The Science of Discworld I tsod-1

by Terry Pratchett

  'But we've done so many things...'

  'Just moved things around, sir.'

  'Seems a shame to have made a world and there's no one to live on it,' said the Senior Wrangler.

  'When I was small, I had a model farmyard,' said the Bursar, looking up from his reading.

  'Thank you, Bursar. Very interesting,' said the Archchancellor. 'All right, let's play by the rules. What do you have to move around to get people?'

  'Well ... bits of other people, my father told me,' said the Dean.

  'Bad taste there, Dean.'

  'Many religions start with dust,' said the Senior Wrangler. 'And then you bring it alive in some way.'

  'That's pretty hard even with magic,' said the Archchancellor. 'And we can't use magic.'

  'Up in Nothingfjord they believe that all life was created when the god Noddi cut off his ... unmentionables and hurled them at the sun, who was his father,' said the Senior Wrangler.

  'What, you mean his ... underwear?' said the Lecturer in Recent Runes, who could be a bit slow.

  'First of all we can't physically exist inside the Project, secondly that sort of thing is unhygienic, and thirdly I doubt very much if you'll find a volunteer,' said the Archchancellor sharply. 'Anyway, we're men of magic. That is superstition.'

  'Can we make weather, then?' said the Dean.

  'I think HEX can let us do that,' said Ponder. 'Weather is only pushing stuff around.'

  'So we can aim lightning at anyone we don't like?'

  'But there isn't anyone on the world, whether we like them or not,' said Ponder wearily. 'That's the point.'

  'And while the Dean can make enemies anywhere, I think that, ah, Roundworldwould test even his powers,' said Ridcully.

  'Thank you, Archchancellor'

  'Happy to oblige, Dean.'

  HEX's keyboard clattered. The quill pen began to write.

  It began:

  +++ I Don't Think You Are Going To Believe This +++

  Thunderstorms tore the air apart, far out to sea.

  The air blinked. The storm was gone. The shoreline looked dif­ferent.

  'Hey, what happened?' said Rincewind.

  'Everything all right?' said Ponder Stibbons in his ear.

  'What happened just then?'

  'We've moved you forward in time a little,' said Ponder The tone of his voice suggested that he dreaded being asked why.

  'Why?' said Rincewind.

  'You'll laugh when I tell you this ...'

  'Oh, good. I like a laugh.'

  'HEX says he's detecting life all round you. Can you see any­thing?'

  Rincewind looked around warily. The sea was sucking at the shore, which had a bit of sand on it now. Scum rolled in the waves.

  'No,' he said.

  'Good. You see, there can't be any life where you are,' Ponder went on.

  'Where am I exactly?'

  'Er ... a sort of magical world with no one in it but yourself'

  'Oh, you mean the sort everyone lives in,' said Rincewind bit­terly. He glanced at the sea again, just in case.

  'But if you wouldn't mind having a look ...' Ponder went on.

  'For this life that can't possibly exist?'

  'Well, you are the Professor of Cruel and Unusual Geography.'

  'It's the cruel and unusual geography that's bothering me,' said Rincewind. 'Incidentally, have you looked at the sea lately? It's blue.'

  'Well? The sea is blue.'

  'Really?'

  The omniscope was once again the centre of attention.

  'Everyone knows the sea is blue,' said the Dean. 'Ask anyone.'

  'That's right,' said Ridcully. 'However, while everyone knows the sea is blue, what everyone usually sees is a sea that's grey or dark green. Not this colour. This is virulent!'

  'I'd say turquoise,' said the Senior Wrangler.

  'I used to have a shirt that colour,' said the Bursar.

  'I thought it might be copper salts in the water,' said Ponder Stibbons. 'But it isn't.'

  The Archchancellor picked up HEX's latest write-out. It read:

  +++ Out Of Cheese Error +++

  'Not helpful,' he muttered.

  'Thank goodness he's still operating the Project,' said Ponder, joining him. 'I think he's got confused.'

  'It's not his job to be confused,' said Ridcully. 'We don't need a machine for being confused. We're entirely capable of confusin'

  ourselves. It is a human achievement, confusion, and right at this minute I feel I am winning a prize. You, Mister Stibbons, said there was no possibility of life turnin' up inside the Project.'

  Ponder waved his hands frantically. 'There's no way that it can! Life isn't like rocks and water. Life is special!'

  The breath of gods, that sort of thing?' said Ridcully.

  'Not gods as such, obviously, but...'

  'I suppose from the point of view of rocks, rocks are special,' said Ridcully, still reading HEX's output.

  'No, sir. Rocks don't have a point of view.'

  Rincewind lifted up a shard of rock, very carefully, ready to drop it immediately at the merest suggestion of tooth or claw.

  'This is silly,' he said. 'There's nothing here.'

  'Nothing?' said Ponder, inside the helmet.

  'Some of the rocks have got all kind of yuk on them, if that's your idea of a good time.'

  'Yuk?'

  'You know ... gunge.'

  'HEX seems to be suggesting now that whatever is showing up is, and is not, life,' said Ponder, a man whose interest in slime was lim­ited.

  'That's very cheering.'

  'There seems to be a particular concentration not far from you ... we're just going to move you so that you can have a look at it...'

  Rincewind's head swam. A moment later, the rest of his body wanted to join it. He was underwater.

  'Don't worry,' said Ponder, 'because although you're at a very great depth, the pressure can't possibly hurt you.'

  'Good.'

  'And the boiling water should feel merely tepid.'

  'Fine.'

  'And the terrible upflow of poisonous minerals can't harm you because of course you're not really there.'

  'So, all in all, I'm laughing,' said Rincewind gloomily, peering at the dim glow ahead of him.

  'It's gods, definitely,' said the Archchancellor. 'Gods have turned up while our back was turned. There can be no other explanation.'

  'Then they seem rather unambitious,' sniffed the Senior Wrangler. 'I mean, you'd expect humans, wouldn't you? Not ... blobs you can't see. They're not going to bow down and worship anyone, are they?'

  'Not where they are,' said Ridcully. 'The planet's full of cracks! You shouldn't get fire under water. That's against nature!'

  'Everywhere you look, little blobs,' said the Senior Wrangler. 'Everywhere.'

  'Blobs,' said the Lecturer in Recent Runes. 'Can they pray? Can they build temples? Can they wage holy war on less enlightened blobs?'

  Ponder shook his head sadly. hex's results were quite clear. Nothing solid could cross the barrier into Roundworld. It was pos­sible, with enough thaumic effort, to exert tiny pressures, but that was all. Of course, you could speculate that thought might get in there, but if that was the case the wizards were thinking some very dull thoughts indeed. 'Blobs' wasn't really a good word for what were currently floating in the warm seas and dribbling over the rocks. It had far too many overtones of feverish gaiety and excite­ment.

  'They're not even moving,' said Ridcully. 'Just bobbing about.'

  'Blobbing about, haha,' said the Senior Wrangler.

  'Could we ... help them in some way?' said the Lecturer in Recent Runes. 'You know ... to become better blobs? I fear we have some responsibility.'

  'They may be as good as blobs get,' said Ridcully. 'What's up with that Rincewind fellow?'

  They turned. In its circle of smoke, the suited figure was mak­ing frantic running motions.

  'Do you think, on reflection, that it might not have good idea to mi
niaturize his image in Roundworld?' said Ridcully.

  'It was the only way we could get him into that little rock pool HEX wanted us to look at, sir,' said Ponder. 'He doesn't have to be any particular size. Size is relative.'

  'Is that why he keeps calling out for his mother?'

  Ponder went over to the circle and rubbed out a few important runes. Rincewind collapsed on the floor.

  'What idiot put me in there? he said. 'Ye gods, it's awful! The size of some of those things!'

  'They're actually tiny,' said Ponder, helping him up.

  'Not when you are smaller than them!'

  'My dear chap, they can't possibly hurt you. You have nothing to fear but fear itself'

  'Oh, is that so? What help is that? You think that makes it better? Well, let me tell you, some of that fear can be pretty big and nasty...'

  'Calm down, calm down?'

  'Next time I want to be big, understand?'

  'Did they try to communicate with you in any way?'

  'They just flailed away with great big whiskers! It was worse than watching wizards arguing!'

  'Yes, I doubt if they are very intelligent.'

  'Well, nor are the rock pool creatures.'

  Tin just wondering,' said Ponder, wishing he had a beard to stroke thoughtfully, 'if perhaps they might ... improve with keep­ing ...'

  24. DESPITE WHICH ...

  THAT BLUE IN THE ROUNDWORLD SEA isn't a chemical, well, not in the usual Simple chemical' sense of the word. It's a mass of bacteria, called cyanobac-teria. Another name for them is 'blue-green algae', which is wonderfully confusing. Modern so-called blue-green algae are usually red or brown, but the ancient ones probably were blue-green. And blue-green algae are really bac­teria, whereas most other algae have cells with a nucleus and so are not bacteria. The blue-green colour comes from chlorophyll, but of a different kind from that in plants, together with yellow-orange chemicals called carotenoids.

  Bacteria appeared on Earth at least 3.5 billion years ago, only a few hundred million years after the Earth cooled to the point at which living creatures could survive on it. We know this because of strange layered structures found in sedimentary rocks. The layers can be flat and bumpy, they can form huge branched pillars, or they can be highly convoluted like the leaves in a cabbage. Some deposits are half a mile thick and spread for hundreds of miles. Most date from 2 billion years ago, but those from Warrawoona in Australia are 3.5 billion years old.

  To begin with, nobody knew what these deposits were, In the 1950s and 1960s they were revealed as traces of communities of bacteria, especially cyanobacteria.

  Cyanobacteria collect together in shallow water to form huge, floating mats, like felt. They secrete a sticky gel as protection against ultraviolet light, and this causes sediment to stick to the mats. When the layer of sediment gets so thick that it blocks out the light, the bacteria form a new layer, and so on. When the layers fossilize they turn into stromatolites, which look rather like big cushions. The wizards haven't been expecting life. Roundworld runs on rules, but life doesn't, or so they think. The wizards see a sharp discontinuity between life and non-life. This is the problem of expecting becomings to have boundaries, of imagining that it ought to be easy to class all objects into either the category 'alive' or the category 'dead'. But that's not possible, even ignoring the flow of time, in which 'alive' can become 'dead', and vice versa. A 'dead' leaf is no longer part of a living tree, but it may well have a few revivable cells.

  Mitochondria, now the part of a cell that generates its chemical energy, once used to be independent organisms. Is a virus alive? Without a bacterial host it can't reproduce, but neither can DNA copy itself without a cell's chemical machinery.

  We used to build 'simple' chemical models of living processes, in the hope that a sufficiently complex network of chemistry could 'take off', become self-referential, self-copying, by itself There was the concept of the 'primal soup', lots of simple chemicals dis­solved in the oceans, bumping into each other at random, and just occasionally forming something more complicated. It turns out that this isn't quite the way to do it. You don't have to work hard to make real-world chemistry complex: that's the default. It's easy to make complicated chemicals. The world is full of them. The problem is to keep that complexity organized.

  What counts as life? Every biologist used to have to learn a list of properties: ability to reproduce, sensitivity to its environment, utilization of energy, and the like. We have moved on. 'Autopoeisis', the ability to make chemicals and structures related to one's own reproduction, is not a bad definition, except that modern life has evolved away from those early necessities. Today's biologists prefer to sidestep the issue and define life as a property of the DNA mol­ecule, but this begs the deeper question of life as a general type of process. It may be that we're now defining life in the same way that 'science fiction' is defined, it's what we're pointing at when we use the term[34].

  The idea that life could somehow be self-starting is still contro­versial to many people. Nevertheless, it turns out that finding plausible routes to life is easy. There must be at least thirty of them.

  It's hard to decide which, if any, was the actual route taken, because later lifeforms have destroyed nearly all the evidence. This may not matter much: if life hadn't taken the route that it did, it could eas­ily have taken one of the others, or one of the hundred we haven't thought of yet.

  One possible route from the inorganic world to life, suggested by Graham Cairns-Smith, is clay. Clay can form complicated micro­scopic structures, and it often 'copies' an existing structure by adding an extra layer to it, which then falls off and becomes the starting point of a new structure. Carbon compounds can stick on to clay surfaces, where they can act as catalysts for the formation of complex molecules of the kind we see in living creatures, proteins, even DNA itself. So today's organisms may have hitched an evolu­tionary ride on clay.

  An alternative is Gunther Wachterhauser's suggestion that pyrite, a compound of iron and sulphur, could have provided an energy source suitable for bacteria. Even today we find bacteria miles underground, and near volcanic vents at the bottom of the oceans, which power themselves by iron/sulphur reactions. These are the source of the 'upflow of poisonous minerals' noticed by Rincewind. It's entirely conceivable that life started in similar envi­ronments.

  A potential problem with volcanic vents, though, is that every so often they get blocked, and another one breaks out somewhere else. How could the organisms get themselves safely across the interven­ing cold water? In 1988 Kevin Speer realized that the Earth's rotation causes the rising plumes of hot water from vents to spin, forming a kind of underwater hot tornado that moves through the deep ocean. Organisms could hitch a ride on these. Some might make it to another vent. Many would not, but that doesn't matter -all that would be required would be enough survivors.

  It is interesting to note that back in the Cretaceous, when the seas were a lot warmer than now, these hot plumes could even have risen to the ocean's surface, where they may have caused 'hyper-canes', like hurricanes but with a windspeed close to that of sound. These would have caused major climatic upheavals on a planet which, as we shall see, it not the moderately peaceful place we tend to believe it is.

  Bacteria belong to the grade of organisms known as prokaryotes. They are often said to be 'single-celled', but many single-celled creatures are far more complex and very different from bacteria. Bacteria are not true cells, but something simpler; they have no cell wall and no nucleus. True cells, and creatures both single-celled and many-celled, came later, and are called eukaryotes. They probably arose when several different prokaryotes joined forces to their mutual benefit, a trick known as symbiosis. The first fossil eukary­otes are singe-celled, like amoebas, and appear about 2 billion years ago. The first fossils of many-celled creatures are algae from 1 bil­lion years ago ... maybe even as old as 1.8 billion years.

  This was the story as scientists understood it up until 1998: ani­m
als like arthropods and other complex beasts came into being a mere 600 million years ago, and that until about 540 million years ago the only creatures were very strange indeed, quite unlike most of what's around today.

  These creatures are known as Ediacarans, after a place in Australia where the first fossils were found[35]. They could grow to half a metre or more, but as far as can be told from the fossil record, seem not to have had any internal organs or external orifices like a mouth or an anus (they may have survived by digesting symbiotic bacteria in their selves, or by some other process we can only guess at). Some were flattened, and clustered together in quilts. We have no idea whether the Ediacarans were our distant ancestors, or whether they were a dead end, a lifestyle doomed to failure. No matter: they were around then, and as far as anyone knew, not much else was. There are hints of fossil wormcasts, though, and some very recent fossils look like ... but we're getting ahead of the story. The point is that nearly all Ediacaran life was apparently unrelated to what came later.

  About 540 million years ago the Pre-Cambrian Ediacarans were succeeded by the creatures of the Cambrian era. For the first ten million years, these beasties were also pretty weird, leaving behind fragments of spines and spikes which presumably are the remains of prototype skeletons that hadn't yet joined up. At that point, nature suddenly learned how to do joined-up skeletons, and much else: this was the time known as the Cambrian Explosion. Twenty mil­lion years later virtually every body-plan found in modern animals was already in existence: everything afterwards was mere tinkering. The real innovation of the Cambrian Explosion, though, was less obvious than joined-up skeletons or tusks or shells or limbs. It was a new kind of body plan. Diploblasts were overtaken by triploblasts ...

  Sorry, Archchancellor. We mean that creatures began to put another layer between themselves and the universe. Ediacarans and modern jellyfish are diploblasts, two-layered creatures. They have an inside and an outside, like a thick paper bag. Three-layered crea­tures like us and practically everything else around are called triploblasts. We have an inner, an outer, and a within.