Alan Smith: the first computer aided fit of the continents

Alan Smith comments on maps of former positions of the continents either side of the Atlantic Ocean, made in the 1960s, aided by a computer program.

My name’s Alan Smith. I’m a retired member of the Department of Earth Sciences, which used to be the Department of Geology, in Cambridge, although I started my scientific career up at what is now known as Bullard Labs, where I joined as a research assistant with Bullard and Jim Everett and Jack Miller. In particular, the work I did with Everett and Bullard became well known. It was essentially making maps of where the continents were like 200 or so million years ago, though we didn’t know it at the time. But we made the first, or Jim Everett in particular wrote a programme that made the first computer fit of South America and Africa, and I came along, joined the North Atlantic continent together, and then we joined both of them together so we had a fit of the circum Atlantic continents, which is one of the pieces of work I suppose I’m well known for. So I’m rolling out this map, which really hasn’t been fully rolled for a number of years. It was made one of Teddy Bullard’s research students called Jim Everett, who wrote a programme to fit the edges of the continents together. Now what do we mean by the edge of the continents? This is the coastline, the present day coastline of South America, this is the present day coastline of Africa. But it’s not the edge of the continent. The edge of the continent is somewhere offshore, beyond the coastline, where it joins onto the ocean floor, and I think in this particular case, this is the I think 500 fathom line, which is about 1,000 metres depth. And visually you can see, despite Harold’s comments, it’s quite a good fit. He actually tried several contours, but I think the 500 fathom was the best fit. And it was unclear how to fit the northern continents together, the ones around the North Atlantic, because – now you have to be a little bit of a geologist to be able to make this map, because there are things that overlap and things that … where there are gaps, which have a geological reason, which we need to know about. So here we are, here’s Greenland, here’s Scandinavia, we are here, this is North America. And that is what I came up as a fit. Now if you know your geography you will realise that Iceland isn’t on this map. And the reason Iceland isn’t on this map, we understand today, is ‘cause it’s a huge hotspot area. But we didn’t understand at the time, and so I rather arbitrarily said, ‘Well Iceland probably didn’t exist at the time,’ I mean obviously it’s a big island today, and I took it out. The resulting evidence wasn’t very good, but you wouldn’t get a good fit if you’d left it in. Likewise, I kept in Rockall, which is this area here, what would otherwise be a large hole or a large gap which you can see outlined in blue here, kept that in almost for aesthetic reasons but there were sort of geological reasons which allowed you to argue that this should stay and Iceland should go. And then up here, where you have lots of overlaps, you could argue that these also were due to, like the ones in South America and Africa, due to the fact that there were a lot of igneous activity along here due to, again, hotspots, which we didn’t know about at the time. The Iceland hotspot in fact created these overlaps in a way, and Iceland would've been here at that time. And there’s a Strait here called the Davis Strait, where there’s a volcanic ridge that comes along here. But that was all plausible geologically but you did need to be a bit of a geologist to understand that. So this is the North Atlantic fit. And then the fit of both of those is shown on this map. A smaller map than the others, but you can see here at the top is the North Atlantic fit, as we’ve just discussed. And the way we’re able to make this a good fit was to close up the Bay of Biscay. Here’s Spain here, and you can see the Bay of Biscay, which would be here, today would cause a large part of Spain to overlap onto North Africa. And obviously you can see geometrically it’s much more plausible to close that up if you’re willing to close these things up, and these things up. Much more plausible to rotate Spain and make a good fit, which it is. And that is the beginnings of the fit of what we call PanGeo, which means the whole earth. It isn’t the whole earth, but now we – I haven’t got a map showing this, but over here we would have India. India would be here. We’d have Antarctica and Australia here, and all of this would be a large super continent which is known to geologists as Gondwana, whereas these northern continents, including material east of the Urals here, would be called Laurasia. But you can see there are gaps and problems which we hadn’t dealt with at the time. There’s the Caribbean area here and there’s the Mediterranean area here, and both of these areas are very complicated geologically for reasons that are related to the breakup of these continents about 200 or so millions years ago.

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