Hell on Earth

01 Chapter 3 02 03 04 Hell on Earth 05 06 07 08 09 10 11 12 “Long is the way, and hard, that out of hell leads up to 13 light.” 14 John Milton, Paradise Lost 15 16 17 f you want to construct a picture of the earth on which life first 18 emerged, think about how we’ve named it. There are four geo- 19 logical eons spanning the earth’s 4,­540-​­million-​­year existence. 20 IThe most recent three names reflect our planet’s propensity for liv- 21 ing things, all referring to stages of life. The second eon is called the 22 Archean, which rather confusingly translates as “origins.” The third 23 eon is the Proterozoic, roughly translating from Greek as “earlier 24 life”; the current eon, the Phanerozoic, started around 542 million 25 years ago and means “visible life.” 26 But the first eon, the period from the formation of the earth up 27 to 3.​8 billion years ago, is called the Hadean, derived from Hades, 28 the ancient Greek version of hell. 29 Life does not merely inhabit this planet; it has shaped it and is 30 part of it. Not just in the current era of ­man-​­made climate change, S31 but all through life’s history on Earth, life has affected the rocks N32

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01 below our feet and the sky above us. And necessarily, the origin of 02 life is inseparable from the fury of the formation of the earth in the 03 first place. A picture of the Hadean earth is crucial to understanding 04 the wild natural laboratory in which life contrived to be born. Just 05 as the formation of our home world is an event in space, we’ll come 06 to see how the emergence of life here is essentially a cosmic event. 07 The study of the early geology is allrock- ­ ​­hard science, but the 08 evidence is often both literally and metaphorically thin on the 09 ground. It requires geological detective work with clues dotted 10 around the planet, and off the world, too. Geology gives us clues to 11 how the earth formed from the bits and pieces of matter floating in 12 space around the sun. Yet it also begins to describe the world that 13 will evolve into the host of the only living things that we know of. 14 While our lives are built on the stability of the earth, we also are 15 keenly aware that our planet is sporadically violently active. The 16 solid surface (including the seafloor) is made up of seven or eight 17 leviathan continental plates and a collection of smaller ones. These 18 all float on the slowly flowing but solid rock of the earth’s mantle, 19 itself encapsulating the molten core. The plates that form the crust 20 are in constant flux, grinding and unhurriedly jiggling together. 21 Some, such as the Pacific and North American plates, grind against 22 each other, forcing up new land inch by inch. The subcontinent that 23 is now India was once an island, and crunched into mainland Asia 24 in a process that began around seventy million years ago, inching 25 forward and crumpling up the land into the mountains of the Hi- 26 malayas. These mountains will continue to grow at a rate of a few 27 millimeters every year as the ­Indo-​­Australian plate continues to 28 muscle its way into mainland Asia. Others plates are pulling the 29 earth apart at the seams. The United States’ colonial expansion con- 30 tinues westward every day, as the coast of Hawaii grows new land at 31S a rate of many feet per year. with molten rock gurgling up above sea 32N level and solidifying. Earthquakes shake the land and the seabed,

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dislodging mountainous blocks of water that become tsunamis, 01 such as the one that wrecked the east coast of Japan in 2011. Still, 02 these events are currently anomalies, though they remind us that 03 our planet is alive not just with cellular life but also with slowly 04 flowing rock. Yet for the most part our earth is reassuringly stable. 05 Not so in the past. The birth of planets is a process of summon- 06 ing order from the chaos of the early solar system. Violence ensues. 07 The sun, the star at the center of our planetary system, formed 08 around 4.​6 billion years ago as a colossal cloud of ­free-​­floating mol- 09 ecules collapsed under its own gravity and condensed into the huge 10 nuclear fusion reactor that continues to heat the earth today. In the 11 immediate aftermath, the sun sat in the center of a solar nebula, a 12 flat disk of detritus left over by its formation but held there by its 13 own gravity. Over the course of the next few million years, this mat- 14 ter, mostly dust and gas, began to stick together in clumps. At first 15 these were the size of ­medium-​­size concert halls, but over hundreds 16 of centuries, lumps collided and stuck together in a process called 17 accretion. Closer to the hot sun, the temperature is higher, which 18 makes it harder for gasses to condense and accrete. It’s for this rea- 19 son that the inner four planets of the solar ­system—Mercury,​­ Venus, 20 Earth. and ­Mars—​­are terrestrial, made of rock, whereas the outer 21 four—­ Jupiter,​­ Saturn, Uranus, and Neptune—­ are​­ gaseous.1 22 It’s impossible to describe a whole planet in simple terms, as we 23 know very well how our home is not a unified land mass. Much of 24 the surface of modern Earth is solid; more is ocean. Of the grounded 25 parts, there are extremes of temperature and geography, snow, des- 26 erts, marsh, forests, plains, mountains, and so on. The rock beneath 27 your feet is likely to be very different from the rock underneath a 28 reader’s feet on the other side of the planet. Similarly, it’s virtually 29 30 S31 1 Pluto, once the ninth, is no longer considered a fully fledged planet, as it one of several ­similar-​­size bodies in that area of our solar system. N32

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01 impossible to describe simply what Earth looked like in the Hadean. 02 The evidence is vanishingly sparse, and as a result this period un- 03 helpfully gets called the Cryptic era. Yet we can extract meaningful 04 models in broad terms. We know that immediately after accretion, 05 the planet was probably largely molten. Contrary to previous think- 06 ing, however, we now think this period of molten Earth was ­short-​ 07 ­lived. There are no surviving rocks from that era, so in the past we 08 had assumed that there were no rocks. Yet the absence of evidence 09 is not the same as evidence of absence. 10 Just as we look in rocks for the traces of recent ­life—the​­ fossilized 11 forms of dinosaurs, or even cells, for ­example—​­our planet’s history 12 before life is embedded in geology. The oldest dated matter on Earth 13 comes not from rocks, but in the form of zircon crystals, an abun- 14 dant mineral found all over the world but probably best known as a 15 cheap substitute for diamonds in jewelry. 16 Zircons have two convenient characteristics. The first is that they 17 can withstand metamorphosis—­ ​­the brutal churning of rock over 18 very long periods of time. The second is that the atoms of zircons are 19 naturally arranged in a neat cubic structure. This molecular box can 20 trap atoms of uranium inside them, as few as ten parts per million. 21 A small proportion of uranium, like many elements, is radioactive, 22 and over time will decompose into lead. Due to the precise nature 23 of their crystal structure, when zircons form they can include ura- 24 nium, but exclude lead atoms. Once imprisoned in this cage, radio- 25 active uranium slowly mutates into lead over the course of millions 26 of years, and because this decomposition happens at a fixed rate 27 (what we call a ­half-​­life), the moment a zircon crystal forms, it sets 28 a clock at zero. Lead found inside zircons must have begun its life as 29 imprisoned uranium, so by quantifying it we can date the origin of 30 that crystal with 99 percent accuracy. Out in Jack Hills in Western 31S Australia, zircon crystals have been found that trapped their ura- 32N nium 4.​404 billion years ago.

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Dating is not all we can tell from the constituents of cheap jew- 01 elry. We can also infer from those same crystals that their formation 02 was part of a solidifying process, the development of a crust. This 03 means that, although there are no rocks from that period, we can 04 know that there was land in the Hadean. We can also determine 05 what other ingredients were present. The Jack Hills zircons also har- 06 bor a particular type of radioactive oxygen whose presence looks 07 like that found in modern crystals, which are formed as the earth’s 08 crust gets sucked down beneath the ocean floor. The presence of this 09 oxygen suggests that from as little as a hundred million years after 10 the initial molding of the earth, water was present. On Earth, there 11 is no life without it, though this water was likely to have been ex- 12 tremely acidic.2 13 Therefore, the early Cryptic days on Earth might not have been 14 quite the hellish inferno of endless seas of molten lava. Within a 15 mere hundred million years, the earth had a solid surface and 16 oceans. Sounds pleasant enough, but let’s not paint such a pictur- 17 esque portrait. The earlier theories of a molten Hadean Earth were 18 based on a solid observation: we can’t find any rocks from that era. 19 If there was a rocky surface, what in hell’s name happened to it? 20 It turned out that we were looking in the wrong place. In fact, we 21 were looking on the wrong heavenly body altogether. To address the 22 question of what happened to the early earth, we sent twelve men to 23 the moon. The moon itself was born out of the most destructive 24 impact that Earth has yet suffered. Somewhere between fifty and 25 one hundred million years after the formation of our solar system, 26 the earth had its worst day. It was struck by Theia—­ a​­ terrifically and 27 28 2 The source of the earth’s water remains controversial. The absence of an atmo- 29 sphere and its position in space so close to the sun may have caused much water on Earth to evaporate. Yet perhaps the shape of the rocks that first accreted to form 30 this planet held water in their crannies. Another idea that some scientists promote S31 is that most of the water on Earth was delivered in one or several icy comets whose frozen payload melted on delivery. N32

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01 inappropriately pretty name for such a harbinger of doom. Current 02 theories suggest that Theia was a rock the size of Mars. It blasted 03 enough matter from the embryonic earth into space that it reformed 04 as our closest celestial neighbor: the Moon. The impact was devas- 05 tating, enough to rip the first atmosphere from the planet. Theia’s 06 glancing blow may be what shifted the earth’s axis from vertical to 07 its ­off-​­kilter stance of 23.​5°. This lean is what causes the seasons, as 08 the distance from the sun varies with the axial tilt of the earth. 09 But it was what came after the formation of the moon that con- 10 cerns us. It’s the characteristic ­pock-​­marked lunar visage that gave 11 us clues to the state of the Hadean earth. Between 1969 and 1972 the 12 Apollo program of the U.S.​ National Aeronautics and Space Admin- 13 istration (NASA) landed six missions and twelve explorers on the 14 moon, beginning with Neil Armstrong’s famous first small step. 15 Over those missions, astronauts collected around half a ton of rock 16 and brought it back home for analysis. The last man to walk on the 17 moon, Commander Gene Cernan in Apollo 17, is quoted as saying 18 that “we went to explore the Moon, and in fact discovered the 19 Earth.” There is a great truth in that quotation, as it was in the sub- 20 sequent analysis of lunar rocks that we were to discover the nature 21 of the earth’s formative years. Unlike the earth, the moon has no 22 atmosphere or winds, and no shifting geology, so the craters formed 23 by meteorite impacts are left undisturbed alongside the footprints 24 of the Apollo pioneers. What that means is that we have a record of 25 meteorite activity in the local solar system, footprints unscathed by 26 the winds, seas and tectonic grind of the earth. Geologists dated 27 lunar rocks bearing the hallmarks of meteor strikes. These are called 28 impact melt rocks; they all occurred in a precise window of time, 29 between 4.​1 and 3.​8 billion years ago. We can deduce that this was 30 a period of intense local meteoric activity, and by inference, that the 31S earth also suffered this hellish pummeling from above. The young 32N

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solar system was crowded with debris and leftovers from its birth, 01 and for a period of three hundred million years, until the end of the 02 Hadean, we got the full brunt of it. This period is called the Late 03 Heavy ­Bombardment—​­so named because it was mercifully the last 04 time Earth would suffer such a battering. 05 How heavy is heavy? Meteors fall from the skies all the time. 06 Almost all, thank goodness, are tiny, burn out, then fade away in the 07 atmosphere as shooting stars. Occasionally, a big one hits, where- 08 upon they become meteorites, such as one that fell on the small 09 Australian town of Murchison in September 1969, just a few weeks 10 after Apollo 11 returned Armstrong, Buzz Aldrin, and command 11 module pilot Michael Collins to Earth. That one weighed more than 12 two hundred pounds, and carried a payload of interest to this story, 13 as we will find out later. 14 If you’re prone to making a wish when you see a shooting star, 15 why not hope that we don’t get to witness anything near the size of 16 the ­best-​­known meteorite. ­Sixty-​­five million years ago a ­five-​­ or ­six-​ 17 ­mile-wide​­ rock smashed into an area of what we now call Chicxulub 18 in Mexico. The crater is now hidden, mostly beneath the sea, but its 19 ­110-​­mile-​­wide shadow remains and was spotted by oil prospectors 20 in the 1970s. In the ground and seabed, there is a broken but detect- 21 able ectopic circle of tiny glass beads that were forged from molten 22 rock during the heat of impact. And from space we can see the same 23 circle in minuscule gravity distortions only measurable from preci- 24 sion equipment in satellite orbit. There has not been an impact any- 25 where near that magnitude since then, and be thankful for that. The 26 Chicxulub meteorite was the trigger that extinguished the reign of 27 the dinosaurs and paved the way for small mammals to evolve, 28 eventually into us. An impact of that order means that it’s very likely 29 that the meteorite instantaneously wiped out many millions of crea- 30 tures, with an expanding circumference of ­mile-high​­ megatsunamis S31 N32

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01 racing away from the impact site, leveling the land like a wave crash- 02 ing on a beach. With that there also would have been a fireball hot 03 enough to melt sand and rock into those telltale glass beads. But the 04 full impact of the meteorite would have taken thousands of years, a 05 dust cloud thrown up that blotted out the sun. The Chicxulub im- 06 pact irreversibly changed the earth’s system, wiping out once dom- 07 inant ­life-​­forms. And yet compared to what was happening on the 08 infant planet, the place on which life began, Chicxulub was a drop 09 in the ocean. 10 Scientists have estimated that during the Late Heavy Bombard- 11 ment something like fifteen astronomical rocks over one hundred 12 miles wide, twenty times the size of Chicxulub, bruised our world. 13 Of these maybe four of them were two hundred miles wide. For 14 three hundred million years, giant rocks rained down from the sky, 15 some as big as ­decent-​­size islands. The power of any one of the tens 16 of thousands of impacts during this time would make the most de- 17 structive nuclear bomb seem like firecracker. Global environmental 18 destruction would have occurred at least every few centuries. Any 19 potential surface habitat for living organisms would have been de- 20 stroyed over and over and over again. The relentless pounding the 21 planet suffered during the Late Heavy Bombardment was enough to 22 boil the oceans and vaporize the land. 23 And then it significantly calmed down. The meteoric blitz of the 24 Hadean ended around 3.8​ billion years ago, leaving a frazzled earth, 25 still tempestuous and rough, but at least not barraged from the 26 skies. The sun was dimmer than today, probably less thanthree- ­ ​ 27 ­quarters of its current strength. Because of that, the earth cooled 28 quickly, and water from volcanoes and comets condensed into 29 oceans that covered the planet. 30 The precise point at which life began is unknown, and almost 31S certainly unknowable. It may be that it began multiple times, maybe 32N

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during the Hadean, but was wiped out all but once by the sterilizing 01 spray of Late Heavy Bombardment. One 2009 computer model by 02 scientists in Colorado suggests that even had the Hadean eon steril- 03 ized the surface of the Earth, life could have survived at the bottom 04 of the ocean. 05 The consensus (though not unchallenged) is that the first evi- 06 dence for living matter dates to around 3.​8 billion years ago, coin- 07 ciding with the end of the Late Heavy Bombardment. These clues 08 come in the form of that vitally important atom, carbon. Cells, de- 09 fining life as we know it, are not visible in the fossil record at this 10 age, as rocks older than 3.​5 billion years tend to have undergone the 11 harsh geological metamorphosis that irretrievably churns up any 12 shadow of living structures. Therefore, we have to look for the 13 chemical signatures of life trapped in rocks. In a formation on the 14 west coast of Greenland, rocks have been found that contain the 15 merest trace of a form of radioactive carbon that has no earthly 16 reason to be there, unless it had been processed by a living organism. 17 We don’t know what that life-­ ​­form was: only by the presence of 18 that carbon can we infer that an organism that had similar funda- 19 mental mechanisms to modern life existed all that time ago. Skip 20 forward four hundred million years and the remnants of life are 21 abundant and much less controversial.3 The best of these comes in 22 the form of stromatolites: foot-­ ​­wide stone mushrooms that sprout 23 from the shallow seas in Australia and other locations around the 24 world. They are formed when floating mats of ­solar-​­powered bacte- 25 ria trap tiny particles of grit in their slimy mucus, and over millen- 26 nia this floating scum slowly settles into layered lumps of stone. 27 28

3 I say “less controversial,” as some scientists contest that stromatolites could 29 form from a nonbiological ­process—abiogenesis.​­ Nevertheless, the consensus leans 30 heavily toward these rocks being strong evidence for an Archean world thronging with microbial life. S31 N32

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01 02 03 Ingredients 04 05 Yet that is hundreds of millions of years of evolution after the end of 06 the Late Heavy Bombardment. What we see from then are scant 07 pieces bearing evidence of living things in a colossal jigsaw. We have 08 a picture of Earth, more settled than it had been for hundreds of mil- 09 lions of years, but still violent, with electrical storms, churning land 10 masses, volcanoes chugging out gasses into the atmosphere, and tu- 11 multuous seas. This is a contemporary understanding of the early 12 earth, and has helped us formulate experiments and hypotheses for 13 the conditions in which life emerged. However, the first speculations 14 about life’s emergence predate our current ones by a century. 15 In 1871, Darwin wrote a letter to his friend Joseph Hooker con- 16 templating the switch from inanimate chemistry to life. On the sec- 17 ond page of this almost unreadable document4 he considers not the 18 origin of species, but the origin of life: 19 20 It is often said that all the conditions for the first pro- 21 duction of a living organism are now present, which 22 could ever have been present. But if (and oh what a big if) 23 we could conceive in some warm little pond with all sorts 24 of ammonia and phosphoric salts,—light, heat, electricity 25 &​c. present, that a protein compound was chemically 26 formed, ready to undergo still more complex changes, at 27 the present day such matter wd be instantly devoured, or 28 absorbed, which would not have been the case before liv- 29 ing creatures were formed. 30 31S 4 Darwin’s handwriting was extraordinarily sloppy, to say the least, and the 32N original letter is barely legible.

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With this famous “warm little pond” Darwin is prefiguring the 01 concept of primordial soup (primeval, meaning “original” or the 02 “earliest time,” and prebiotic, meaning “before life,” are also used, 03 largely interchangeably). He lists the ingredients of the soup there, 04 just like a recipe. Though ignorant of our modern picture of the 05 Archaean earth, Darwin had casually meandered into what would 06 become the dominant idea of the origin of life. He was not the only 07 one to take these speculative baby steps. One of his biggest champi- 08 ons was the German zoologist and polymath Ernst Haeckel, an early 09 proponent of the idea that biology and chemistry were continua- 10 tions on the same spectrum. In 1892, he proposed a process in 11 which “the origin of a most simple organic individual in an inor- 12 ganic formative fluid, that is, in a fluid which contains the funda- 13 mental substances for the composition of the organism dissolved in 14 simple and loose combinations.” Chemists were already dabbling in 15 biological alchemy, not gold from base, but conjuring the molecules 16 of biology from chemistry. In 1828, a German scientist, Friedrich 17 Wöhler, synthesized urea, a key biological molecule and a compo- 18 nent of urine, noting in his methods that he had done it “without the 19 use of kidneys, either man or dog.” This contradicted the ­then-​ 20 ­popular concept of vitalism, that life was somehow fundamentally 21 different from nonlife. Wöhler had shown that the molecules of life 22 could be made synthetically. 23 The idea that the birthplace of the first life was a rich pond of 24 ingredients was formalized in the 1920s when a Russian, Aleksander 25 Oparin, and an Englishman, J. B. S. Haldane, both independently 26 wrote about the emergence of complex biological molecules and life 27 in conditions fueled by an ­oxygen-depleted​­ atmosphere on the early 28 earth. Haldane—­ ​­a truly great scientist who went on to become a 29 central figure in the emergence of evolutionary biology in the twen- 30 tieth century and a gifted sciencecommunicator— ­ ​­is an important S31 character in this scientific journey, as he first used the phrase N32

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01 “prebiotic soup,” and the idea of soup as the stock of life has bubbled 02 away ever since. 03 Soup had its greatest moment in 1953, a vintage year for science. 04 Crick and Watson revealed the structure of DNA in April, certainly 05 the scientific achievement of the twentieth century. But at exactly 06 the same time, a young student was building on Haldane’s and Opa- 07 rin’s ideas to put together another, similarly iconic experiment. 08 Stanley Miller was a ­twenty-​­two-​­year-​­old chemist at the University 09 of Chicago, and as part of his PhD he begged his supervisor, Nobel 10 Prize laureate Harold Urey, to let him put together a rather fanciful 11 experiment. He built a set of interconnected glass pipes on an elec- 12 trified metal grid six and a half feet square. This kit now sits in a 13 dimly lit room in the labs of one of Miller’s students, Jeffrey Bada, 14 now an emeritus professor at the Scripps Institution of Oceanogra- 15 phy in San Diego. It looks, not inappropriately, like a 1950s sci‑fi 16 experiment, with sparks and bubbling gasses and colored liquids. 17 Miller filled the glass beakers with water, methane, hydrogen, and 18 ammonia, in an attempt to emulate what was believed at the time to 19 be the essential ingredients of the early earth. Moving on to the next 20 stage set by Oparin and Haldane, Miller reasoned that the absence 21 of oxygen in the atmosphere was key to the chemical maelstrom 22 necessary to prompt the emergence of essential biological mole- 23 cules. Miller put thousands of volts’ worth of spark into that pipe- 24 work, mocking the electrical storms and lightning that thundered 25 from the turbulent Archaean sky. 26 Harold Urey had the good grace to let him pursue this experi- 27 ment with the caveat that it would be shut down and he would have 28 to move on to less implausible research if it bore no fruit within a 29 few months. No such time was needed. Within days the mix turned 30 pink, then coffee brown. Miller extracted the rich brew; his analysis 31S of it found the presence of the amino acid glycine and a handful of 32N the other biological amino acids essential for building proteins. He

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published his results in the journal Science, noting in the methods 01 that the conditions were designed to emulate the primitive earth, 02 not to optimize the production of amino acids. Just to consolidate 03 that extraordinary result, there’s a sweet coda to this experiment. In 04 2008, a year after Miller died, Jeffrey Bada rediscovered some of the 05 original samples from this experiment tucked away in the back of a 06 dusty draw. He then subjected them to ­twenty-​­first-​­century analy- 07 ses. Even in these ­fifty-​­year-​­old samples, precision inspection re- 08 vealed not just the few that Miller had seen, but all twenty of the 09 biological amino acids, and five others, too. It seems that under 10 those conditions, the spontaneous production of essential biological 11 ingredients was a trivially straightforward happenstance. Those 12 simple units, it might be thought, would string together into pro- 13 teins that all life depends on, and with their function the processes 14 of life could begin. Miller had shown that in the tumult of the Ar- 15 chaean earth, the molecules that form the universal workers of liv- 16 ing ­systems—​­proteins—​­were simply summoned into existence by 17 the equivalent of a bolt of lightning. 18 The experiment was so appealing that Miller became an interna- 19 tional celebrity. The press was amazed and excited;, their reporting 20 exaggerated the results to the point where some claimed that Miller 21 had created life. Naturally, amino acids are not life, though they are 22 essential for it, and their creation was big news. This experiment was 23 seen as a stamp of approval for the idea of primordial soup, cement- 24 ing its place as part of our culture, and the most tenacious idea in 25 the origin of life. In a location somewhere on the earth, a wet surface 26 or pool or floating pumice was exposed to the gasses of the Ar- 27 chaean atmosphere and a bolt of lightning. It carries a sense of 28 drama: the spark of life injected into a corpse, invigorated from the 29 skies – the moment of creation. 30 But could it have been like this? As we have seen in earlier chap- S31 ters, the mechanics of life are mesmerizingly complicated. A cell is N32

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01 a hive of densely packed activity receiving input from its environ- 02 ment (whether this environment is as part of an organism or as a 03 single free-­ ​­living cell). Inside the cell, there is code that encrypts 04 proteins, and those proteins enact the functions of living: feeding, 05 communications with other cells, and the reproduction of the or- 06 ganism to perpetuate the genes it bears. To see the spontaneous 07 emergence in a test tube of the molecules (or components of those 08 molecules) that perform these vital acts certainly provides credence 09 to the idea that the origin of life is neither mystical nor supernatu- 10 ral. At the beginning of the Archaean, simple chemical ingredients 11 did make the transition from chemistry to biology, and Miller’s 12 iconic experiment follows in the direct scientific lineage of Darwin’s 13 warm little pond. In that charming speculation the recipe includes 14 “ammonia and phosphoric salts,—light, heat, electricity &​c.,” all of 15 which are plausible components as they relate to some of a typical 16 cell’s processes. Miller’s experiment tested this idea, basing the in- 17 gredients on a better understanding of the conditions of the infant 18 ­earth—​­ammonia, methane, hydrogen, water, and lightning. In the 19 sixty years since, many experiments have further refined the recipe, 20 or shown similar and more sophisticated spontaneous construction 21 of biological molecules out of a soup of ingredients. It’s an attractive 22 idea, and one that has stuck. But there are fundamental outstanding 23 questions that underlie these experiments. Can life emerge by cook- 24 ing up a chemical soup? Is a spark what it takes to drive a chemical 25 reaction into a biological one? To answer these questions, and to get 26 to the bottom of the origin of life, we must ask a very simple ques- 27 tion, one with a deeply elusive answer. 28 29 30 31S 32N

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