+++ 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 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.’
‘I’m just wondering,’ said Ponder, wishing he had a beard to stroke thoughtfully, ‘if perhaps they might … improve with keeping …’
TWENTY-FOUR
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 cyanobacteria. 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.
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.1
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 Günter Wächtershäuser’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: animals 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.2 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.
The within was the big leap forward, or at least the big slither. Within you can put the things you need to protect, like internal organs. In one sense, you are not part of the environment any more – there is a you as well. And, like someone who now has a piece of property of their very own, you can begin to make improvements.
This is a lie-to-children, but as lies go it is a good one.
Triploblasts played a crucial role in evolution, precisely because they did have internal organs, and in particular they could ingest food and excrete it. Their excreta became a major resource for other creatures; to get an interestingly complicated world, it is vitally important that shit happens.
But where did all those triploblasts come from? Were they an offshoot of the Ediacarans? Or did they come from something else that didn’t leave fossils?
It’s hard to see how they could have come from Ediacarans. Yes, an extra layer of tissue might have appeared, but as well as that extra layer you need a lot of organization to exploit it. That organization has to come from somewhere. Moreover, there were these occasional tantalizing traces of what might have been pre-Cambrian triploblasts – fossils not of worms, which would have clinched it, but of things that might have been trails made by worms in wet mud.
And then again, might not.
In February 1998, we found out.
The discovery depended upon where – and in this case how – you look for fossils. One way for fossils to form is by petrification. There is a poorly known type of petrification that can happen very fast – within a few days. T
he soft parts of a dead organism are replaced by calcium phosphate. Unfortunately for palaeontologists, this process works only for organisms that are about a tenth of an inch (2 mm) long. Still, some interesting things are that tiny. From about 1975 onwards scientists found wonderfully preserved specimens of tiny ancient arthropods – creatures like centipedes with many segments. In 1994 they found fossilized balls of cells from embryos – early stages in the development of an organism – and it is thought that these come from embryonic triploblasts. However, all of these creatures must have come after the Ediacarans. But in 1998 Shuhai Xiao, Yun Zhang, and Andrew Knoll discovered fossilized embryos in Chinese rock that is 570 million years old – smack in the middle of the Ediacaran era. And those embryos were triploblasts.
Forty million years before the Cambrian explosion, there were triploblasts on Earth, living right alongside those enigmatic Ediacarans.
We are triploblasts. Somewhere in the pre-Cambrian, surrounded by mouthless, organless Ediacarans, we came into our inheritance.
It used to be thought that life was a delicate, highly unusual phenomenon: difficult to create, easy to destroy. But everywhere we look on Earth we find living creatures, often in environments that we would have expected to be impossibly hostile. It’s beginning to look as if life is an extremely robust phenomenon, liable to turn up almost anywhere that’s remotely suitable. What is it about life that makes it so persistent?
Earlier we talked about two ways to get off the Earth, a rocket and a space elevator. A rocket is a thing that gets used up, but a space elevator is a process that continues. A space elevator requires a huge initial investment, but once you’ve got it, going up and down is essentially free. A functioning space elevator seems to contradict all the usual rules of economics, which look at individual transactions and try to set a rational price, instead of asking whether the concept of a price might be eliminated altogether. It also seems to contradict the law of conservation of energy, the physicist’s way of saying that you can’t get something for nothing. But, as we’ve seen, you can – by exploiting the new resources that become available once you get your space elevator up and running.
The Science of Discworld Revised Edition Page 21
