One afternoon they both joined me in the laboratory, at my request, to learn a little more. A quiet word from Geordie to Ian made sure that we weren't going to be interrupted.
Geordie picked up a nodule which I'd cut in half – I had brought a few on board to help my explanation along.
He pointed to the white central core.
'I suppose you'll tell me again that it's a shark's tooth in the middle of this rock. You never did get around to explaining that, did you?'
I smiled and held up the stone. That's right, it is.'
'You're kidding.'
'No I'm not – it happens often. You see, a shark dies and its body drifts down; the flesh rots or is eaten, the bones dissolve – what bones a shark has, it's cartilage really – and by the time anything reaches the very bottom there's nothing left but the teeth. They are made of sodium triphosphate and insoluble in water. There are probably millions of them on any ocean bottom.'
I opened a small box. 'Look here,' I said and gave him a larger white bone. It was as big as the palm of his hand and curiously convoluted.
'What's this?'
'It's a whale's earbone,' said Bill, looking over his shoulder. 'I've seem 'em before.'
'Right, Bill. Also made of sodium triphosphate. We sometimes find them at the core of larger nodules – but more often it's a shark's tooth and most frequently a bit of clay.'
'So the manganese sticks to the tooth. How long does it take to make a nodule?' Geordie asked.
'Estimates vary from one millimetre each thousand years to one millimetre each million years. One chap estimated that it worked out to one layer of atoms a day – which makes it one of the slowest chemical reactions known. But I have my own ideas about that.'
They both stared at me. 'Do you mean that if you find a nodule with a half-diameter often millimetres formed round a tooth that the shark lived ten million years ago? Were there sharks then?' Geordie asked in fascination.
'Oh yes, the shark is one of our oldest inhabitants.'
We talked a little more and then I dropped it. They had a lot to learn yet and it came best in small doses. And there was plenty of time for talk on this voyage. We headed south-south-west to cut through the Bahamas and the approach to the Windward Passage. Once in the Passage we kept as clear as possible of Cuba – once we came across an American destroyer on patrol, which did us the courtesy of dipping her flag, to which we reciprocated. Then there was the long leg across the Caribbean to Colon and the entrance to the Panama Canal.
By then we had done our testing. There were minor problems, no more than teething troubles, and generally I was happy with the way things were going. Stopping to dredge a little, trying out the winch and working out on-station routines, was an interesting change from what we had been doing and everyone enjoyed it, and we remained lucky with the weather. I got some nodules up but there was a lot of other material, enough to cloud the issue for everyone but Geordie. Among the debris of ooze, red clay and deposits we found enough shark's teeth and whale's earbone to give everyone on board a handful of souvenirs.
Both Geordie and Bill were becoming more and more interested in the nodules and wanted to know more about them, so I arranged for another lab. session with them one day. I'd been assaying, partly to keep my hand in and partly to check on the readiness of my equipment for the real thing.
'How did the Atlantic nodules turn out?' Geordie asked. On the whole he did the talking – Bill watched, listened and absorbed.
'Same old low quality stuff that's always pulled out in the Atlantic,' I said. 'Low manganese, low iron and hardly anything else except contaminants, clay and suchlike. That's the trouble in the Atlantic; there's too much sediment even on the Blake Plateau.'
'Why does manganese behave this way – why does it lump together?'
I laughed. 'You want me to give you a course of physical chemistry right now? All right, I'll explain it as simply as I can. Do you know what a colloid is?'
Two headshakes.
'Look. If you put a teaspoon of sugar into water you get a sugar solution – that is, the sugar breaks down right to the molecular level and mixes intimately with the water. In other words, it dissolves. Right?'
'Right.'
'Now what if you have a substance that won't dissolve in water but is divided into very fine particles, much smaller than can be seen in a regular microscope, and each particle is floating in the water? That's a colloid. I could whip you up a colloid which looks like a clear liquid, but it would be full of very small particles.'
'I see the difference,' Geordie said.
'All right. Now, for reasons that I won't go into now, all colloidal particles must carry an electric charge. These charges make the colloidal particles of manganese dioxide clump together in larger and larger units. They also tend to be attracted to any electrically conductive surfaces such as a shark's tooth or a bit of clay. Hence the nodules.'
'You mean,' said Bill slowly, 'that having broken down a long time before, the manganese is trying to get together again?'
'Pretty well just that, yes.'
'Where does the manganese come from in the first place -when it starts clumping, that is?'
'From the rivers, from underground volcanic fissures, from the rocks of the sea bottom. Fellows, the sea out there is a big chemical broth. In certain localized conditions the sea becomes alkaline and the manganese in the rocks leaches out and dissolves in the water… .'
'You said it doesn't dissolve.'
'Pure metallic manganese will dissolve as long as the conditions are right, and that's what chemists call a "reducing atmosphere". Just believe me, Geordie. Currents carry the dissolved manganese into "oxidising atmospheres" where the water is more acid. The manganese combines with oxygen to form manganese dioxide which is insoluble and so forms a colloid – and then the process goes on as I've described.'
He thought about that. 'What about the copper and nickel and cobalt and stuff that's in the nodules?'
'How does the milk get into the coconut?'
We all laughed, taking some of the schoolroom air out of the lab. 'Well, all these metals have certain affinities for each other. If you look at the table of elements you'll find they're grouped closely together by weight – from manganese, number twenty-five, to copper, number twenty-nine. What happens is that as the colloidal particles grow bigger they scavenge the other metals – entrap them. Of course, this is happening over a pretty long period of time.'
'Say a hundred million years or so,' said Geordie ironically.
'Ah well, that's the orthodox view.'
'You think it can happen faster than that?'
'I think it could happen fast,' 1 said slowly. 'Given the right conditions, though just what these conditions would be I'm not sure. Someone else doing research thought so too, though I haven't been able to follow his reasoning. And I have seen peculiarities that indicate rapid growth. Anyway that's one of the objects of this trip – to find out.'
What I didn't say in Bill's hearing was that the 'somebody' was Mark, nor that the peculiarities I had seen were contained in the prize nodule left from his collection. And there was something else I didn't talk about; the peculiarities that led to high-cobalt assay. I was beginning to grope towards a theory of nodule formation which, though still vague, might ease the way ahead. I was becoming anxious to know how Campbell's cipher expert had made out in translating Mark's diary.* 3*
Ten days after leaving the Blake Plateau we warped into the dockside at Panama. At last we were in the Pacific, all my goals a step nearer. Campbell was waiting for us, jumped spryly aboard and shook hands with me and Geordie, waving genially at the rest of the crew.