A Short History of Nearly Everything: Special Illustrated Edition

by Bill Bryson

  The British astrophysicist Sir Fred Hoyle, immortalized (a touch unexpectedly) in a mosaic created for Britain’s National Gallery in 1952. Hoyle thought that many earthly diseases came from outer space. (credit 19.7)

  Whatever prompted life to begin, it happened just once. That is the most extraordinary fact in biology, perhaps the most extraordinary fact we know. Everything that has ever lived, plant or animal, dates its beginnings from the same primordial twitch. At some point in an unimaginably distant past some little bag of chemicals fidgeted to life. It absorbed some nutrients, gently pulsed, had a brief existence. This much may have happened before, perhaps many times. But this ancestral packet did something additional and extraordinary: it cleaved itself and produced an heir. A tiny bundle of genetic material passed from one living entity to another, and has never stopped moving since. It was the moment of creation for us all. Biologists sometimes call it the Big Birth.

  “Wherever you go in the world, whatever animal, plant, bug or blob you look at, if it is alive, it will use the same dictionary and know the same code. All life is one,” says Matt Ridley. We are all the result of a single genetic trick handed down from generation to generation over nearly four billion years, to such an extent that you can take a fragment of human genetic instruction and patch it into a faulty yeast cell and the yeast cell will put it to work as if it were its own. In a very real sense, it is its own.

  The dawn of life—or something very like it—sits on a shelf in the office of a friendly isotope geochemist named Victoria Bennett in the Earth Sciences building of the Australian National University in Canberra. An American, Ms. Bennett came to the ANU from California on a two-year contract in 1989 and has been there ever since. When I visited her, in late 2001, she handed me a modestly hefty hunk of rock composed of thin alternating stripes of white quartz and a grey-green material called clinopyroxene. The rock came from Akilia Island in Greenland, where unusually ancient rocks were found in 1997. The rocks are 3.85 billion years old and represent the oldest marine sediments ever found.

  “We can’t be certain that what you are holding once contained living organisms because you’d have to pulverize it to find out,” Bennett told me. “But it comes from the same deposit where the oldest life was excavated, so it probably had life in it.” Nor would you find actual fossilized microbes, however carefully you searched. Any simple organisms, alas, would have been baked away by the processes that turned ocean mud to stone. Instead, what we would see if we crunched up the rock and examined it microscopically would be the chemical residues that the organisms left behind—carbon isotopes and a type of phosphate called apatite, which together provide strong evidence that the rock once contained colonies of living things. “We can only guess what the organism might have looked like,” Bennett said. “It was probably about as basic as life can get—but it was life nonetheless. It lived. It propagated.”

  And eventually it led to us.

  If you are into very old rocks, and Ms. Bennett indubitably is, the ANU has long been a prime place to be. This is largely thanks to the ingenuity of a man named Bill Compston, who is now retired but in the 1970s built the world’s first Sensitive High Resolution Ion Micro Probe—or SHRIMP, as it is more affectionately known from its initial letters. This is a machine that measures the decay rate of uranium in tiny minerals called zircons. Zircons appear in most rocks apart from basalts and are extremely durable, surviving every natural process but subduction. Most of the Earth’s crust has been slipped back into the interior at some point, but just occasionally—in Western Australia and Greenland, for example—geologists have found outcrops of rocks that have remained always at the surface. Compston’s machine allowed such rocks to be dated with unparalleled precision. The prototype SHRIMP was built and machined in the Earth Sciences Department’s own workshops, and looked like something that had been built from spare parts on a budget, but it worked great. On its first formal test, in 1982, it dated the oldest thing ever found—a 4.3-billion-year-old rock from Western Australia.

  “It caused quite a stir at the time,” Bennett told me, “to find something so important so quickly with brand-new technology.”

  She took me down the hall to see the current model, SHRIMP II. It was a big, heavy piece of stainless-steel apparatus, perhaps 3.5 metres long and 1.5 metres high, and as solidly built as a deep-sea probe. At a console in front of it, keeping an eye on ever-changing strings of figures on a screen, was a man named Bob from Canterbury University in New Zealand. He had been there since 4 a.m., he told me. It was just after 9 a.m. and Bob had the machine until noon. SHRIMP II runs twenty-four hours a day; there are that many rocks to date. Ask a pair of geochemists how something like this works, and they will start talking about isotopic abundances and ionization levels with an enthusiasm that is more endearing than fathomable. The upshot of it, however, was that the machine, by bombarding a sample of rock with streams of charged atoms, is able to detect subtle differences in the amounts of lead and uranium in the zircon samples, by which means the age of rocks can be accurately adduced. Bob told me that it takes about seventeen minutes to read one zircon and it is necessary to read dozens from each rock to make the data reliable. In practice, the process seemed to involve about the same level of scattered activity, and about as much stimulation, as a trip to a launderette. Bob seemed very happy, however; but then, people from New Zealand very generally do.

  The Earth Sciences compound was an odd combination of things—part office, part lab, part machine shed. “We used to build everything here,” she said. “We even had our own glassblower, but he’s retired. But we still have two full-time rock crushers.” She caught my look of mild surprise. “We get through a lot of rocks. And they have to be very carefully prepared. You have to make sure there is no contamination from previous samples—no dust or anything. It’s quite a meticulous process.” She showed me the rock-crushing machines, which were indeed pristine, though the rock crushers had apparently gone for coffee. Beside the machines were large boxes containing rocks of all shapes and sizes. They do indeed get through a lot of rocks at the ANU.

  Back in Bennett’s office after our tour, I noticed hanging on her wall a poster giving an artist’s colourfully imaginative interpretation of the Earth as it might have looked 3.5 billion years ago, just when life was getting going, in the ancient period known to earth science as the Archaean. The poster showed an alien landscape of huge, very active volcanoes, and a steamy, copper-coloured sea beneath a harsh red sky. Stromatolites, a kind of bacterial rock, filled the shallows in the foreground. It didn’t look like a very promising place to create and nurture life. I asked her if the painting was accurate.

  “Well, one school of thought says it was actually cool then because the sun was much weaker.” (I later learned that biologists, when they are feeling jocose, refer to this as “the Chinese restaurant problem”—because we had a dim sun.) “Without an atmosphere ultraviolet rays from the sun, even from a weak sun, would have tended to break apart any incipient bonds made by molecules. And yet right there“—she tapped the stromatolites—”you have organisms almost at the surface. It’s a puzzle.”

  Earth as it might have appeared in its Archaean infancy 3.5 billion years ago, when the Moon was much closer, volcanic eruptions commonplace (because of the thinness of the crust), meteor impacts routine and the air thick with acidic vapours. Remarkably, it was in such an unpromising environment that life first got going. (credit 19.8)

  “So we don’t know what the world was like back then?”

  “Mmmm,” she agreed thoughtfully.

  “Either way it doesn’t seem very conducive to life.”

  She nodded amiably. “But there must have been something that suited life. Otherwise we wouldn’t be here.”

  It certainly wouldn’t have suited us. If you were to step from a time machine into that ancient Archaean world, you would very swiftly scamper back inside, for there was no more oxygen to breathe on the Earth back then than there is on Mars
today. It was also full of noxious vapours from hydrochloric and sulphuric acids powerful enough to eat through clothing and blister skin. Nor would it have provided the clean and glowing vistas depicted in the poster in Victoria Bennett’s office. The chemical stew that was the atmosphere then would have allowed little sunlight to reach the Earth’s surface. What little you could see would be illumined only briefly by bright and frequent lightning flashes. In short, it was the Earth, but an Earth we wouldn’t recognize as our own.

  Anniversaries were few and far between in the Archaean world. For two billion years bacterial organisms were the only forms of life. They lived, they reproduced, they swarmed, but they didn’t show any particular inclination to move on to another, more challenging level of existence. At some point in the first billion years of life, cyano-bacteria, or blue-green algae, learned to tap into a freely available resource—the hydrogen that exists in spectacular abundance in water. They absorbed water molecules, supped on the hydrogen and released the oxygen as waste, and in so doing invented photosynthesis. As Margulis and Sagan note, photosynthesis is “undoubtedly the most important single metabolic innovation in the history of life on the planet”—and it was invented not by plants but by bacteria.

  A light micrograph showing a living colony of cyanobacteria, a type of blue-green algae whose small-scale persistence transformed the planet. (credit 19.9)

  As cyanobacteria proliferated the world began to fill with O2, to the consternation of those organisms that found it poisonous—which in those days was all of them. In an anaerobic (or non-oxygen-using) world, oxygen is extremely poisonous. Our white blood cells actually use oxygen to kill invading bacteria. That oxygen is fundamentally toxic often comes as a surprise to those of us who find it so convivial to our well-being, but that is only because we have evolved to exploit it. To other things it is a terror. It is what turns butter rancid and makes iron rust. Even we can tolerate it only up to a point. The oxygen level in our cells is only about a tenth the level found in the atmosphere.

  The new oxygen-using organisms had two advantages. Oxygen was a more efficient way to produce energy, and it vanquished competitor organisms. Some retreated into the oozy, anaerobic world of bogs and lake bottoms. Others did likewise but then later (much later) migrated to the digestive tracts of beings like you and me. Quite a number of these primeval entities are alive inside your body right now, helping to digest your food, but abhorring even the tiniest hint of O2. Untold number of others failed to adapt and died.

  The cyanobacteria were a runaway success. At first, the extra oxygen they produced didn’t accumulate in the atmosphere, but combined with iron to form ferric oxides, which sank to the bottom of primitive seas. For millions of years, the world literally rusted—a phenomenon vividly recorded in the banded iron deposits that provide so much of the world’s iron ore today. For many tens of millions of years not a great deal more than this happened. If you went back to that early Proterozoic world you wouldn’t find many signs of promise for the Earth’s future life. Perhaps here and there in sheltered pools you’d encounter a film of living scum or a coating of glossy greens and browns on shoreline rocks, but otherwise life remained invisible.

  Spirulina, another of the many types of modern cyanobacteria, consists of individual algal cells strung together to form curling strands. (credit 19.10)

  But about 3.5 billion years ago something more emphatic became apparent. Wherever the seas were shallow, visible structures began to appear. As they went through their chemical routines, the cyanobacteria became very slightly tacky, and that tackiness trapped micro-particles of dust and sand, which became bound together to form slightly weird but solid structures—the stromatolites that featured in the shallows of the poster on Victoria Bennett’s office wall. Stromatolites came in various shapes and sizes. Sometimes they looked like enormous cauliflowers, sometimes like fluffy mattresses (stromatolite comes from the Greek for mattress); sometimes they came in the form of columns, rising tens of metres above the surface of the water—on occasion as high as 100 metres. In all their manifestations, they were a kind of living rock, and they represented the world’s first co-operative venture, with some varieties of primitive organism living just at the surface and others living just underneath, each taking advantage of conditions created by the other. The world had its first ecosystem.

  For many years, scientists knew about stromatolites from fossil formations, but in 1961 they got a real surprise with the discovery of a community of living stromatolites at Shark Bay on the remote northwest coast of Australia. This was most unexpected—so unexpected, in fact, that it was some years before scientists realized quite what they had found. Today, however, Shark Bay is a tourist attraction—or at least as much of a tourist attraction as a place hundreds of miles from anywhere much and dozens of miles from anywhere at all can ever be. Boardwalks have been built out into the bay so that visitors can stroll over the water to get a good look at the stromatolites, quietly respiring just beneath the surface. They are lustreless and grey and look, as I recorded in an earlier book, like very large cow-pats. But it is a curiously giddying moment to find yourself staring at living remnants of the Earth as it was 3.5 billion years ago. As Richard Fortey has put it: “This is truly time travelling, and if the world were attuned to its real wonders this sight would be as well-known as the pyramids of Giza.” Although you’d never guess it, these dull rocks swarm with life, with an estimated (well, obviously estimated) three billion individual organisms on every square yard of rock. Sometimes when you look carefully you can see tiny strings of bubbles rising to the surface as they give up their oxygen. In two billion years such tiny exertions raised the level of oxygen in the Earth’s atmosphere to 20 per cent, preparing the way for the next, more complex chapter in life’s history.

  Fossilized cyanobacteria of a type that vanished 38 million years ago. For half of Earth’s long history, such simple organisms were the planet’s supreme biological achievement. (credit 19.11)

  It has been suggested that the cyanobacteria at Shark Bay are perhaps the most slowly evolving organisms on Earth, and certainly now they are among the rarest. Having prepared the way for more complex life forms, they were then grazed out of existence nearly everywhere by the very organisms whose existence they had made possible. (They exist at Shark Bay because the waters are too saline for the creatures that would normally feast on them.)

  One reason life took so long to grow complex was that the world had to wait until the simpler organisms had oxygenated the atmosphere sufficiently. “Animals could not summon up the energy to work,” as Fortey has put it. It took about two billion years, roughly 40 per cent of Earth’s history, for oxygen levels to reach more or less modern levels of concentration in the atmosphere. But once the stage was set, and apparently quite suddenly, an entirely new type of cell arose—one containing a nucleus and other little bodies collectively called organelles (from a Greek word meaning “little tools”). The process is thought to have started when some blundering or adventuresome bacterium either invaded or was captured by some other bacterium and it turned out that this suited them both. The captive bacterium became, it is thought, a mitochondrion. This mitochondrial invasion (or endosymbiotic event, as biologists like to term it) made complex life possible. (In plants a similar invasion produced chloroplasts, which enable plants to photosynthesize.)

  Mitochondria manipulate oxygen in a way that liberates energy from foodstuffs. Without this niftily facilitating trick, life on Earth today would be nothing more than a sludge of simple microbes. Mitochondria are very tiny—you could pack a billion into the space occupied by a grain of sand—but also very hungry. Almost every nutriment you absorb goes to feeding them.

  We couldn’t live for two minutes without them, yet even after a billion years mitochondria behave as if they think things might not work out between us. They maintain their own DNA, RNA and ribosomes. They reproduce at a different time from their host cells. They look like bacteria, divide like bacter
ia and sometimes respond to antibiotics in the way bacteria do. They don’t even speak the same genetic language as the cell in which they live. In short, they keep their bags packed. It is like having a stranger in your house, but one who has been there for a billion years.

  The new type of cells are known as eukaryotes (meaning “truly nucleated”), as contrasted with the old type, which are known as prokaryotes (“pre-nucleated”), and they seem to have arrived suddenly in the fossil record. The oldest eukaryotes yet known, called Grypania, were discovered in iron sediments in Michigan in 1992. Such fossils have been found just once and then no more are known for 500 million years.

  Earth had taken its first step towards becoming a truly interesting planet. Compared with the new eukaryotes the old prokaryotes were little more than “bags of chemicals,” to borrow from the British geologist Stephen Drury. Eukaryotes were bigger—eventually as much as ten thousand times bigger—than their simpler cousins, and could carry as much as a thousand times more DNA. Gradually, thanks to these breakthroughs, life became complex and created two types of organism—those that expel oxygen (like plants) and those that take it in (like you and me).

  Single-celled eukaryotes were once called protozoa (“pre-animals”), but that term is increasingly disdained. Today the common term for them is protists. Compared with the bacteria that had gone before, these new protists were wonders of design and sophistication. The simple amoeba, just one cell big and without any ambitions but to exist, contains 400 million bits of genetic information in its DNA—enough, as Carl Sagan noted, to fill eighty books of 500 pages.

  A fanfare of protozoa from a classic nineteenth-century work on microscopic organisms, Infusionsthierchen, by the German naturalist Christian Gottfried Ehrenberg. (credit 19.12)