Carbon – the stuff of life we’re shamefully ignorant about

26 May 2018

9:00 AM

26 May 2018

9:00 AM

‘I didn’t realise we were carbon,’ said a friend to whom I mentioned this book. She was the first of several. It’s odd to think of clever and educated people not knowing that we are made of such stuff. But The Many Lives of Carbon is an odd book to come to grips with. Its title promises plain speaking about carbon, which the book then delivers. Nothing to lose sleep over. Yet one does.

This is partly because it mines a rich seam. I fell asleep thinking about the carboniferous period, and dreamt I was one of the seven dwarfs, trapped underground with a pickaxe and a vile hod, and woke myself up with a sepulchral groan of horror, which woke the dog, and there was nothing for it but to go downstairs and put the kettle on.

The thing about the book, I realised in the kitchen, was that the loop — the carbon loop — is all-entwining. Where do you start? Cellular processes? The cultural history of the diamond (protection against plague)? The Krebs cycle? Or just the kitchen, warm because of the central heating, which was gas-powered, which was carbon. The kettle was electric, which came from a carbon-fuelled power station. The tea was a carbon-based life form, now dead, and the dog was a carbon-based life form, alive and singing cheerfully. I was writing in my notebook with a pencil, which is graphite, which is carbon, and I was doing so in my role as another carbon-based life form, though not singing. Indeed, while it’s possible to imagine another sort of life form, non-carbon-based (replication and, arguably, random mutation are the two necessary behaviours for the diagnosis of life), it’s hard to do it without the echo of Scotty murmuring: ‘It’s life, Jim, but not as we know it.’

Carbon is ubiquitous and uniquely gifted. It is perversely polymorphous — graphite, diamond and fullerene, that last one particularly and marvellously improbable: a sort of geodetic football, 60 carbon atoms wired gleefully together, as if by a subatomic version of Buckminster Fuller, hence the name.

It is also wildly sociable, flexibly poly-valent like an atomic #MeToo Playboy mansion sex kitten: bonds forming, reforming, circling (the famous ourobouros of the benzene ring) and, when the action requires it, bonding with itself. Its capacity to bond and form multiple long chains — those polymers which have transformed our lives in the last century — are unique. Without it all, no life. Without at all, too, no energy, since each one of those bonds stores energy from the sunshine of 350 million years ago, recoverable on demand and, it turns out, at possibly too high a price.

Dag Olav Hessen subtly lays out his treatise on this, the only element to have an entire branch of chemistry devoted to its exploits. He touches on fire and plastic, on the truth (spotted first by Aristotle) that we are all freeloading on the labour of the photosynthesisers: they are the ones who harvest those photons from the light of the sun; we just eat the buggers. If we’re really smart, we eat the buggers who eat the buggers. There’s the food chain, which is also a carbon chain, and it will probably be the death of us.

With excursions into, among others, the distant registers of Leibig’s Bucket, methane and carbon-dating, the infrastructural knife slips in: the ‘long carbon cycle’, more compelling methane, the evolution of oxygen, a detour into the crucial matter of nitrogen and phosphorus (starring recently in the organophosphate grand guignol in Salisbury) and we are swept up into the, by now clearly inexorable, nexus of ‘petro-holism’ and man-made climate change.

And all of it, carbon. But the trouble is, carbon is chemistry. Even if you do chemistry to university level, it’s oddly evanescent. You get it for a bit, and then, unless you use it all the time, it goes. The words and processes come readily enough to mind — cis-this and laevo-that, isotopes and double-bonds, methylation and (crucial in life sciences) oxidative stress — but the underlying concepts blur and fade. The memory and the understanding coarsen.

But what remains is the picture of carbon as the enthusiastic courtesan of the periodic table. Tucked up nicely in the top right-hand corner, carbon, with its six electrons, is happy to bond with other atoms but equally happy, like a molecular peep-show, to bond enthusiastically with itself. Phosphorus, nitrogen, chlorine, oxygen and, of course, hydrogen are all grist to its polyamorous nature. It’s a clue to carbon’s pre-eminence that all but its simplest relationships, like CO2, are clustered under the tremendous but accurate term ‘organic chemistry’. Without carbon, we are not. The single most important chemical reaction, and the basis of life itself, requires just three elements: carbon, hydrogen and oxygen. It’s this:

6CO2 + 12H2O + energy –› C6H12O6 + 6O2 + 6H2O

That’s to say, six molecules of carbon dioxide plus 12 molecules of water plus energy (sunlight, where all our energy comes from, early or late) is transformed into one molecule of glucose, six of oxygen and six of water. The exhaust from this process is oxygen (hurrah!) and water (hurrah!). Where does the energy go? Crudely speaking, into the glucose. This is what plants do. Then we eat them. We should, I suppose, earnestly hope that the plants don’t wise up.

That, though, conceals a huge amount of complex electron transport in the almost impenetrable process of photosynthesis. I know one scientist who has spent most of her career working on one transport of one electron in one stage of the photosynthetic chain. It throws a sharp light on the problem Hessen faces: how much to explain. If he explained everything, there would be no room for the actual book he is writing. On the other hand, he doesn’t there and then identify the glucose molecule. He doesn’t explain quite a lot. Look for valency or double-bonds, for example, and you will have a struggle.

But there is no reason why a book should contain everything you need to read it. Not now that we have smartphones. Even school-level chemistry should do the trick with your pocket-sized supercomputer beside you, tuned to Wikipedia.

It is worth it, to unearth the story Hessen tells. That he has pitched his text to require a bit of work by the non-specialist is a good call. That cognitive load will clarify this tricky but compelling exposition far better than any microwaveable polemic. But be prepared to lose a little sleep puzzling out. And then rather more sleep thinking about his conclusions.

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