A Carol Highsmith photograph of one of the many wonders with gas at its core: the neon signage in downtown Reno, Nevada.

Library of Congress

Air Born

The discovery of gases led to both wonderful and terrible creations.

Sam Kean. Caesar’s Last Breath: Decoding the Secrets of the Air around Us. Little, Brown, 2017. 384 pp. $28.

“For you were made from dust, and to dust you will return.” No, wait, I’m sorry; I meant to say “gas”: for you were made from gas, and to gas you will return.

Compared with dust, being made from and returning to gas is a lot more exciting and certainly a much longer journey. In fact, we have gas to thank for everything around us, from the atoms that make up Earth, to the atmosphere that allows us to exist, to about half the food the world produces each year. “The story of Earth is the story of its gases,” writes Sam Kean, and he explores this story through his latest book, Caesar’s Last Breath: Decoding the Secrets of the Air around Us. And while some of the stories told in the book are about gases generally and not the atmosphere specifically, all are told in Kean’s winning voice and conversational style.

Let’s start at the very beginning (a very good place to start). About 4.5 billion years ago a supernova sent a shock wave through space. Part of this shock wave hit a cloud of mostly hydrogen gas and began to stir the pot, so to speak, and about 99.9% of that gas condensed into our sun. Most of the remaining gas formed Jupiter, Saturn, and the other gas giants, but some of it began clumping together a bit closer to the Sun and eventually condensed into the rocky planets, including Earth.

As Earth coalesced, it collected some extra gases that formed a flimsy atmosphere of hydrogen and helium, but that atmosphere was blasted away by solar wind. Fortunately, the molten Earth began to produce a new atmosphere as gases escaped from lava: water vapor, carbon dioxide, sulfurous compounds, even gaseous gold and mercury. That water vapor in the sky eventually condensed and began to rain back down, forming lakes and seas, which in turn absorbed some of the carbon dioxide from the atmosphere. We lost some gases and gained some gases every time an asteroid struck Earth, but asteroid strikes became fewer and further between. Eventually a crust formed on the surface of the planet, limiting the amount of escaping lava gases, and the atmosphere began to settle down into something that’s similar to the atmosphere we have today.

Even before humanity understood gases through the research of people like Joseph Priestley, Antoine Lavoisier, and Humphry Davy, we put the stuff to work for us in steam engines. Without gases we wouldn’t have anesthesia, refrigerators, or neon lights. Nitroglycerin and gun-powder work because, while exploding, they release a disproportionate number of gas molecules, which hurl outward at astounding speeds and destroy everything in their path. More constructively, by blowing air through molten iron you get steel for skyscrapers and automobiles.

One of the most famous stories of the atmosphere being put to good use is that of nitrogen fertilizer. We can thank volcanoes for the ample nitrogen in our atmosphere, but unfortunately the form of nitrogen they produce can’t be efficiently used by cells in living things. This is especially bad because nitrogen is the fourth most-abundant element in the human body, and relying on a handful of specialized bacteria to convert N2 to a form more useful to us is dicey at best. Theoretically, if you could mix the abundant N2 in the air with H2 split off from water molecules, you would get ammonia, a form of nitrogen that’s a powerful fertilizer. But the heat needed to produce the reactions would destroy any ammonia made.

Chemist Fritz Haber and chemical engineer Carl Bosch refused to let a small thing like impossibility deter them, and they found the right catalysts and a way to sufficiently pressurize the nitrogen and hydrogen gases to make ammonia production a reality. Today about half the world’s food is grown with the help of ammonia fertilizer, so it’s no stretch to say that converting atmospheric nitrogen has allowed the world population to reach numbers that would otherwise have been unattainable. Unfortunately, the work of Haber and Bosch also paved the way for gas warfare, which Kean discusses as well.

The story of our atmosphere isn’t just about what we take out of it, however, but also what we put in. Mushroom clouds carried radioactive fallout high into the atmosphere, where it was dispersed around the world by winds. By the 1960s radioactive atoms could be found in every square inch of Earth’s surface. The effects on the human body aren’t usually drastic (enough to shorten our lives by about 1.2 minutes on average, the same as four puffs of a cigarette), but we are still feeling them. For example, nuclear tests almost doubled the amount of carbon-14 (which forms radioactive CO2) in the air between 1950 and 1963, and levels still haven’t returned to normal. That extra carbon-14 is responsible for between a hundred thousand and one million additional DNA mutations per person per day, which have led to an estimated two million cancer deaths around the world that wouldn’t have occurred otherwise.

The industrial revolution changed our atmosphere extensively as well. Concentrations of CO2, methane, and nitrous oxide (three long-lived green-house gases) have increased significantly since 1750, as they can’t be filtered out of the atmosphere as quickly as we’ve put them in. And let’s not forget Thomas Midgley, who wins the award for most damage done to the atmosphere by a single person. Not only did Midgley invent some of the first chlorofluorocarbons (the infamous ozone destroyers) in the late 1920s, he also invented the tetraethyl lead additive used in gasoline, which pumped so much lead into the air that as many as 5,000 Americans died from lead-related heart disease each year before leaded gasoline began to be phased out in the mid-1970s.

From gas we came and ultimately to gas all will return when our Sun becomes a red giant and engulfs Earth. Humanity will be long gone by then, as the oceans will have boiled off and the planet turned into a molten hellscape unfit for life of any kind. The expanding Sun will vaporize whatever’s left and send our atoms and molecules back out into space. A lucky few may even find a use in a different corner of the galaxy someday.

The vast universe exists in each of us in miniature: our atoms were created in stars and deign to exist within us (for the time being). But let’s not forget we have the history of Earth within us as well. At any given moment you have probably just inhaled a molecule from the last breath Julius Caesar took as he lay dying at the Theater of Pompey. (Amazingly, the math checks out.) And think of this: the air circulating in your lungs right now, the blood coursing through your veins, contains molecules from just about any person who ever lived and from every event that ever happened. We are connected to everything that ever was: we are star stuff; we are Earth stuff.