Bill Bryson - A short history of nearly everything

After you have left the troposphere the temperature soon warms up again, to about 40 degrees Fahrenheit, thanks to the absorptive effects of ozone (something else de Bort discovered on his daring 1902 ascent). It then plunges to as low as -130 degrees Fahrenheit in the mesosphere before skyrocketing to 2,700 degrees Fahrenheit or more in the aptly named but very erratic thermosphere, where temperatures can vary by a thousand degrees from day to night-though it must be said that “temperature” at such a height becomes a somewhat notional concept. Temperature is really just a measure of the activity of molecules. At sea level, air molecules are so thick that one molecule can move only the tiniest distance-about three-millionths of an inch, to be precise-before banging into another. Because trillions of molecules are constantly colliding, a lot of heat gets exchanged. But at the height of the thermosphere, at fifty miles or more, the air is so thin that any two molecules will be miles apart and hardly ever come in contact. So although each molecule is very warm, there are few interactions between them and thus little heat transference. This is good news for satellites and spaceships because if the exchange of heat were more efficient any man-made object orbiting at that level would burst into flame.

Even so, spaceships have to take care in the outer atmosphere, particularly on return trips to Earth, as the space shuttle Columbia demonstrated all too tragically in February 2003. Although the atmosphere is very thin, if a craft comes in at too steep an angle-more than about 6 degrees-or too swiftly it can strike enough molecules to generate drag of an exceedingly combustible nature. Conversely, if an incoming vehicle hit the thermosphere at too shallow an angle, it could well bounce back into space, like a pebble skipped across water.

But you needn’t venture to the edge of the atmosphere to be reminded of what hopelessly ground-hugging beings we are. As anyone who has spent time in a lofty city will know, you don’t have to rise too many thousands of feet from sea level before your body begins to protest. Even experienced mountaineers, with the benefits of fitness, training, and bottled oxygen, quickly become vulnerable at height to confusion, nausea, exhaustion, frostbite, hypothermia, migraine, loss of appetite, and a great many other stumbling dysfunctions. In a hundred emphatic ways the human body reminds its owner that it wasn’t designed to operate so far above sea level.

“Even under the most favorable circumstances,” the climber Peter Habeler has written of conditions atop Everest, “every step at that altitude demands a colossal effort of will. You must force yourself to make every movement, reach for every handhold. You are perpetually threatened by a leaden, deadly fatigue.” In The Other Side of Everest , the British mountaineer and filmmaker Matt Dickinson records how Howard Somervell, on a 1924 British expedition up Everest, “found himself choking to death after a piece of infected flesh came loose and blocked his windpipe.” With a supreme effort Somervell managed to cough up the obstruction. It turned out to be “the entire mucus lining of his larynx.”

Bodily distress is notorious above 25,000 feet-the area known to climbers as the Death Zone-but many people become severely debilitated, even dangerously ill, at heights of no more than 15,000 feet or so. Susceptibility has little to do with fitness. Grannies sometimes caper about in lofty situations while their fitter offspring are reduced to helpless, groaning heaps until conveyed to lower altitudes.

The absolute limit of human tolerance for continuous living appears to be about 5,500 meters, or 18,000 feet, but even people conditioned to living at altitude could not tolerate such heights for long. Frances Ashcroft, in Life at the Extremes , notes that there are Andean sulfur mines at 5,800 meters, but that the miners prefer to descend 460 meters each evening and climb back up the following day, rather than live continuously at that elevation. People who habitually live at altitude have often spent thousands of years developing disproportionately large chests and lungs, increasing their density of oxygen-bearing red blood cells by almost a third, though there are limits to how much thickening with red cells the blood supply can stand. Moreover, above 5,500 meters even the most well-adapted women cannot provide a growing fetus with enough oxygen to bring it to its full term.

In the 1780s when people began to make experimental balloon ascents in Europe, something that surprised them was how chilly it got as they rose. The temperature drops about 3 degrees Fahrenheit with every thousand feet you climb. Logic would seem to indicate that the closer you get to a source of heat, the warmer you would feel. Part of the explanation is that you are not really getting nearer the Sun in any meaningful sense. The Sun is ninety-three million miles away. To move a couple of thousand feet closer to it is like taking one step closer to a bushfire in Australia when you are standing in Ohio, and expecting to smell smoke. The answer again takes us back to the question of the density of molecules in the atmosphere. Sunlight energizes atoms. It increases the rate at which they jiggle and jounce, and in their enlivened state they crash into one another, releasing heat. When you feel the sun warm on your back on a summer’s day, it’s really excited atoms you feel. The higher you climb, the fewer molecules there are, and so the fewer collisions between them.

Air is deceptive stuff. Even at sea level, we tend to think of the air as being ethereal and all but weightless. In fact, it has plenty of bulk, and that bulk often exerts itself. As a marine scientist named Wyville Thomson wrote more than a century ago: “We sometimes find when we get up in the morning, by a rise of an inch in the barometer, that nearly half a ton has been quietly piled upon us during the night, but we experience no inconvenience, rather a feeling of exhilaration and buoyancy, since it requires a little less exertion to move our bodies in the denser medium.” The reason you don’t feel crushed under that extra half ton of pressure is the same reason your body would not be crushed deep beneath the sea: it is made mostly of incompressible fluids, which push back, equalizing the pressures within and without.

But get air in motion, as with a hurricane or even a stiff breeze, and you will quickly be reminded that it has very considerable mass. Altogether there are about 5,200 million million tons of air around us-25 million tons for every square mile of the planet-a not inconsequential volume. When you get millions of tons of atmosphere rushing past at thirty or forty miles an hour, it’s hardly a surprise that limbs snap and roof tiles go flying. As Anthony Smith notes, a typical weather front may consist of 750 million tons of cold air pinned beneath a billion tons of warmer air. Hardly a wonder that the result is at times meteorologically exciting.

Certainly there is no shortage of energy in the world above our heads. One thunderstorm, it has been calculated, can contain an amount of energy equivalent to four days’ use of electricity for the whole United States. In the right conditions, storm clouds can rise to heights of six to ten miles and contain updrafts and downdrafts of one hundred miles an hour. These are often side by side, which is why pilots don’t want to fly through them. In all, the internal turmoil particles within the cloud pick up electrical charges. For reasons not entirely understood the lighter particles tend to become positively charged and to be wafted by air currents to the top of the cloud. The heavier particles linger at the base, accumulating negative charges. These negatively charged particles have a powerful urge to rush to the positively charged Earth, and good luck to anything that gets in their way. A bolt of lightning travels at 270,000 miles an hour and can heat the air around it to a decidedly crisp 50,000 degrees Fahrenheit, several times hotter than the surface of the sun. At any one moment 1,800 thunderstorms are in progress around the globe-some 40,000 a day. Day and night across the planet every second about a hundred lightning bolts hit the ground. The sky is a lively place.