A Journey into Scotland … Part 45
A Diversion into the History of Scottish Geology Act V
The idea of continental drift goes back to 1912 and credit must go to a German geophysicist Alfred Wegener. He picked up the clues that Scottish geologists had found and noticed that they were replicated in different parts of the world. The clues were all in the fossil record. Near identical fossils found thousands of miles apart suggested two possible solutions. Either the creatures had travelled thousands of miles or the continents had. The fossils were often of animals, fish and crustaceans that lived in fresh water. A fresh water organism cannot cross a mile of salt water let alone four thousand miles of it.
Sometimes breakthroughs in science cause rejoicing and acceptance. Often they prove controversial and inspire aggressive refutation. Some scientists are good at aggressive refutation. In the case of theories that turn out to be true, the scientists who are best at aggressive refutation are not necessarily the best scientists. Everything to do with continental drift was contested. Correctly and rigorously by those keen to prove or disprove. Pig-headedly and wrongly by those whose intention was purely to rubbish the theory. Scientists claim to be governed by facts that are provable by experiments that can be repeated. If the experiments are repeated again and again with the same results then theories slowly become accepted facts. In reality good scientists follow these principles. There are plenty of people, who call themselves scientists, who appear to draw conclusions from belief and prejudice rather than an adherence to the truth.
Poor old Wegener had no means of proving his theory. He couldn’t explain how it happened and, even if he could, he had no way of measuring whether it was happening or not. North America and Europe are moving apart at a rate of less than 4 centimetres a years. I’ve had joiners and plumbers working in my house who struggle to measure 4cm accurately. Measuring the same distance from New York to Brittany was simply impossible in the pre-global positioning world of 1912.
So everything was known except whether it happened or not and how it happened. Which is a bit like saying I’ve finished building the house except for the walls, roof, floors and learning how to do it. It’s one thing to know the different elements that led up to the theory of continental drift. It’s quite another thing to piece it all together and come up with an explanation. It was natural, given the history of geology from the eighteenth century onwards, that it would be a Scotsman who solved the problem: his name was Arthur Holmes.
We like to feat our scientific heroes. We name colleges, professorships and school houses after them. Newton, Darwin and Einstein are well known names to most of us. Even those who can’t tell their evolution from their laws of motion and their awareness of gravity from their mc2 know that what they did was important. What Arthur Hughes worked out was every bit as impressive and every bit as relevant to an understanding of the world around us. It seems to me that we might be being a little selective when we hand out fame and fortune.
Arthur Holmes as a young man
It started with basic physics. There are three means of heat transfer. I know this because I was making notes in Mrs Delamere’s Physics lesson in 1970. They are conduction, convection and radiation. We were told to list examples of each for homework. I copied of Graham Holmes. He’d written down conduction: a pan on the cooker. Convection: our radiators. Radiation: the sun. I had to copy his down. We didn’t have central heating.
We were left with the impression of conduction and radiation being pretty powerful and convection being swirls of dye dancing gracefully in a beaker of water as it was warmed with a Bunsen burner. We were told that it means that heat rises and we struggled to cope with this being true given that it is always colder on top of a mountain. We lived near the Lake District; there were lots of mountains near us.
The physics is simple. If you heat a gas or a liquid it becomes less dense and rises above the more dense colder fluid. Hot always moves towards cold. Dig out that lava lamp you were given fifteen years ago and watch convection in action. The blobs of oil are heated by the lamp at the bottom and slowly rise up. At the top they cool and descend again to be replaced by fluid that is warmed in turn.
Holmes knew that beneath the earth’s crust was a huge molten layer called the mantle. Beneath that was the outer core and in the centre of the earth was the solid inner core that contained most of the heavier elements. The heat of this inner core was some 11,000 degrees Fahrenheit. (We understood Fahrenheit in 1970). The heat was caused in large part from the energy from a huge collision between the Earth and a Mars sized planet 4.4 billion years ago. That may seem like enough time for it to cool but we are talking astonishingly hot temperatures and an astonishing amount of energy*: the impact was big enough to knock enough of the Earth out into space to form the moon.
Just in case any cooling was going to take place many of the heavy elements that sank into the inner and outer core are intensely radioactive and heat producing. They ensure that there is plenty of heat. (Incidentally among all the iron, lead and nickel in the earth’s core there is enough gold and platinum to cover the earth’s surface to a depth of over a foot). On top of that (both figuratively and literally) the earth has developed a crust which has cooled enough for us to stand on, but which keeps the heat in.
Holmes knew that this gave the necessary conditions for convection on a monumental scale. A scale big enough in fact to move continents. During the Second World War he volunteered for fire watch duties. Compared with Glasgow and the Clyde, Edinburgh wasn’t heavily bombed and this gave Holmes a lot of time to work on the calculations that made him pretty sure himself that he had found the answer. The phenomenal heat from the earth’s core heats the molten rock (magma) of the Earth’s mantle setting up a convection current that rises strongly to the surface where it has nowhere to go but along the top until it has cooled sufficiently to make its way back down to the centre. In effect a conveyor belt is created and carried along this conveyor are the continents of the world. There were points where this hot stream of molten rock reached the surface and these were at the edges of the bedrock that the continents were built on. It was some time before these were more closely identified and given the name of tectonic plates.
Suddenly the mid Atlantic ridge began to make more sense. This was a place where the molten centre was forcing its way to the surface and creating new crust as it cooled in the cold waters of the Atlantic Ocean. It was a time when pieces of the jigsaw suddenly started fitting into place. You didn’t even have to go right down to the bottom of the sea to observe the process. You could actually see part of the enormous mid Atlantic ridge for yourself. It is called Iceland. Here you can actually stand on a point where Europe and America are being pulled apart. And, yes, you can actually measure the process. Professor Pall Einersson of the University of Iceland spends a good part of his working life doing just that: with the benefit of satellite GPS technology.
Holmes had provided the explanation of the near eternal destruction and renewal observed by James Hutton. (Hutton had also been proved right about his theory that the driving force behind this process was great heat from the centre of the earth). Charles Lapworth had said that an enormous sideways force had pushed up the mountains of Scotland. Holmes had provided this force. Horne and Peach had said that the fossils on different sides of the Atlantic suggested that they came from the same place. Holmes had explained this. (At least he had provided the means of explaining it). Edward Bailey had demonstrated the incalculable power of the molten rock beneath the surface and Charles Wyville Thompson had discovered the under-sea mountain range where, in the words of Professor Einarsson, “The earth’s crust is being made.”
Holmes knew that the idea wasn’t going to be universally well received and he seriously contemplated not publishing it. In his 1944 book, The Principles of Physical Geology (I have a copy of the fourth edition on my bookshelf) he leaves it until the last couple of pages before he mentions the whole convection theory. And he takes care to couch it in the language of a theory to contemplate. If this was to be how the continents were moving, then this might be how it works. The diagram he had drawn to demonstrate the process is the last one in the book.
Note the words “purely hypothetical” in the 1944 diagram
Holmes greatness and modesty go together. It took until the 1960s when the Cold War resulted in hundreds of seismic measuring stations being used, by Soviets and Americans, to monitor nuclear testing that they inadvertently also produced an accurate record of the world’s volcanic and earthquake activity. We didn’t know about it at school. The teachers didn’t know about it. For a few more years it was argued over and disputed. And then, quite suddenly it was all accepted as a truth of geological science and geo-physics. So much so that today it is taught to year 8s. I suppose it’s simple once you know how.
And much of the story of geology happened up here in north west Scotland. On a single day I cycled from Ullapool to Durness. It was further than I could ever remember cycling before in one go. As well as the best part of a hundred miles pedalling I was also travelling though 300 years of the history of geology and through 3.2 billion years of geological history.
* energy can change from the kinetic energy of the impact to other forms of energy; heat, light, gravitational potential, electrical or nuclear, etc etc but energy cannot be destroyed or created.
Footnote: Much as plate tectonics seems to be the cause of the world being a dangerous and explosive place, it is actually a stabilising phenomena. I leave the last words to Professor Sam Bowring of the Massachusetts Institute of Technology. “I think that plate tectonics is virtually inescapable on this planet. It is an exceedingly efficient way to cool the interior of the Earth.”