by Bill Bryson
Much the same can be said of many other seafoods. In the New England fisheries off Rhode Island, it was once routine to haul in lobsters weighing 9 kilograms. Sometimes they reached over 13 kilos. Left unmolested, lobsters can live for decades—as much as 70 years, it is thought—and they never stop growing. Nowadays few lobsters weigh more than 1 kilogram on capture. “Biologists,” according to the New York Times, “estimate that 90 per cent of lobsters are caught within a year after they reach the legal minimum size at about age six.” Despite declining catches, New England fishermen continue to receive state and federal tax incentives that encourage them—in some cases all but compel them—to acquire bigger boats and to harvest the seas more intensively. Today the fishermen of Massachusetts are reduced to fishing the hideous hagfish, for which there is a slight market in the Far East, but even their numbers are now falling.
By 1960, the number of spawning cod in the north Atlantic had fallen to an estimated 1.6 million tonnes. By 1990 this had sunk to 22,000 tonnes.
Cod, once so abundant that they could be scooped up in baskets lowered over the sides of ships, are now commercially extinct across much of the north Atlantic. (credit 18.15)
We are remarkably ignorant of the dynamics that rule life in the sea. While marine life is poorer than it ought to be in areas that have been overfished, in some naturally impoverished waters there is far more life than there ought to be. The southern oceans around Antarctica produce only about 3 per cent of the world’s phytoplankton—far too little, it would seem, to support a complex ecosystem, and yet they do. Crab-eater seals are not a species of animal that most of us have heard of, but they may actually be the second most numerous large species of animal on Earth, after humans. As many as 15 million of them may live on the pack ice around Antarctica. There are also perhaps 2 million Weddel seals, at least half a million Emperor penguins, and maybe as many as 4 million Adelie penguins. The food chain is thus hopelessly top-heavy, but somehow it works. Remarkably, no-one knows how.
All this is a very roundabout way of making the point that we know very little about Earth’s biggest system. But then, as we shall see in the pages remaining to us, once you start talking about life, there is a great deal we don’t know—not least, how it got going in the first place.
A flock of penguins cling to a precarious perch on the frigid edge of Antarctica, proof that life exists wherever it can. Surprisingly, the pack ice around Antarctica is home to some of the largest populations of animals on Earth. (credit c.16)
1 The indigestible parts of giant squid, in particular their beaks, accumulate in sperm whales’ stomachs into the substance known as ambergris, which is used as a fixative in perfumes. The next time you spray on Chanel Number 5 (assuming you do), you may wish to reflect that you are dousing yourself in distillate of unseen sea monster.
Perhaps the slowest evolving of all life forms, and now among the rarest, are stromatolites—a kind of living rock made by billions and billions of microscopic cyanobacteria. The tiny respirations of these organisms over millions of years largely created Earth’s oxygen-rich atmosphere, paving the way for more complex living things. These specimens are from Shark Bay in Australia. (credit 19.1)
THE RISE OF LIFE
In 1953 Stanley Miller, a graduate student at the University of Chicago, took two flasks—one containing a little water to represent a primeval ocean, the other holding a mixture of methane, ammonia and hydrogen sulphide gases to represent the Earth’s early atmosphere—connected them with rubber tubes and introduced some electrical sparks as a stand-in for lightning. After a few days, the water in the flasks had turned green and yellow in a hearty broth of amino acids, fatty acids, sugars and other organic compounds. “If God didn’t do it this way,” observed Miller’s delighted supervisor, the Nobel laureate Harold Urey, “He missed a good bet.”
Press reports of the time made it sound as if about all that was needed now was for somebody to give the flasks a good shake and life would crawl out. As time has shown, it wasn’t nearly so simple. Despite half a century of further study, we are no nearer to synthesizing life today than we were in 1953—and much further away from thinking we can. Scientists are now pretty certain that the early atmosphere was nothing like as primed for development as Miller and Urey’s gaseous stew, but rather was a much less reactive blend of nitrogen and carbon dioxide. Repeating Miller’s experiments with these more challenging inputs has so far produced only one fairly primitive amino acid. At all events, creating amino acids is not really the problem. The problem is proteins.
Proteins are what you get when you string amino acids together, and we need a lot of them. No-one really knows, but there may be as many as a million types of protein in the human body, and each one is a little miracle. By all the laws of probability proteins shouldn’t exist. To make a protein you need to assemble amino acids (which I am obliged by long tradition to refer to here as “the building blocks of life”) in a particular order, in much the same way that you assemble letters in a particular order to spell a word. The problem is that words in the amino-acid alphabet are often exceedingly long. To spell “collagen,” the name of a common type of protein, you need to arrange eight letters in the right order. To make collagen, you need to arrange 1,055 amino acids in precisely the right sequence. But—and here’s an obvious but crucial point—you don’t make it. It makes itself, spontaneously, without direction, and this is where the unlikelihoods come in.
The chances of a 1,055-sequence molecule like collagen spontaneously self-assembling are, frankly, nil. It just isn’t going to happen. To grasp what a long shot its existence is, visualize a standard Las Vegas slot machine but broadened greatly—to about 27 metres, to be precise—to accommodate 1,055 spinning wheels instead of the usual three or four, and with twenty symbols on each wheel (one for each common amino acid)1 How long would you have to pull the handle before all 1,055 symbols came up in the right order? Effectively, for ever. Even if you reduced the number of spinning wheels to 200, which is actually a more typical number of amino acids for a protein, the odds against all 200 coming up in a prescribed sequence are 1 in 10260 (that is a 1 followed by 260 zeros). That in itself is a larger number than all the atoms in the universe.
Proteins, in short, are complex entities. Haemoglobin is only 146 amino acids long, a runt by protein standards, yet even it offers 10190 possible amino-acid combinations, which is why it took the Cambridge University chemist Max Perutz twenty-three years—a career, more or less—to unravel it. For random events to produce even a single protein would seem a stunning improbability—like a whirlwind spinning through a junkyard and leaving behind a fully assembled jumbo jet, in the colourful simile of the astronomer Fred Hoyle.
Stanley Miller of the University of Chicago in 1953, soon after announcing an experiment that seemed to offer the possibility of life in a test tube. The hope proved decidedly premature. (credit 19.2)
Yet we are talking about several hundred thousand types of protein, perhaps a million, each unique and each, as far as we know, vital to the maintenance of a sound and happy you. And it goes on from there. To be of use, a protein must not only assemble amino acids in the right sequence, it must then engage in a kind of chemical origami and fold itself into a very specific shape. Even having achieved this structural complexity, a protein is no good to you if it can’t reproduce itself, and proteins can’t. For this you need DNA. DNA is a whiz at replicating—it can make a copy of itself in seconds—but can do virtually nothing else. So we have a paradoxical situation. Proteins can’t exist without DNA and DNA has no purpose without proteins. Are we to assume, then, that they arose simultaneously with the purpose of supporting each other? If so: wow.
And there is more still. DNA, proteins and the other components of life couldn’t prosper without some sort of membrane to contain them. No atom or molecule has ever achieved life independently. Pluck any atom from your body and it is no more alive than is a grain of sand. It is only when they come together within th
e nurturing refuge of a cell that these diverse materials can take part in the amazing dance that we call life. Without the cell, they are nothing more than interesting chemicals. But without the chemicals, the cell has no purpose. As Davies puts it, “If everything needs everything else, how did the community of molecules ever arise in the first place?” It is rather as if all the ingredients in your kitchen somehow got together and baked themselves into a cake—but a cake that could moreover divide when necessary to produce more cakes. It is little wonder that we call it the miracle of life. It is also little wonder that we have barely begun to understand it.
So what accounts for all this wondrous complexity? Well, one possibility is that perhaps it isn’t quite—not quite—so wondrous as at first it seems. Take those amazingly improbable proteins. The wonder we see in their assembly comes in assuming that they arrived on the scene fully formed. But what if the protein chains didn’t assemble all at once? What if, in the great slot machine of creation, some of the wheels could be held, as a gambler might hold a number of promising cherries? What if, in other words, proteins didn’t suddenly burst into being, but evolved?
Computer model showing the tortuous—but crucially specific—ribbons and curls that make up a protein’s shape. To perform its function, a protein (this one is myoglobin, which is found in muscle tissue) must have exactly the right components correctly folded into exactly the right shape. (credit 19.3)
Imagine if you took all the components that make up a human being—carbon, hydrogen, oxygen and so on—and put them in a container with some water, gave it a vigorous stir and out stepped a completed person. That would be amazing. Well, that’s essentially what Hoyle and others (including many ardent creationists) argue when they suggest that proteins spontaneously formed all at once. They didn’t—they can’t have. As Richard Dawkins argues in The Blind Watchmaker, there must have been some kind of cumulative selection process that allowed amino acids to assemble in chunks. Perhaps two or three amino acids linked up for some simple purpose and then after a time bumped into some other similar small cluster and in so doing “discovered” some additional improvement.
Chemical reactions of the sort associated with life are actually something of a commonplace. It may be beyond us to cook them up in a lab, à la Stanley Miller and Harold Urey, but the universe does it readily enough. Lots of molecules in nature get together to form long chains called polymers. Sugars constantly assemble to form starches. Crystals can do a number of lifelike things—replicate, respond to environmental stimuli, take on a patterned complexity. They’ve never achieved life itself, of course, but they demonstrate repeatedly that complexity is a natural, spontaneous, entirely reliable event. There may or may not be a great deal of life in the universe at large, but there is no shortage of ordered self-assembly, in everything from the transfixing symmetry of snowflakes to the comely rings of Saturn.
Snowflakes, like all crystals, are marvels of spontaneous design and a reminder that ordered complexity is commonplace in the universe. (credit 19.4)
So powerful is this natural impulse to assemble that many scientists now believe that life may be more inevitable than we think—that it is, in the words of the Belgian biochemist and Nobel laureate Christian de Duve, “an obligatory manifestation of matter, bound to arise wherever conditions are appropriate.” De Duve thought it likely that such conditions would be encountered perhaps a million times in every galaxy.
Certainly there is nothing terribly exotic in the chemicals that animate us. If you wished to create another living object, whether a goldfish or a head of lettuce or a human being, you would need really only four principal elements, carbon, hydrogen, oxygen and nitrogen, plus small amounts of a few others, principally sulphur, phosphorus, calcium and iron. Put these together in three dozen or so combinations to form some sugars, acids and other basic compounds and you can build anything that lives. As Dawkins notes: “There is nothing special about the substances from which living things are made. Living things are collections of molecules, like everything else.”
The bottom line is that life is amazing and gratifying, perhaps even miraculous, but hardly impossible—as we repeatedly attest with our own modest existences. To be sure, many of the fine details of life’s beginnings remain pretty imponderable. Every scenario you have ever read concerning the conditions necessary for life involves water—from the “warm little pond” where Darwin supposed life began to the bubbling sea vents that are now the most popular candidates for life’s beginnings—but all this overlooks the fact that to turn monomers into polymers (which is to say, to begin to create proteins) involves a type of reaction known to biology as “dehydration linkages.” As one leading biology text puts it, with perhaps just a tiny hint of discomfort, “Researchers agree that such reactions would not have been energetically favorable in the primitive sea, or indeed in any aqueous medium, because of the mass action law.” It is a little like putting sugar in a glass of water and having it become a cube. It shouldn’t happen, but somehow in nature it does. The actual chemistry of all this is a little arcane for our purposes here, but it is enough to know that if you make monomers wet they don’t turn into polymers—except when creating life on the Earth. How and why it happens then and not otherwise is one of biology’s great unanswered questions.
One of the biggest surprises in the earth sciences in recent decades was discovering just how early in Earth’s history life arose. Well into the 1950s, it was thought that life was less than six hundred million years old. By the 1970s, a few adventurous souls felt that maybe it went back 2.5 billion years. But the present date of 3.85 billion years is stunningly early. The Earth’s surface didn’t become solid until about 3.9 billion years ago.
A meteor streaks across the sky of Wales in 2003. Most meteors burn up harmlessly in the atmosphere. Those that strike the ground become known as meteorites. (credit 19.5)
“We can only infer from this rapidity that it is not ‘difficult’ for life of bacterial grade to evolve on planets with appropriate conditions,” Stephen Jay Gould observed in the New York Times in 1996. Or as he put it elsewhere, it is hard to avoid the conclusion that “life, arising as soon as it could, was chemically destined to be.”
Life emerged so swiftly, in fact, that some authorities think it must have had help—perhaps a good deal of help. The idea that earthly life might have arrived from space has a surprisingly long and even occasionally distinguished history. The great Lord Kelvin himself raised the possibility as long ago as 1871 at a meeting of the British Association for the Advancement of Science, when he suggested that “the germs of life might have been brought to the earth by some meteorite.” But it remained little more than a fringe notion until one Sunday in September 1969 when tens of thousands of Australians were startled by a series of sonic booms and the sight of a fireball streaking from east to west across the sky. The fireball made a strange crackling sound as it passed and left behind a smell that some likened to methylated spirits and others described as just awful.
A prized chunk from the celebrated fireball that exploded over Murchison, Australia, in 1969. (credit 19.6)
The fireball exploded above Murchison, a town of six hundred people in the Goulburn Valley north of Melbourne, and came raining down in chunks, some weighing over 5 kilograms. Fortunately, no-one was hurt. The meteorite was of a rare type known as a carbonaceous chondrite, and the townspeople helpfully collected and brought in some 90 kilograms of it. The timing could hardly have been better. Less than two months earlier, the Apollo 11 astronauts had returned to Earth with a bag full of lunar rocks, so labs throughout the world were geared up—indeed, clamouring—for rocks of extraterrestrial origin.
The Murchison meteorite was found to be 4.5 billion years old, and it was studded with amino acids—seventy-four types in all, eight of which are involved in the formation of earthly proteins. In late 2001, more than thirty years after it crashed, a team at the Ames Research Center in California announced that the Murchison rock also
contained complex strings of sugars called polyols, which had not been found off the Earth before.
A few other carbonaceous chondrites have strayed into the Earth’s path since 1969—one that landed near Tagish Lake in Canada’s Yukon in January 2000 was seen over large parts of North America—and they have likewise confirmed that the universe is actually rich in organic compounds. Halley’s comet, it is now thought, is about 25 per cent organic molecules. Get enough of those crashing into a suitable place—Earth, for instance—and you have the basic elements you need for life.
There are two problems with notions of panspermia, as extraterrestrial theories are known. The first is that it doesn’t answer any questions about how life arose, but merely moves responsibility for it elsewhere. The other is that panspermia tends sometimes to excite even the most respectable adherents to levels of speculation that can be safely called imprudent. Francis Crick, co-discoverer of the structure of DNA, and his colleague Leslie Orgel have suggested that Earth was “deliberately seeded with life by intelligent aliens,” an idea that Gribbin calls “at the very fringe of scientific respectability”—or, put another way, a notion that would be considered wildly lunatic were it voiced by anyone other than a Nobel laureate. Fred Hoyle and his colleague Chandra Wickramasinghe further eroded enthusiasm for panspermia by suggesting, as noted in Chapter 3, that outer space brought us not only life but also many diseases such as flu and bubonic plague, ideas that were easily disproved by biochemists.
