Terry Pratchett - The Science of Discworld I

'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 miniaturize 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 ...'

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] Everyone knows what science fiction is - until you start asking questions like 'Is a book set five years in the future automatically SF? Is it SF just because it's set on another world, or is it simply fantasy with nuts and bolts on the out­side? Is it SF if the author thinks it isn't? Does it have to be set in the future? Does the presence of Doug McClure mean that a movie is SF, or merely that the men-in-rubber-monster-suits quotient is going to be high?' One of the best SF books ever written was the late Roy Lewis's The Evolution Man; there is no technology in it more sophisticated than a bow, it's set in the far past, the characters are barely more than ape-men ... but it is science fiction, nonethe­less. .