A Short History of Nearly Everything
Page 26
Haldane's son Jack, known to posterity as J.B.S., was a remarkable prodigy who took an interest in his father's work almost from infancy. At the age of three he was overheard demanding peevishly of his father, "But is it oxyhaemoglobin or carboxyhaemoglobin?" Throughout his youth, the young Haldane helped his father with experiments. By the time he was a teenager, the two often tested gases and gas masks together, taking turns to see how long it took them to pass out.
Though J. B. S. Haldane never took a degree in science (he studied classics at Oxford), he became a brilliant scientist in his own right, mostly in Cambridge. The biologist Peter Medawar, who spent his life around mental Olympians, called him "the cleverest man I ever knew." Huxley likewise parodied the younger Haldane in his novel Antic Hay , but also used his ideas on genetic manipulation of humans as the basis for the plot of Brave New World . Among many other achievements, Haldane played a central role in marrying Darwinian principles of evolution to the genetic work of Gregor Mendel to produce what is known to geneticists as the Modern Synthesis.
Perhaps uniquely among human beings, the younger Haldane found World War I "a very enjoyable experience" and freely admitted that he "enjoyed the opportunity of killing people." He was himself wounded twice. After the war he became a successful popularizer of science and wrote twenty-three books (as well as over four hundred scientific papers). His books are still thoroughly readable and instructive, though not always easy to find. He also became an enthusiastic Marxist. It has been suggested, not altogether cynically, that this was out of a purely contrarian instinct, and that if he had been born in the Soviet Union he would have been a passionate monarchist. At all events, most of his articles first appeared in the Communist Daily Worker .
Whereas his father's principal interests concerned miners and poisoning, the younger Haldane became obsessed with saving submariners and divers from the unpleasant consequences of their work. With Admiralty funding he acquired a decompression chamber that he called the "pressure pot." This was a metal cylinder into which three people at a time could be sealed and subjected to tests of various types, all painful and nearly all dangerous. Volunteers might be required to sit in ice water while breathing "aberrant atmosphere" or subjected to rapid changes of pressurization. In one experiment, Haldane simulated a dangerously hasty ascent to see what would happen. What happened was that the dental fillings in his teeth exploded. "Almost every experiment," Norton writes, "ended with someone having a seizure, bleeding, or vomiting." The chamber was virtually soundproof, so the only way for occupants to signal unhappiness or distress was to tap insistently on the chamber wall or to hold up notes to a small window.
On another occasion, while poisoning himself with elevated levels of oxygen, Haldane had a fit so severe that he crushed several vertebrae. Collapsed lungs were a routine hazard. Perforated eardrums were quite common, but, as Haldane reassuringly noted in one of his essays, "the drum generally heals up; and if a hole remains in it, although one is somewhat deaf, one can blow tobacco smoke out of the ear in question, which is a social accomplishment."
What was extraordinary about this was not that Haldane was willing to subject himself to such risk and discomfort in the pursuit of science, but that he had no trouble talking colleagues and loved ones into climbing into the chamber, too. Sent on a simulated descent, his wife once had a fit that lasted thirteen minutes. When at last she stopped bouncing across the floor, she was helped to her feet and sent home to cook dinner. Haldane happily employed whoever happened to be around, including on one memorable occasion a former prime minister of Spain, Juan Negrín. Dr. Negrín complained afterward of minor tingling and "a curious velvety sensation on the lips" but otherwise seems to have escaped unharmed. He may have considered himself very lucky. A similar experiment with oxygen deprivation left Haldane without feeling in his buttocks and lower spine for six years.
Among Haldane's many specific preoccupations was nitrogen intoxication. For reasons that are still poorly understood, beneath depths of about a hundred feet nitrogen becomes a powerful intoxicant. Under its influence divers had been known to offer their air hoses to passing fish or decide to try to have a smoke break. It also produced wild mood swings. In one test, Haldane noted, the subject "alternated between depression and elation, at one moment begging to be decompressed because he felt 'bloody awful' and the next minute laughing and attempting to interfere with his colleague's dexterity test." In order to measure the rate of deterioration in the subject, a scientist had to go into the chamber with the volunteer to conduct simple mathematical tests. But after a few minutes, as Haldane later recalled, "the tester was usually as intoxicated as the testee, and often forgot to press the spindle of his stopwatch, or to take proper notes." The cause of the inebriation is even now a mystery. It is thought that it may be the same thing that causes alcohol intoxication, but as no one knows for certain what causes that we are none the wiser. At all events, without the greatest care, it is easy to get in trouble once you leave the surface world.
Which brings us back (well, nearly) to our earlier observation that Earth is not the easiest place to be an organism, even if it is the only place. Of the small portion of the planet's surface that is dry enough to stand on, a surprisingly large amount is too hot or cold or dry or steep or lofty to be of much use to us. Partly, it must be conceded, this is our fault. In terms of adaptability, humans are pretty amazingly useless. Like most animals, we don't much like really hot places, but because we sweat so freely and easily stroke, we are especially vulnerable. In the worst circumstances--on foot without water in a hot desert--most people will grow delirious and keel over, possibly never to rise again, in no more than six or seven hours. We are no less helpless in the face of cold. Like all mammals, humans are good at generating heat but--because we are so nearly hairless--not good at keeping it. Even in quite mild weather half the calories you burn go to keep your body warm. Of course, we can counter these frailties to a large extent by employing clothing and shelter, but even so the portions of Earth on which we are prepared or able to live are modest indeed: just 12 percent of the total land area, and only 4 percent of the whole surface if you include the seas.
Yet when you consider conditions elsewhere in the known universe, the wonder is not that we use so little of our planet but that we have managed to find a planet that we can use even a bit of. You have only to look at our own solar system--or, come to that, Earth at certain periods in its own history--to appreciate that most places are much harsher and much less amenable to life than our mild, blue watery globe.
So far space scientists have discovered about seventy planets outside the solar system, out of the ten billion trillion or so that are thought to be out there, so humans can hardly claim to speak with authority on the matter, but it appears that if you wish to have a planet suitable for life, you have to be just awfully lucky, and the more advanced the life, the luckier you have to be. Various observers have identified about two dozen particularly helpful breaks we have had on Earth, but this is a flying survey so we'll distill them down to the principal four. They are:
Excellent location. We are, to an almost uncanny degree, the right distance from the right sort of star, one that is big enough to radiate lots of energy, but not so big as to burn itself out swiftly. It is a curiosity of physics that the larger a star the more rapidly it burns. Had our sun been ten times as massive, it would have exhausted itself after ten million years instead of ten billion and we wouldn't be here now. We are also fortunate to orbit where we do. Too much nearer and everything on Earth would have boiled away. Much farther away and everything would have frozen.
In 1978, an astrophysicist named Michael Hart made some calculations and concluded that Earth would have been uninhabitable had it been just 1 percent farther from or 5 percent closer to the Sun. That's not much, and in fact it wasn't enough. The figures have since been refined and made a little more generous--5 percent nearer and 15 percent farther are thought to be more accurate assessments for our zon
e of habitability--but that is still a narrow belt. * 29
To appreciate just how narrow, you have only to look at Venus. Venus is only twenty-five million miles closer to the Sun than we are. The Sun's warmth reaches it just two minutes before it touches us. In size and composition, Venus is very like Earth, but the small difference in orbital distance made all the difference to how it turned out. It appears that during the early years of the solar system Venus was only slightly warmer than Earth and probably had oceans. But those few degrees of extra warmth meant that Venus could not hold on to its surface water, with disastrous consequences for its climate. As its water evaporated, the hydrogen atoms escaped into space, and the oxygen atoms combined with carbon to form a dense atmosphere of the greenhouse gas CO 2 . Venus became stifling. Although people of my age will recall a time when astronomers hoped that Venus might harbor life beneath its padded clouds, possibly even a kind of tropical verdure, we now know that it is much too fierce an environment for any kind of life that we can reasonably conceive of. Its surface temperature is a roasting 470 degrees centigrade (roughly 900 degrees Fahrenheit), which is hot enough to melt lead, and the atmospheric pressure at the surface is ninety times that of Earth, or more than any human body could withstand. We lack the technology to make suits or even spaceships that would allow us to visit. Our knowledge of Venus's surface is based on distant radar imagery and some startled squawks from an unmanned Soviet probe that was dropped hopefully into the clouds in 1972 and functioned for barely an hour before permanently shutting down.
So that's what happens when you move two light minutes closer to the Sun. Travel farther out and the problem becomes not heat but cold, as Mars frigidly attests. It, too, was once a much more congenial place, but couldn't retain a usable atmosphere and turned into a frozen waste.
But just being the right distance from the Sun cannot be the whole story, for otherwise the Moon would be forested and fair, which patently it is not. For that you need to have:
The right kind of planet. I don't imagine even many geophysicists, when asked to count their blessings, would include living on a planet with a molten interior, but it's a pretty near certainty that without all that magma swirling around beneath us we wouldn't be here now. Apart from much else, our lively interior created the outgassing that helped to build an atmosphere and provided us with the magnetic field that shields us from cosmic radiation. It also gave us plate tectonics, which continually renews and rumples the surface. If Earth were perfectly smooth, it would be covered everywhere with water to a depth of four kilometers. There might be life in that lonesome ocean, but there certainly wouldn't be baseball.
In addition to having a beneficial interior, we also have the right elements in the correct proportions. In the most literal way, we are made of the right stuff. This is so crucial to our well-being that we are going to discuss it more fully in a minute, but first we need to consider the two remaining factors, beginning with another one that is often overlooked:
We're a twin planet. Not many of us normally think of the Moon as a companion planet, but that is in effect what it is. Most moons are tiny in relation to their master planet. The Martian satellites of Phobos and Deimos, for instance, are only about ten kilometers in diameter. Our Moon, however, is more than a quarter the diameter of the Earth, which makes ours the only planet in the solar system with a sizeable moon in comparison to itself (except Pluto, which doesn't really count because Pluto is itself so small), and what a difference that makes to us.
Without the Moon's steadying influence, the Earth would wobble like a dying top, with goodness knows what consequences for climate and weather. The Moon's steady gravitational influence keeps the Earth spinning at the right speed and angle to provide the sort of stability necessary for the long and successful development of life. This won't go on forever. The Moon is slipping from our grasp at a rate of about 1.5 inches a year. In another two billion years it will have receded so far that it won't keep us steady and we will have to come up with some other solution, but in the meantime you should think of it as much more than just a pleasant feature in the night sky.
For a long time, astronomers assumed that the Moon and Earth either formed together or that the Earth captured the Moon as it drifted by. We now believe, as you will recall from an earlier chapter, that about 4.5 billion years ago a Mars-sized object slammed into Earth, blowing out enough material to create the Moon from the debris. This was obviously a very good thing for us--but especially so as it happened such a long time ago. If it had happened in 1896 or last Wednesday clearly we wouldn't be nearly so pleased about it. Which brings us to our fourth and in many ways most crucial consideration:
Timing. The universe is an amazingly fickle and eventful place, and our existence within it is a wonder. If a long and unimaginably complex sequence of events stretching back 4.6 billion years or so hadn't played out in a particular manner at particular times--if, to take just one obvious instance, the dinosaurs hadn't been wiped out by a meteor when they were--you might well be six inches long, with whiskers and a tail, and reading this in a burrow.
We don't really know for sure because we have nothing else to compare our own existence to, but it seems evident that if you wish to end up as a moderately advanced, thinking society, you need to be at the right end of a very long chain of outcomes involving reasonable periods of stability interspersed with just the right amount of stress and challenge (ice ages appear to be especially helpful in this regard) and marked by a total absence of real cataclysm. As we shall see in the pages that remain to us, we are very lucky to find ourselves in that position.
And on that note, let us now turn briefly to the elements that made us.
There are ninety-two naturally occurring elements on Earth, plus a further twenty or so that have been created in labs, but some of these we can immediately put to one side--as, in fact, chemists themselves tend to do. Not a few of our earthly chemicals are surprisingly little known. Astatine, for instance, is practically unstudied. It has a name and a place on the periodic table (next door to Marie Curie's polonium), but almost nothing else. The problem isn't scientific indifference, but rarity. There just isn't much astatine out there. The most elusive element of all, however, appears to be francium, which is so rare that it is thought that our entire planet may contain, at any given moment, fewer than twenty francium atoms. Altogether only about thirty of the naturally occurring elements are widespread on Earth, and barely half a dozen are of central importance to life.
As you might expect, oxygen is our most abundant element, accounting for just under 50 percent of the Earth's crust, but after that the relative abundances are often surprising. Who would guess, for instance, that silicon is the second most common element on Earth or that titanium is tenth? Abundance has little to do with their familiarity or utility to us. Many of the more obscure elements are actually more common than the better-known ones. There is more cerium on Earth than copper, more neodymium and lanthanum than cobalt or nitrogen. Tin barely makes it into the top fifty, eclipsed by such relative obscurities as praseodymium, samarium, gadolinium, and dysprosium.
Abundance also has little to do with ease of detection. Aluminum is the fourth most common element on Earth, accounting for nearly a tenth of everything that's underneath your feet, but its existence wasn't even suspected until it was discovered in the nineteenth century by Humphry Davy, and for a long time after that it was treated as rare and precious. Congress nearly put a shiny lining of aluminum foil atop the Washington Monument to show what a classy and prosperous nation we had become, and the French imperial family in the same period discarded the state silver dinner service and replaced it with an aluminum one. The fashion was cutting edge even if the knives weren't.
Nor does abundance necessarily relate to importance. Carbon is only the fifteenth most common element, accounting for a very modest 0.048 percent of Earth's crust, but we would be lost without it. What sets the carbon atom apart is that it is shamelessly promiscuous. It is the
party animal of the atomic world, latching on to many other atoms (including itself) and holding tight, forming molecular conga lines of hearty robustness--the very trick of nature necessary to build proteins and DNA. As Paul Davies has written: "If it wasn't for carbon, life as we know it would be impossible. Probably any sort of life would be impossible." Yet carbon is not all that plentiful even in humans, who so vitally depend on it. Of every 200 atoms in your body, 126 are hydrogen, 51 are oxygen, and just 19 are carbon. * 30
Other elements are critical not for creating life but for sustaining it. We need iron to manufacture hemoglobin, and without it we would die. Cobalt is necessary for the creation of vitamin B 12 . Potassium and a very little sodium are literally good for your nerves. Molybdenum, manganese, and vanadium help to keep your enzymes purring. Zinc--bless it--oxidizes alcohol.
We have evolved to utilize or tolerate these things--we could hardly be here otherwise--but even then we live within narrow ranges of acceptance. Selenium is vital to all of us, but take in just a little too much and it will be the last thing you ever do. The degree to which organisms require or tolerate certain elements is a relic of their evolution. Sheep and cattle now graze side by side, but actually have very different mineral requirements. Modern cattle need quite a lot of copper because they evolved in parts of Europe and Africa where copper was abundant. Sheep, on the other hand, evolved in copper-poor areas of Asia Minor. As a rule, and not surprisingly, our tolerance for elements is directly proportionate to their abundance in the Earth's crust. We have evolved to expect, and in some cases actually need, the tiny amounts of rare elements that accumulate in the flesh or fiber that we eat. But step up the doses, in some cases by only a tiny amount, and we can soon cross a threshold. Much of this is only imperfectly understood. No one knows, for example, whether a tiny amount of arsenic is necessary for our well-being or not. Some authorities say it is; some not. All that is certain is that too much of it will kill you.