ejected our atmosphere, it may well have boiled our frickin’ oceans and vaporized whole continents of rock. It also plowed deep into our mantle and left Earth lopsided, as if someone had punched a desk globe. Theia itself vaporized, and most of the gaseous remains began to stream into space and swirl around us, creating our very own celestial ring. But unlike the rings of Saturn, which are mostly ice and rocks, this piping-hot gas ring eventually cooled and coalesced into our moon.

In the long run Theia’s impact gave us all sorts of poetic things, like full moons and even spring and autumn, since it nudged Earth sideways off its up-and-down axis and allowed for the variable sunlight that gives rise to seasons. In the short term, though, Theia managed to make our planet even less hospitable than before. In particular, we got an atmosphere even hotter and nastier than the volcanic atmosphere that preceded it. This atmosphere, which lasted for perhaps a thousand years, consisted mostly of scorching hot silicon (think vaporized sand) punctured by iron “rain.” It would have had a salty tang as well, from fumes of sodium chloride; imagine every breath tasting like a salt lick.

Our new moon watched over all this from a height of just 15,000 miles; it loomed in the sky a dozen times larger than the sun does today. And its fiery, molten state would have left it glowing like a blackened, bloodshot eye. There might still have been poetry in this moon, but it was more Dante than Frost.

Eventually the solar system ran low on asteroids to shell Earth with (regularly, anyway). As a result, any gases that accumulated in our atmosphere could stick around instead of being blasted away into space. Just as important, proper volcanoes emerged. Volcanoes probably weren’t common on the very early Earth, because the magma could vent its gases more easily through cracks in the semi-molten outer shell. But when space rocks stopped hitting us, our planet cooled and acquired a hard surface crust with far fewer cracks; magma began collecting in underground pools instead. Because that magma still contained dissolved gases, the pressure inside those pools often swelled to dangerous levels. Over time, the pressure would grow so high that lava and hot gases would burst through the overlying rock and scorch everything in their path.

Although magma today is far less fizzy than it used to be, this billennia-old cycle of pressure building up underground and then exploding upward continues today. In fact, it’s exactly what happened with Mount Saint Helens in 1980.


Eddie’s death depleted Truman. Days and weeks slipped by in lethargy, and he grew distracted and negligent at work. A tree he felled clobbered him on the head. He got his hand caught in a snowblower. He knocked himself unconscious falling off his porch and woke up in the snow in his tighty-whities. The campground suffered, too. Without Eddie to make up beds for guests, the cabins looked slovenly. Truman also flamed out as a cook. Eddie had never exactly earned a Michelin star at the café; among other delicacies, she served hot-dog sandwiches and hamburgers on soggy white bread. But Truman left diners with culinary PTSD. Lunch might be PB&O—that’s peanut butter ’n’ onions—while dinner might consist of “chicken back soup,” a bird carcass boiled with twenty-five cloves of garlic. You almost wonder whether he was trying to drive customers away.

If Truman felt dispirited, though, the mountain looming over him grew more and more feisty each month, thanks to shifts in the continental plates beneath it. By 1980 the terms “continental drift” and “plate tectonics” were just starting to feel comfortable in the mouths of geologists—a situation that few of them could have predicted even fifteen years earlier. The first person to propose the theory of continental drift was German meteorologist Alfred Wegener, who spent the early 1900s puzzling over the fact that the edges of South America and Africa seemed to fit together like broken fragments of pottery. He noticed that the two continents shared similar fossil patterns as well, and after getting shot in the throat during World War I, he decided to spend his convalescence writing a book in which he proposed that the continents rested on large plates that had somehow drifted over time.

To say that geologists didn’t embrace Wegener’s theory is a bit like saying that General Sherman didn’t receive the warmest welcome in Atlanta. Geologists loathed plate tectonics, even got pleasure out of loathing it. But as more and more evidence trickled in through the 1940s and 1950s, the drifting of continental plates didn’t seem so silly anymore. The balance finally tipped in the late 1960s, and in one of the most stunning reversals in science history, pretty much every geologist on earth had accepted Wegener’s ideas by 1980. The rout was so complete that nowadays we have a hard time appreciating the theory’s importance. In the same way that the theory of natural selection shored up biology, plate tectonics took a hodgepodge of facts about earthquakes, mountains, volcanoes, and the atmosphere, and fused them together into one overarching schema.

Continental plates can sometimes shift all at once in dramatic fashion, jolts we call earthquakes. Much more commonly the plates slowly grind past one another moving at about the rate that fingernails grow. (Think about that next time you clip your nails: we’re that much closer to the Big One.) When one plate slips beneath the other, a process called subduction, the friction of this grinding produces heat, which melts the lower plate and reduces it to magma. Some of this magma disappears into the bowels of Earth; but the lighter fraction of it actually climbs back upward through random cracks in the crust, swimming toward the surface. (That’s why hunks of pumice, a volcanic rock, float when tossed into water, because pumice comes from material with such a low density.) The heat of grinding also liberates carbon dioxide from the melting plate, as well as lesser amounts of hydrogen sulfide, sulfur dioxide, and other gases, including trace amounts of nitrogen.

Meanwhile, as hot magma pushes upward through cracks in the crust, water in the crust seeps downward through those same cracks. And here’s where things get dangerous. One key fact about gases—it comes up over and over—is that they expand when they get warmer. Related to this, the gaseous version of a substance always takes up far more space than the liquid or solid version. So when that liquid water dribbling downward meets that magma bubbling upward, the water flashes into steam and expands with supernoval force, suddenly occupying 1,700 times more volume than before. Firefighters have special reason to fear this phenomenon: when they splash cold water onto hot, hissing fires, the burst of steam in an enclosed space can flash-burn them. So it goes with volcanoes. We ogle the orange lava pouring down the slopes, but it’s gases that cause the explosions and that do most of the damage.

Around the world roughly six hundred volcanoes are active at any moment. Most of them lie along the famous Ring of Fire around the Pacific Ocean, which rests atop several unstable plates. In the case of Mount Saint Helens, the Juan de Fuca plate off Washington State is grinding away against the North American plate, and doing so roughly a hundred miles beneath the surface. This depth leaves a heavy cap of rock over the pools of magma and thereby prevents constant venting of noxious fumes. But when one of these deep pockets does pop, there’s that much more shrapnel.


On March 20, 1980, a 4.0-magnitude tremor shook Mount Saint Helens. Feeling the ground shudder wasn’t unusual in those parts, but unlike with previous earthquakes, this time the ground kept jiggling. In a typical five-year span, Mount Saint Helens might experience forty quakes. In the week after March 20, it got rocked by one hundred.

This put scientists in a delicate position. They didn’t want to alarm the public about an eruption that might never happen. Just five years earlier a doomsday prediction about the Mount Baker volcano north of Seattle had fizzled, making geologists look foolish. Still, Mount Saint Helens wouldn’t simmer down. On March 27 a plume of smoke broke through the peak, rising 7,000 feet and staining the white snow there black. Shortly afterward state officials closed all roads around Mount Saint Helens with barricades. More controversially, they began forcibly evacuating residents. A young, blond geologist named David Johnston explained the reasoning to reporters: “This is like standing next to a dynamite keg. The fuse is lit, but you don’t know how long the fuse is.”

One resident in the evacuation zone, however, decided that the government didn’t know what the hell it was talking about. Harry Truman, just three miles distant from that beautiful, deadly cone, dismissed the first quake as a mere avalanche. Even during the onslaught of aftershocks, he refused to believe he was in danger. He’d lived most of his life in the mountain’s shadow, including his best years, with Eddie, and he declared that “if the mountain did do something, I’d rather go right here with it.”

Word spread fast about The Man Who Wouldn’t Leave the Mountain, especially among reporters, who were finding the volcano beat frustrating. Aside from Johnston’s “dynamite keg” quote, reporters looking for hard facts couldn’t get much out of geologists, who hedged every prediction and then hedged the hedges. So most stories went the other way, brushing over the science and emphasizing local color. As Truman used to say to photographers, you need a goddamn human in the thing to keep people interested, and his crotchety old man routine—he even wore socks with sandals sometimes—played well in the media. For decades Truman had actually shied away from publicity, still spooked that someone from his bootlegging days might show up and smoke him. But hell, by 1980 that was half a century ago, and Truman discovered that he liked telling old stories to fresh ears. Like that time he fought off a bear with a rake, clad only in his underwear. Or the time he ginned up a local sasquatch legend by whittling two big wooden feet and leaving footprints in the snow. He also dusted off several World War I stories, and claimed that he had half a mind to strap on his old pilot’s helmet and drop a bomb into the crater to shut it up.

Beyond telling stories, Truman bad-mouthed local officials every chance he got. “They say she’s gonna blow again, but they’re lying like horses trot,” he sneered. He also boasted that he could judge the Richter strength of an earthquake faster than geologists could, just by watching how far the Rainier Beer sign in the café window swung side to side. Every major media outlet in the country came a-calling at some point, and every reporter knew to bring some Schenley whiskey as an offering. Truman soon had a cabinet full of bottles, and he hooted that the mountain could do its worst now—he could wait out anything.

Officials considered arresting Truman to enforce the evacuation order and clamp down on the hoopla. But what then? Throwing an old man in jail wouldn’t exactly win the public over, and good luck finding a jury to convict. Better to let him spout off, even in the New York Times and National Geographic.

For the public, every week that passed without an explosion ratcheted up the tension and excitement. Yard signs in local communities read “St. Helens: keep your ash off my lawn.” Given all the logging trails around the mountain, anyone with a decent map could circumvent the roadblocks, and people practically began having picnics on the slopes, thrilled at the prospect of seeing some real-life lava. Even Washington’s governor, Dixy Lee Ray—who as a former scientist (a marine biologist) really should have known better—got swept up. “I’ve always said,” she gushed, “that I hoped to live long enough to see one of our volcanoes erupt.” At a low point in the hijinks, a Seattle film crew helicoptered in and filmed a beer commercial near the peak.

All the while, gases kept building up inside Mount Saint Helens. Planes circling overhead detected stronger and stronger whiffs of sulfur dioxide (the gunpowder smell), which meant that sulfur-rich magma was rising toward the surface. (Flying above the mountain was technically illegal at this point, but so many planes violated the ban that one pilot compared the swarm to an old-fashioned dog-fight.) More ominously, in mid-April geologists noticed a tumor on the mountain’s north side, a huge blister of bulging rock. No one knew how fast the bulge was growing, so planes went up with surveying equipment that had lasers capable of detecting a rise of even a few millimeters per day. A few millimeters doesn’t sound that dramatic, until you realize that you’re talking about lifting an entire mountain face. Turns out they didn’t need such fine resolution anyway: the bulge was growing five feet taller every day. Government geologists had seen enough bad signs that on May 9 they pulled back their observation towers to a distance of six miles, well beyond the calculated danger zone. Truman chuckled at the scaredy-cats.

At least he did so publicly; privately, the pressure was building up inside him, too. Truman had always argued that the huge fir trees that stood between him and the volcano would buffer and protect him, but as the weeks wore on, friends could see his conviction faltering. He was more alone than ever, and although reporters laughed at his claims of wearing spurs to bed, to keep him from being bucked onto the floor, he was only half joking. Some nights the tremors would rattle the café dishes several times an hour, keeping him on edge. On the nights he did manage to fall asleep, he might wake up to find his bed pushed across the room. He didn’t want to abandon his and Eddie’s home, but that didn’t mean he wanted to live each night in terror.

Sensing this, friends and officials made one last effort in mid-May to coax the wildcat down the mountain. Truman said no. He did so in part because by that point he was receiving sacks full of mail from people inspired by his courage. Marriage proposals trickled in, too. (“Now, why would some eighteen-year-old chick want to marry an old [beep] like me?” he marveled.) He also got a letter from Dixy Lee Ray praising his steadfastness, which he practically waved over his head in excitement. It’s hard to say whether the fame and adulation reinforced what he wanted to do anyway, or whether the pressure of being famous forced him into decisions he wouldn’t otherwise have made. Either way, he wasn’t going anywhere.

Giving up on Truman, state officials decided to clear everything else off the mountain. After three days of seismic peace, they even lifted the blockade for local cabin owners on May 17, allowing them to dash up the roads in empty trucks and pack up chairs, tables, toasters, cameras, and whatever else they could grab. Officials gave permission for a second run the next morning. The mountain had other plans.