Chapter Content
Okay, so, like, becoming a living thing, it's... it's not easy, you know? As far as we know, out of, like, the entire universe, only this, uh, kind of unremarkable, backwater part of the Milky Way galaxy called Earth wants you. And even then, it might not *really* want you, you know what I mean?
The whole area, like, where known life can exist, from the bottom of the deepest ocean trenches to the top of the highest mountains, is only, like, 28 kilometers thick. Which, compared to the vastness of space, is, um, basically nothing.
And for us humans, it's even worse, right? We're stuck being animals that, like, recklessly decided, four hundred million years ago, to crawl out of the sea and become land-dwelling, oxygen-breathing things. So, according to some estimates, nearly 99.5% of the world's, like, habitable space is basically... completely closed off to us.
I mean, we can't breathe underwater, obviously, but we also can't handle the pressure. Water, it's like, 1,300 times heavier than air. The deeper you go, the faster the pressure increases. Every ten meters down is like adding another atmosphere of pressure. On land, if you climb, like, 150 meters, you know, up a building or something, you barely feel the pressure change. But underwater at that same depth, your blood vessels would, like, collapse, and your lungs would be squeezed down to the size of a Coke can. It's kind of insane that people are willing to dive that deep for fun, without breathing equipment, right? Apparently, some people find it thrilling to have their internal organs, like, seriously deformed, even though the process of them going back to normal on land probably isn't so fun. To reach those depths, divers have to be dragged down, really, really fast by weights. Without help, the deepest you can go and, like, live to tell the tale is 72 meters. This Italian guy, Umberto Pelizzari, did that back, uh, a while ago. He went down to that depth, stayed for, like, a nanosecond, and then rushed back up. By land standards, 72 meters is like, you know, less than a football field. So, even when we do our craziest, most extreme stunts, we can't really say that we've mastered the ocean.
Of course, other creatures have successfully adapted to the pressure down there, but how many species actually can is a mystery. The deepest part of the ocean is the Mariana Trench in the Pacific. At about 11.3 kilometers down, the pressure's, like, over 11,000 Newtons per square centimeter. We only ever managed to send people down there in a really strong submersible once, and only for a little while. But there are creatures that *live* there, like amphipods, which are these little shrimp-like crustaceans that are transparent. They can survive down there without any protection. Most of the ocean is shallower, but even at the average depth of 4 kilometers, the pressure's the same as being crushed under, like, 14 trucks filled with cement.
Almost everyone, including ocean science writers, assumes that the huge pressure in the deep ocean would, like, crush a human body flat. But it turns out that might not actually be the case. Since we're mostly made of water ourselves, and water is, like, "virtually incompressible," according to this Oxford University professor, Francis Ashcroft, the human body would, like, stay at the same pressure as the surrounding water, so you wouldn't be crushed. The real problem is the gas inside you, especially the gas in your lungs. That *would* get compressed, but how far before it's fatal, nobody really knows. Until recently, people thought that lungs would implode and chest walls would break at, like, 100 meters, causing a horrible death. But freedivers have repeatedly shown that that's not the case. It seems like, according to Ashcroft, "people can behave more like whales and dolphins than was expected."
But there are, you know, a bunch of other things that can go wrong. Back in the day, when divers were using diving suits, those old ones that were connected to the surface with long tubes, they'd sometimes experience this, like, horrific thing called "the squeeze." This happened when the air pump on the surface failed, causing a catastrophic loss of pressure in the suit. The air would rush out, and the poor diver would literally be sucked into the mask and tubes. When they pulled him out of the water, "there would be little left inside the suit beyond bones and a bloody mush." A biologist, J.B.S. Haldane, wrote that back in the 1940s and, you know, he wanted to make sure people believed him, he added, "This has really happened."
(Oh, by the way, the original diving mask was designed by this Englishman named Charles Deane back in the early 1800s, and it wasn't even for diving. It was for firefighting. It was called a "smoke helmet for firemen." But it was made of metal, so it was, like, really hot and awkward. Deane soon realized that firefighters didn't want to wear any gear into a burning building, especially this, like, clunky, kettle-like thing. To save his investment, Deane tried it underwater and found it was perfect for maritime rescue work).
But the *real* danger in the deep ocean is decompression sickness. It's called the bends. And, uh, it's not just because it's uncomfortable, although it is, but because it's way more likely to happen. Eighty percent of the air we breathe is nitrogen. When your body's under pressure, that nitrogen turns into little bubbles and moves around in your blood and tissues. If the pressure changes too much, like if a diver comes up too fast, those bubbles foam up like a freshly opened bottle of champagne. They block the tiny blood vessels, causing cells to lose oxygen and causing the person to be doubled over in pain. Hence, "the bends."
The bends was a common problem for sponge and pearl divers for centuries, but it didn't really get noticed in the Western world until the, uh, a while ago, and even then, it affected people who didn't get wet, or at least, not above the ankles. They were caisson workers. Caissons were sealed, dry chambers built on riverbeds to build bridge supports. They were filled with compressed air. When workers came out of the caisson after working for long periods under artificial pressure, they would experience mild symptoms, like tingling or itchy skin. But, unpredictably, some would develop, like, persistent joint pain. Sometimes it'd be so bad they'd collapse, and sometimes they wouldn't get back up.
It was all very confusing. Sometimes workers would feel fine when they went to bed, but they'd wake up paralyzed. Sometimes they wouldn't wake up at all. Ashcroft tells a story about building a new tunnel under the Thames. When the tunnel was almost finished, the supervisors held a celebratory banquet. They opened champagne bottles in the compressed air of the tunnel, and they were surprised when the champagne didn't fizz. However, when they finally stepped out into the fresh London air, the bubbles instantly foamed up.
Besides avoiding high-pressure environments, there are two foolproof ways to prevent decompression sickness. One is to only experience the pressure change for a short amount of time. That's why those freedivers can dive down to 150 meters without feeling anything bad. They don't stay down there long enough for the nitrogen to dissolve into their tissues. The other way is to carefully and gradually return to the surface, so those little nitrogen bubbles dissipate without causing any harm.
We know so much about surviving in extreme environments, thanks in large part to a brilliant father-and-son team, John Scott Haldane and J.B.S. Haldane. Even by the very strict standards of British intellectuals, the Haldanes were incredibly eccentric. The elder Haldane was born into a Scottish aristocratic family, but he spent most of his life as a physiology professor at Oxford, living a pretty restrained life. He was famous for being absentminded. One time, his wife sent him upstairs to change for a dinner party, and he never came down. She found him asleep in bed in his pajamas. When he woke up, Haldane explained that he'd started undressing and assumed it was bedtime. He considered going to Cornwall to study hookworm in miners his vacation. The novelist Aldous Huxley, who lived with the Haldanes for a time, cruelly based the scientist Edward Tantamount in his novel "Antic Hay" on him.
Haldane's contribution to diving was calculating the decompression stops you need to avoid the bends when ascending from the deep. But his interests covered the whole field of physiology, from studying altitude sickness in mountain climbers to heatstroke in the desert. He was particularly interested in the effects of toxic gases on the body. To understand how carbon monoxide killed miners, he would deliberately poison himself while carefully drawing and analyzing his own blood samples. He'd only stop when he was about to lose control of his muscles and his blood saturation was 56%. Trevor Norton points out in his history of diving, that was very close to killing himself.
Haldane's son, J.B.S., was a, like, really amazing prodigy who was interested in his father's work from a young age. When he was three, he supposedly asked his father, "Is that not oxyhemoglobin or carboxyhemoglobin?" Throughout his childhood, young Haldane assisted his father with experiments. The two of them would often test gases and gas masks together, taking turns to see how long it would take them to pass out.
Young Haldane never got a science degree, he studied classics at Oxford, but he became a brilliant scientist in his own right, working for the government, mostly at Cambridge. The biologist Peter Medawar, who spent his life with incredibly smart people, called him "the cleverest man I have ever met." Huxley also based a character on young Haldane in his novel "Crome Yellow," and he used his ideas about genetic determination to develop the plot of "Brave New World." Haldane also combined Darwin's theory of evolution with Gregor Mendel's work on genetics to come up with a theory called "The New Synthesis" by geneticists.
Strangely, young Haldane found World War One to be a "thoroughly enjoyable experience," openly admitting that he "liked having a chance to kill people." He was wounded twice. After the war, he became a successful science popularizer, writing 23 books and over 400 scientific papers. His books are still readable and educational, though not always easy to find. He also became a committed Marxist, some say out of a contrarian instinct. If he'd been born in the Soviet Union, he probably would have been a monarchist. Anyway, much of his writing was originally published in the Communist "Daily Worker." While his father was interested in miners and poisoning, young Haldane focused on preventing occupational diseases in submarine crews and divers. Funded by the Admiralty, he acquired what he called a "pressure cooker," a metal cylinder that could seal three people inside at once for painful and dangerous tests. Volunteers were made to sit in ice water while breathing "abnormal gases" or undergoing rapid pressure changes. In one experiment, Haldane personally simulated the dangerous effects of a rapid ascent to see what would happen. The fillings in his teeth exploded. "Almost every experiment," Norton wrote, "ended with someone convulsing, bleeding or vomiting." The chamber was soundproof, so if someone wanted to express discomfort or pain, they had to bang on the walls or hold up signs in a small window.
Another time, Haldane inhaled increasing concentrations of oxygen, resulting in violent convulsions and broken vertebrae. Collapsed lungs and burst eardrums were common, but Haldane reassured people that "The eardrum usually heals. If a hole remains, although you will be somewhat deaf, if you smoke, smoke will come out of the corresponding ear. This is a social accomplishment."
What's unusual about this isn't that Haldane himself was willing to undergo such risks and discomfort for science, but that he could easily persuade his colleagues and relatives to climb into the chamber. His wife once convulsed for fifteen minutes during a simulated descent test. When she finally stopped thrashing on the floor, she was helped up and sent home to cook dinner. Haldane was happy to use anyone who happened to be present, including the former Spanish Prime Minister Juan Negrín. Dr. Negrín later complained of a slight tingling and "a feeling of greasiness about the lips," but was otherwise unharmed. He was lucky. During a similar oxygen-deprivation test, Haldane lost sensation in his buttocks and lower spine for six years.
One of the many problems that Haldane studied was nitrogen narcosis. For reasons that are still unclear, nitrogen becomes a highly toxic gas at depths below 30 meters. Under its influence, divers have been known to give their air hoses to passing fish or decide to take a smoking break. It also makes moods very unstable. In another experiment, Haldane noticed that one of his subjects was "alternately depressed and cheerful; at one moment feeling 'perfectly rotten' and asking to be decompressed, at the next roaring with laughter and wanting to interfere with his colleagues' sensitivity tests." To measure how quickly the subjects were deteriorating, scientists also had to climb into the pressure chamber with the volunteers to perform simple math calculations. But after a few minutes, Haldane later recalled, "the testers and the tested were usually equally narcotized, often forgetting to stop the stopwatch or make proper notes." Even now, the cause of narcosis is unclear. Some people think it's the same thing as alcohol intoxication. But since we can't even pinpoint why people get drunk, we're no better off. Anyway, if you're not careful, you can easily get into trouble the second you leave the surface world.
Which brings us back to, uh, the topic that, living on this planet isn't always easy, even though it's the only place to live. Only a small part of this planet is dry and something we can walk on. Most of *that* is too hot, too cold, too dry, too steep, or too high for us to be able to do much with it. To be fair, that's partly our own fault. We humans aren't very adaptable. Like most animals, we don't like places that are too hot. We sweat a lot, easily get heatstroke, and generally don't cope well. In the worst conditions, walking in the desert without water, most of us would become disoriented, collapse, and probably never get up again in as little as seven or eight hours. We're just as helpless against the cold. Like all mammals, humans are pretty good at generating heat, but since we barely have any hair, we're not very good at retaining it. Even in pretty warm weather, half of our calories are used to keep our bodies warm. Of course, we can use clothing and buildings to compensate for these things, but even then, the part of the Earth that we're willing or able to live in is pretty limited. It's only 12% of the total land area. If you include the oceans, it's only 4% of the total surface area of the Earth.
However, when you consider the conditions on other places in the known universe, what's amazing isn't that we use so little of our planet, but that we even found a planet where we can use any of it. You just have to look at our own solar system, or even at some periods in Earth's history, to see that most places are much more cruel and brutal to life than our warm, blue, watery planet.
It's estimated that there are a billion trillion planets in outer space. So far, space scientists have found about 70 of them outside our solar system, so humans don't really have much to say about this. But it seems like finding a planet suitable for life takes a lot of luck. Finding one suitable for advanced life takes even more. Researchers have identified, like, 20 particularly lucky chances that we've had on Earth, but this chapter's not going to go into that in detail, so they can be summarized into these four main things:
The right position. We have the right kind of star, at the right distance from the star. The star is big enough to give off a lot of heat, but not so big that it'll burn out quickly. It's all incredibly perfect. The bigger the star, the faster it burns, which is an interesting thing about physics. If our sun was ten times bigger, it would run out in ten million years instead of ten billion years, and we wouldn't be here. We're also lucky to be in our current orbit. Too close to the sun, everything on Earth would vaporize. Too far away, everything would freeze.
Back in the 1970s, an astrophysicist named Michael Hart estimated that if the Earth were even 1% further from the sun, or 5% closer, it would be uninhabitable. That's not a big margin. But it could be even bigger. Since then, those numbers have been recalculated more accurately and loosened a little, from 5% closer to 15% further. But it's still a narrow band. Since they found extremophiles in boiling mud pits in Yellowstone and similar organisms elsewhere, scientists now know that *some* life can be found in a much wider range, even under the icy surface of Pluto. We're just talking about the conditions that can produce more complex lifeforms on the surface.
To understand why the margin is so small, you just have to look at Venus. Venus is only 25 million kilometers closer to the sun than we are. The sun's heat reaches Venus only two minutes earlier than it reaches us. Venus is similar in size and structure to Earth. But that small difference in orbital distance has had a totally different result. It seems that Venus was only a little warmer than Earth when the solar system first formed, and it probably had oceans. But those few degrees warmer meant that Venus couldn't keep its surface water. The result was catastrophic for the climate. As the water evaporated, hydrogen atoms escaped into space, and oxygen and carbon formed a thick layer of the greenhouse gas carbon dioxide in the atmosphere. Venus became suffocating. There was a time, I can remember it, when astronomers hoped that there might even be life on Venus under the dense clouds, maybe even lush tropical plants, but we now know that the environment there is too extreme for any life we can imagine. Its surface temperature is 470 degrees Celsius, which is hot enough to melt lead. The atmospheric pressure on the surface of Venus is 90 times that on Earth. No one could survive it. We can't make heat-resistant suits or spacecraft, so we can't go to Venus. Our knowledge of the surface of Venus is based on radar images and some noises from a Soviet probe that landed hopefully in the clouds in the 1970s and shut down permanently in under an hour.
So, you just have to move two light-minutes closer to the sun for that to happen. If you move further away from the sun, the problem isn't that it's too hot, but that it's too cold. The freezing cold planet Mars proves that. Mars was once a more hospitable place, but it didn't keep its useful atmosphere and became a frozen, barren wasteland.
But the right distance from the sun isn't enough, otherwise the moon would be a nice place with forests. It's clearly not. You also have to have:
The right planet. I can imagine that even if you asked a geophysicist to count their blessings, not many of them would include a planet with magma inside. But it's almost certain that if there wasn't magma churning under our feet, we wouldn't be here. For one thing, our active interior spouts out a lot of gas, helping to build up our atmosphere and giving us a magnetic field to protect us from cosmic radiation. It also gives us plate tectonics, which constantly renews and folds the Earth's surface. If the Earth were completely flat, it would be covered in four kilometers of water everywhere. There might be life in those lonely oceans, but there certainly wouldn't be soccer games.
Aside from having a helpful interior, we also have the right amount of the right elements. We're made of the right stuff. This is really important for our health. We'll talk about it more fully in a bit. But let's look at the last two factors first. One of them we often forget:
We're a twin planet. Not many people think of the moon as a partner, but it really is. It’s as different as Mars’ moons are, and they're only about 10 kilometers across. Our moon's diameter is more than a quarter of the Earth's diameter. That makes our planet unique in the solar system for having a moon that's so big compared to itself. Besides Pluto, but Pluto doesn't really count because it's so small. And this is really important to us.
Without the moon's constant effect, the Earth would wobble like a top that's about to stop spinning. Who knows what the effects would be on the climate and the weather? Thanks to the moon's constant gravitational influence, the Earth can spin at the right speed and at the right angle, providing a stable environment that's needed for life to thrive and continue for a long time. This won't last forever. The moon is moving away from us at a rate of about four centimeters per year. In two billion years, it'll be too far away to keep us stable, and we'll have to find a different solution. But in the meantime, you should realize that it's much more than just a nice view in the night sky.
Astronomers have long had two ideas: that the moon and Earth were formed at the same time, or that the Earth grabbed the moon when it floated past. We talked about this in an earlier chapter. We now think that a Mars-sized object crashed into Earth about four and a half billion years ago, which threw off enough material to form the moon. This was obviously a good thing for us, especially since it happened a long time ago. If it had happened back whenever, we certainly wouldn't be happy. Which brings us to the fourth factor, which is also the most important in many ways:
The right time. The universe is unpredictable. Our existence in the universe is a miracle. If a long series of complicated events over the past four and a half billion years hadn't ended up in a certain way at a certain time, like, if the dinosaurs hadn't died out at the time because of a meteor, for one big example, you'd probably only be a few centimeters long, with antennae and a tail, sitting in a cave somewhere looking at this book.
We really don't know, because we have nothing else we can compare our own existence to. But it seems clear that if you want to end up as a pretty advanced, thoughtful society, you have to be at the right end of a long series of events, including a reasonable period of stability with the right amount of difficulties and challenges thrown in, like ice ages, and an absence of any truly big disasters.
Speaking of that, now let's talk about the elements that make us up.
There are 92 elements that are naturally found on Earth, plus about 20 made in laboratories. But we can put some of them aside. A lot of the chemical elements on Earth aren't really studied. For example, astatine hasn't really been studied. It has a name and a spot on the periodic table, right next to Marie Curie's polonium, but that's about it. It's not because science doesn't think it's important, but because it's so rare. Polonium isn't that abundant in outer space either. One of the most elusive elements is francium. Francium is so rare that at any given moment, there aren't even 20 atoms of francium on the entire planet. Out of all the elements that are found in nature, only about 30 are widely distributed on Earth, and only five or six are incredibly important to life.
You might think that oxygen is the most abundant element, making up almost 50% of the Earth's crust. But what comes after is often a surprise. Who would think that silicon is the second most common element on Earth, or that titanium is tenth? How abundant an element is has nothing to do with how familiar we are with them, or how useful they are to us. A lot of the less known elements are actually more abundant than the better known ones. There's more cerium on Earth than copper, and more neodymium and lanthanum than cobalt or nitrogen. Tin barely makes it into the top 50, falling behind the lesser-known protactinium, samarium, gadolinium, and dysprosium.
How abundant an element is also has nothing to do with how easy it is to discover. Aluminum is the fourth most common element on Earth, making up almost a tenth of everything under your feet, but it wasn't discovered until way back when. For a long time, it was considered a rare and valuable metal.
How an element looks doesn't necessarily have anything to do with how important it is. Carbon is only 15th, making up a tiny 0.048% of the Earth's crust, but we can't live without it. What makes carbon so special is that it gets along with every other element. It's like the socialite of the element world, latching onto a lot of other atoms, including itself, and holding on tight, forming happy and really strong molecular conga lines. This is where nature makes proteins and DNA, that's the secret. As Paul Davies writes, "Without carbon, life as we know it couldn't exist. It's likely that no kind of life could exist." But even though we need carbon so much, there's not that much carbon in our bodies. For every 200 atoms in your body, there are 126 hydrogen atoms, 51 oxygen atoms, and 19 carbon atoms. Of the remaining four atoms, three are nitrogen atoms, and the remaining one is shared by all the other elements.
Other elements are also important, but not for creating life, for keeping it going. We need iron to make hemoglobin. Without iron, we'd die. Cobalt is essential for making B12. Potassium and a little sodium are clearly good for the nervous system. Molybdenum, manganese, and vanadium help keep enzymes active. Zinc, may God bless it, oxidizes alcohol.
We've gradually learned to use or tolerate these things. We would barely be here otherwise. Even so, the range we can tolerate is narrow. Selenium is essential to all of us, but just a little too much and you're toast. Whether or not a living thing needs or can tolerate a certain element is the result of its evolution. Sheep and cows graze together, but they need very different minerals. Modern cows need a lot of copper because they evolved in copper-rich areas of Europe and Africa. Sheep evolved in the copper-poor area of Asia Minor. In general, how tolerant we are of an element is proportional to how abundant that element is in the Earth's crust. It's not surprising. We've evolved to the point that we hope, and in some cases, need, to have small amounts of rare elements accumulate in the meat or fiber we eat. But if we increase the dose, even just a little, we can be gone soon. We still don't know much about this. No one can really say whether ingesting a little arsenic is good or bad for our health. Some authorities say it's good. Some say it's bad. The only thing that's for sure is that too much will kill you.
Once elements combine, their properties get even stranger. Oxygen and hydrogen are two of the most flammable elements, but when combined, they become the non-flammable water. Oxygen itself isn't flammable. It just helps other things burn. Which is good. If oxygen were flammable, the air around you would suddenly burn every time you strike a match. Hydrogen is incredibly flammable. The Hindenburg disaster proved that. Back in the 1930s, the hydrogen that was lifting the Hindenburg suddenly exploded in flames, killing a lot of people. Even stranger is the compound of sodium and chlorine. Sodium is one of the least stable elements. Chlorine is one of the most poisonous. If you put a little pure sodium in water, it will explode. Poisonous chlorine is dangerous. Even small amounts of chlorine can kill. During World War I, many poison gases had chlorine in them. Many swimmers with sore eyes can prove that people don't really like chlorine, even in very small amounts. Yet, if you put these two nasty elements together, what do you get? Sodium chloride, which is ordinary table salt.
In general, we don't really accept an element if it doesn't get into our systems naturally, like, if it can't dissolve in water. Lead poisons us because we've always been exposed to it. Until we started using it for food containers and water pipes. The symbol for lead, Pb, comes from the Latin word "Plumbum," which is where we get the word "plumbing." The Romans also used lead to sweeten wine. That's maybe why they aren't as powerful as they used to be. We talked about this elsewhere. Our own use of lead isn't much to be proud of, not to mention mercury, cadmium, and other industrial pollutants, which we often use to poison ourselves. We haven't grown tolerant of any elements that aren't naturally found on Earth, so they're very toxic to us, like plutonium. Our tolerance for plutonium is zero. Even a tiny amount will kill you.
I've told you so much just to make one point. The Earth looks like it miraculously gives us a lot of things because we've gradually adapted to its conditions. What's amazing isn't that it's suitable for life, but that it's suitable for *our* lives. Maybe that's why we're happy with so many things about it, the right size sun, the caring moon, the sociable carbon, enough magma, and so on. Maybe we only *seem* to be happy because we've always depended on those conditions. No one can really say.
Living things on other worlds might be grateful for pools of silvery mercury and clouds of floating ammonia. They might be happy that their planet doesn't get dizzy with tectonic movements, doesn't spout magma all over the place, but is always in a state of non-tectonic peace. Any visitors from far away who come to Earth would laugh for sure when they found out that we live in an atmosphere made of nitrogen and oxygen. Nitrogen is too lazy to react chemically with anything. Oxygen sets everything on fire. We have to set up fire stations in every corner of the city to keep it from affecting us. Even if our visitors are oxygen-breathing bipeds who like to watch movies, they'd probably find Earth to be an awful place. We couldn't even have them over for lunch because our food has trace amounts of manganese, selenium, zinc, and other element particles. Some of those are toxic to them. Earth might not be a good place at all to them.
The physicist Richard Feynman often made fun of drawing conclusions after the fact, guessing at what might have caused something based on what we already know. "You know, something really amazing happened to me tonight," he'd say. "I saw a car with the license plate ARW357. Can you imagine that? Out of the millions of license plates in our country, how did I happen to see that one tonight? It's incredible!" He meant that it's easy to make anything mundane seem very unusual if you take it too seriously.
So, the events and conditions that led to life on Earth probably aren't as unusual as you might think. However, they're still unusual. One thing's for sure, until we find a better reason, we can only say that they're very unusual.