Magnetic materials found in ancient rocks show that every so often – about once every half a million years, but with no sign of regularity – the Earth’s magnetic field flips polarity, reversing magnetic north and south. We’re not sure exactly why, but mathematical models suggest that the magnetic field can exist in these two orientations, with neither of them being totally stable. So whichever one it’s in, it eventually loses stability and flips to the other one. The flips are rapid, taking about 5,000 years; the periods between flips are about a hundred times as long.
Most of the other planets have magnetic fields, and these can be even more complicated and difficult to explain than that of the Earth. We’ve still got a lot to learn about planetary magnetism.
One of the most dramatic features of our planet was discovered in 1912 but wasn’t accepted by science until the 1960s, and some of the most compelling evidence was left by those flips in the Earth’s magnetism. This is the notion that the continents are not fixed in place, but wander slowly over the surface of the planet. According to Alfred Wegener, the German who first publicized the idea, all of today’s separate continents were originally part of a single supercontinent, which he named Pangea (‘All-Earth’). Pangea existed about 300 million years ago.
Wegener surely wasn’t the first person to speculate along such lines, because he got the idea – in part, at least – from the curious similarity between the shapes of the coasts of Africa and South America. On a map the resemblance is striking. That wasn’t Wegener’s only source of inspiration, however. He wasn’t a geologist; he was a meteorologist, specializing in ancient climates. Why, he wondered, do we nowadays find rocks in regions with cold climates that were clearly laid down in regions with warm climates? And why, for that matter, do we nowadays find rocks in regions with warm climates that were clearly laid down in regions with cold climates? For example, remains of ancient glaciers 420 million years old can still be seen in the Sahara Desert, and fossil ferns are found in Antarctica. Pretty much everyone else thought that the climate must have changed: Wegener became convinced that the climate had stayed much the same, give or take the odd ice age, and the continents had shifted. Perhaps they’d been driven apart by convection in the mantle – he wasn’t sure.
This was considered a crazy idea: it wasn’t suggested by a geologist, and it ignored all sorts of inconvenient evidence, and the alleged fit between South America and Africa wasn’t all that good anyway, and – to top it all – there was no conceivable mechanism for carting continents around. Certainly not convection, which was too weak. Great A’Tuin may lug a planet around on its back, but that’s fantasy: in the real world, there seemed to be no conceivable way for it to happen.
We use the word ‘conceivable’ because a number of very bright and very reputable scientists were busily making one of the subject’s worst, and commonest, errors. They were confusing ‘I can’t see a way for this to happen’ with ‘There is no way for this to happen.’ One of them, it pains one of us to admit, was a mathematician, and a brilliant one, but when his calculations told him that the Earth’s mantle couldn’t support forces strong enough to move continents, it didn’t occur to him that the theories on which those calculations were based might be wrong. His name was Sir Harold Jeffreys, and he really should have been more imaginative, because it wasn’t just the shapes of the land on either side of the Atlantic that fitted. The geology fitted too, and so did the fossil record. There is, for example, a fossil beast called Mesosaurus. It lived 270 million years ago, and is found only in South America and Africa. It couldn’t have swum the Atlantic, but it could have evolved on Pangea and spread to both continents before they drifted apart.
In the 1960s, however, Wegener’s ideas became orthodox and the theory of ‘continental drift’ became established. At a meeting of leading geologists, a Ponder Stibbons-like young man named Edward Bullard and two colleagues enlisted the aid of a new piece of kit called a computer. They instructed the machine to find the best fit between Africa and South America, and North America, and Europe, allowing for a bit of breakage but not too much. Instead of using today’s coastline, which was never a very sensible idea but made it possible to claim that the fit wasn’t actually that good, they used the contour corresponding to a depth of 3200 feet (1000 m) underwater, whose shape is less likely to have been changed by erosion. The fit was good, and the geology across the join matched amazingly well. And even though the people at the conference came out just as divided in their opinions as they’d been when they went in, somehow continental drift had become the consensus.
Today we have much more evidence, and a fair idea of the mechanism. Down the middle of the Atlantic Ocean, and elsewhere in other oceans, there runs a ridge – roughly north–south and about midway between South America and Africa. Volcanic material is welling up along that ridge, and spreading sideways. It’s been spreading for 200 million years, and it’s still doing it today: we can even send deep-sea submarines down there to watch. It’s not spreading at speeds humans can see – America moves about three-quarters of an inch (2 cm) further away from Africa every year, about the same rate that your fingernails grow – but today’s instruments can easily measure such a change.
The most striking evidence for continental drift is magnetic: the rocks on either side bear a curious pattern of magnetic stripes, reversing polarity from north to south and back again, and that pattern is symmetric on either side of the ridge – making it clear that the stripes were frozen in place as the rocks cooled in the Earth’s magnetic field. Whenever the Earth’s dynamo flipped polarity, as it does from time to time, the rock immediately adjacent to the ridge-line, on either side, got the same new polarity. As the rocks then spread apart, they took the same patterns of stripes with them.
The surface of the Earth is not a solid sphere. Instead, the continents and the ocean-beds float on top of large, essentially solid plates, and those plates can be driven apart by upwelling magma. (Oh, but mostly by convection in the mantle. Jeffreys didn’t know what we now know about how the mantle moves.) There are about a dozen plates, ranging from 600 miles (1000 km) across to 6000 miles (10,000 km), and they twist and turn. Where plate boundaries rub against each other, sticking and slipping and sticking and slipping, you get a lot of earthquakes and volcanoes. Especially along the ‘Pacific rim’, the edge of the Pacific Ocean up along the west coast of Chile, central America, the USA, along down past Japan, and back round New Zealand, which is all the edge of a single gigantic plate. Where plate boundaries collide you get mountain ranges: one plate burrows under the other, lifting it up and crushing and folding its edges. India was once not part of the main Asian continent at all, but came crashing into it, creating the world’s highest mountain range, the Himalayas. India hasn’t fully stopped even now, and the Himalayas are still being pushed up by the force of the impact.
SEVENTEEN
SUIT OF SPELLS
A FIGURE WAS Frogmarched through the early-morning corridors, surrounded by the senior wizards. It wore a long white nightshirt, and a nightcap with the word ‘Wizzard’ embroidered, inexpertly, on it. It was Unseen University’s least qualified but most well-travelled member, usually away from something. And it was in trouble.
‘This won’t hurt a bit,’ said the Senior Wrangler.
‘It’s right up your street,’ said the Lecturer in Recent Runes.
‘It’s on a log and in your face,’ explained the Dean.
‘That isn’t what HEX said, is it?’ said the Senior Wrangler, as the sleepy figure was hustled around a corner.
‘Very similar, but what HEX said made less sense,’ said the Dean.
They hurried across the lawn and barged through the doors in the High Energy Magic Building.
Mustrum Ridcully finished filling his pipe, and struck a match on the dome of the Project. Then he turned, and smiled.
‘Ah, Rincewind,’ he said. ‘Good of you to come.’
‘I was dragged, sir.’
‘Well done. A
nd I have good news. I intend to appoint you Egregious Professor of Cruel and Unusual Geography. The post is vacant.’
Rincewind looked past him. On the far side of the room some of the junior wizards were working in a haze of magic that made it hard to see exactly what it was they were working on, but it looked almost like … some sort of skeleton.
‘Oh,’ he said. ‘Er … but I’m very happy as assistant librarian. I’m getting really good at peeling the bananas.’
‘But the new post offers you room, board and all your laundry done,’ said the Archchancellor.
‘But I get that already, sir.’
Ridcully drew leisurely on his pipe and blew out a cloud of blue smoke.
‘Up until now,’ he said.
‘Oh. I see. And you’re about to send me somewhere really dangerous, yes?’
Ridcully beamed. ‘How did you guess?’
‘It wasn’t a guess.’
Fortunately the Dean had been forewarned and had grabbed the back of Rincewind’s nightshirt, and so he was ready. The wizard’s bedroom slippers skidded uselessly on the tiles as he tried to make for the door.
‘It’s best to let him run for a little while,’ said the Senior Wrangler. ‘It’s a nervous reaction.’
‘And the best thing is,’ said Ridcully, to Rincewind’s back, ‘that although we are sending you to a place of immense danger where no living thing could possibly survive, you will not, in so many words, actually be there. Won’t that be nice?’
Rincewind hesitated.
‘How many words?’
‘It’ll be like being in a … story,’ said the Archchancellor. ‘Or … or a dream, as far as I can understand it. Mister Stibbons! Come and explain!’
‘Oh, hello, Rincewind,’ said Ponder, stepping out of the mist and wiping his hands on a rag. ‘Twelve spells HEX has amalgamated for this! It’s an amazing piece of thaumaturgical engineering! Do come and see!’
There are creatures which have evolved to live in coral reefs and simply could not survive in the rough, tooth-filled wastes of the open sea. They continue to exist by lurking among the dangerous tentacles of the sea anemone or around the lips of the giant clam and other perilous crevices shunned by all sensible fish.
A university is very much like a coral reef. It provides calm waters and food particles for delicate yet marvellously constructed organisms that could not possibly survive in the pounding surf of reality, where people ask questions like ‘Is what you do of any use?’ and other nonsense.
In fact Rincewind in his association with UU had survived dangers that would have stripped a hero to the bone, but he nevertheless believed, despite all the evidence to the contrary, that he was safe in the university. He would do anything to stay on the roll.
At the moment this involved looking at some sort of skeletal armour made out of smoke while Ponder Stibbons gabbled incomprehensible words in his ear. As far as he could understand it, the thing put all your senses somewhere else when you stayed here. So far, that sounded quite acceptable, since it had always seemed to Rincewind that if you had to go a long way away it’d be nice to stay at home while you did it, but people seemed a little unclear about where pain fitted in.
‘We’ll send you – that is, your senses – somewhere,’ said Ridcully.
‘Where?’ said Rincewind.
‘Somewhere amazing,’ said Ponder. ‘We just want you to tell us what you see. And then we’ll bring you back.’
‘At what point will things go wrong?’ said Rincewind.
‘Nothing can possibly go wrong.’
‘Oh,’ Rincewind sighed. There was no point in arguing with a statement like that. ‘Could I have some breakfast first?’
‘Of course, dear fellow,’ said Ridcully, patting him on the back. ‘Have a hearty meal!’
‘Yes, I thought that’d probably be the case,’ said Rincewind gloomily.
When he’d been taken away, under escort by the Dean and a couple of college porters, the wizards clustered around the project.
‘We’ve found a suitably large “sun”, sir,’ said Ponder, taking care to annunciate the inverted commas. ‘We’re moving the world now.’
‘A very suspicious idea, this,’ said the Archchancellor. ‘Suns go around. We see it happen every day. It’s not some kind of optical illusion. This is a bit of a house of cards we’re building here.’
‘It’s the only one available, sir.’
‘I mean, things fall down because they’re heavy, you see? The thing that causes them to fall down because they’re heavy is, in fact, the fact that they’re heavy. ‘Heavy’ means inclined to fall down. And, while you can call me Mr Silly –’
‘Oh, I wouldn’t do that, sir,’ Ponder said, glad that Ridcully couldn’t see his face.
‘– I somehow feel that a crust of rock floating around on a ball of red-hot iron should not be thought of as “solid ground”.’
‘I think, sir, that this universe has a whole parcel of rules that take the place of narrativium,’ said Ponder. ‘It’s … sort of … copying us, as you so perspicaciously pointed out the other day. It’s making the only kind of suns that can work in it, and the only worlds that can exist if you don’t have chelonium.’
‘Even so … going around a sun … that’s the sort of thing the Omnian priests used to teach, you know. Mankind is so insignificant that we just float around on some speck, and all that superstitious stuff. You know they used to persecute people for saying the turtle existed? And any fool can see it exists.’
‘Yes, sir. It certainly does.’
There were problems, of course
‘Are you sure it’s the right sort of sun?’ said Ridcully.
‘You told HEX to find one that was “nice and yellow, nice and dull, and not likely to go off bang”, sir,’ said Ponder. ‘It seems to be a pretty average one for this universe.’
‘Even so … tens of millions of miles … that’s a long way away for our world.’
‘Yes, sir. But we tried some experimental worlds close to and they fell in, and we tried one a bit further out and that’s baked like a biscuit, and there’s one … well, it’s a bit of an armpit, really. The students have got quite good at making different sorts. Er … we’re calling them planets.’
‘A planet, Stibbons, is a lump of rock a mere few hundred yards across which gives the night sky a little, oh, I don’t know, what’s the word, a little je ne sais quoi –’
‘These will work, sir, and we’ve such a lot of them. As I said, sir, I’ve come to agree with your theory that, within the Project, matter is trying to do all by itself what in the real world is done by purpose, probably conveyed via narrativium.’
‘Was that my theory?’ said Ridcully.
‘Oh, yes, sir,’ said Ponder, who was learning the particular survival skills of the academic reef.
‘It sounds rather a parody to me, but I dare say we will understand the joke in time. Ah, here comes our explorer. ‘Morning, Professor,’ said Ridcully. ‘Are you ready?’
‘No,’ said Rincewind.
‘It’s very simple,’ said Ponder, leading the reluctant traveller across the floor. ‘You can think of this assemblage of spells as a suit of very, very good armour. Things will flicker, and then you’ll be … somewhere else. Except you’ll really be here, you see? But everything you see will be somewhere else. Absolutely nothing will hurt you because HEX will buffer all extreme sensations and you’ll simply receive a gentle analogue of them. If it’s freezing you’ll feel rather chilly, if it’s boiling you’ll feel a little hot. If a mountain falls on you it’ll be a bit of a knock. Time where you’re going is moving very fast but HEX can slow it down while you are there. HEX says that he can probably exert small amounts of force within the Project, so you will be able to lift and push things, although it will feel as though you’re wearing very large gloves. But this should not be required because all we want you to do to start with … Professor … is tell us what you see.’
Rincewind looke
d at the suit. It was, being largely make up of spells under HEX’s control, shimmery and insubstantial. Light reflected off it in odd ways. The helmet was far too large and completely covered the face.
‘I have three … no, four … no, five questions,’ he said.
‘Yes?’
‘Can I resign?’
‘No.’
‘Do I have to understand anything you just told me?’
‘No.’
‘Are there any monsters where I’m being sent?’
‘No.’
‘Are you sure?’
‘Yes.’
‘Are you totally positive about that?’
‘Yes.’
‘I’ve just thought of another question,’ said Rincewind.
‘Fire away.’
‘Are you really sure?’
‘Yes!’ snapped Ponder. ‘And even if there were any monsters, it wouldn’t matter.’
‘It’d matter to me.’
‘No it wouldn’t! I have explained! If some huge toothed beast came galloping towards you, it’d have no effect on you at all.’
‘Another question?’
‘Yes?’
‘Is there a toilet in this suit?’
‘No.’
‘Because there will be if a huge toothed beast comes galloping towards me.’
‘In that case, you just say the word and you can come back and use the privy down the hall,’ said Ponder. ‘Now, stop worrying, please. These gentlemen will help you, er, insert yourself into the thing, and we’ll begin …’
The Archchancellor wandered up as the reluctant professor was enveloped in the glittering, not-quite-there stuff.
‘A thought occurs, Ponder,’ he said.
‘Yes, sir?’
‘I suppose there’s no chance that there is life anywhere in the Project?’
Ponder looked at him in frank astonishment.
‘Absolutely not, sir! It can’t happen. Simple matter is obeying a few rather odd rules. That’s probably enough to get things … spinning and exploding and so on, but there’s no possibility that they could cause anything so complex as –’
The Science of Discworld Revised Edition Page 16