Scotland’s Time Lords Prof Stuart K Monro, Scientific Director, Our Dynamic Earth and Honorary Professor, University of Edinburgh Prologue This article is an opportunity to reflect on how Earth science was born in the City of Edinburgh and how ideas about Earth processes have changed up to the present day. There have also been some dramatic changes in our attitudes to public engagement with science in the 21st century. As a geologist, I frequently quote the phrase “geologists are good company, especially for other geologists” which reflects the unfortunate attitude of some specialists in a variety of professions to engage more with each other than with the wider community. I contrast that with the nature of Society during the Edinburgh Enlightenment when individuals with widely different interests came together in discussion, often over a jug of claret, thus fostering the development of the polymath. It was in this climate that the modern understanding of geology, the science of the Earth, was born, here in Edinburgh over 200 years ago. Here is where our story, represented in the first gallery of Dynamic Earth, begins… James Hutton, medic, chemist, farmer and the Father of Modern Geology James Hutton was born in Edinburgh on the 3rd June 1726, the son of the City Treasurer. At the age of 17, he was apprenticed to a lawyer; but this was not a successful move. According to his biographer John Playfair,“… happily the force of genius cannot always be controlled by the plans of a narrow and short-sighted prudence. The young man…was often found amusing himself and his fellow apprentices with chemical experiments instead of copying papers”. With an interest in chemistry, it was medicine that he studied when he attended the University of Edinburgh. In those days, chemistry was an integral part of a medical education though few students actually matriculated for a degree programme, preferring instead to attend individual lectures. Three years later he continued his studies in Paris pursuing “…with great ardour the studies of chemistry and anatomy” and took the degree of doctor of medicine in 1749 at Leyden. His thesis was on the circulation of blood. His departure to the continent to complete his studies was a common enough occurrence then, however it may have been precipitated by having had a son during his early twenties by a Miss Edington! In 1750 he returned to Edinburgh and resumed chemical experiments with his friend James Davie. Their work on the production of sal ammoniac – ammonium chloride, a salt used in dyeing and working with brass and tin – led to a profitable partnership. Hutton also had a keen interest in agriculture and farmed at Slighhouses and Nether Monynut in Berwickshire, farms he had inherited from his father. Hutton wished to apply his scientific understanding to agricultural practice and travelled extensively to gain new ideas, introducing the Suffolk plough to Scotland. It was undoubtedly these travels that fostered his interest in the processes that shape the natural world. He visited Arran and Jedburgh and discovered the geological relationship, the uncomformity, in both places where horizontal or gently dipping rocks rest on top of more steeply dipping rocks. More importantly, he recognised the story that these exposures were telling. In Berwickshire he had seen the steeply dipping rocks that make up the Southern Uplands and also the more gently dipping rocks around Dunbar. He surmised that somewhere on the Berwickshire coast, these two rock formations would come together. Thus, with two friends, Sir James Hall and John Playfair, he sailed from Dunglass, southwards along the coast to discover Siccar Point and its dramatic unconformity. Here Hutton revealed to Hall and Playfair the true significance of what they were seeing. Hutton recognized that the vertical rocks would have been initially laid down horizontally then subsequently squeezed into a vertical position forming large-scale folds and building mountains. Before the second, gently dipping rocks are laid down; there would need to be a long period of erosion, removing the mountain. Finally the second set of rocks would be laid down. The unconformity between the two sets represents, therefore, a period of time when mountains were raised and then eroded away. These observations should be seen in the context of the establish wisdom of the time, that of Archbishop Ussher of Armagh who pronounced that the world was formed on the evening prior to the 23rd of October 4004BC. Hutton demonstrated to his friends at Siccar Point that the Earth had to be very much older and thus started a quest for the age of the Earth which continued through to the 1940s when Arthur Holmes produced a revised age akin to that accepted today. Hutton’s other great controversial idea was that some rocks had been molten and injected into sediments. He was a Plutonist. In this he was at odds with Robert Jameson, the Neptunist, who believed that these rocks were formed by precipitation from some primeval ocean. The evidence for Hutton’s view can be clearly seen at what is now called “Hutton’s Section” at the foot of Salisbury Craigs. The relationship between the Craigs rocks and the underlying sediments indicates that the sediments have been forced up and broken off by forceful emplacement of what must have been molten rock. Charles Lyell, the great communicator Hutton’s ideas were the subject of two lectures given to the newly-formed Royal Society of Edinburgh on 7 March 1785 and 4 April 1785. However, he did not publish his Theory of the Earth in book form until 1794. Unfortunately the book was so badly written that few succeeded in reading it. In 1802, five years after Hutton’s death, John Playfair tried to explain Hutton’s theories in his Illustrations of the Huttonian Theory of the Earth. However Hutton’s concepts were not widely recognised until Sir Charles Lyell included them in his Principles of Geology in 1833. Charles Lyell was born in Kinnordy, Forfarshire (now Angus) and was the great communicator of Hutton’s geological ideas and concepts. His Principles of Geology brought Hutton’s ideas forward. Importantly, Charles Darwin had a copy of Lyell’s book with him on his voyage on the Beagle. It was a book which greatly influenced Darwin’s thinking, giving him a framework of deep time in which evolution by natural selection could work. Lyell went on to be one of the foremost geologists of his time and held the post of Professor of Geology at King's College London in the 1830s. He was a great advocate of uniformitarianism, a concept that related back to Hutton’s thinking that the earth was shaped entirely by slow-moving forces still in operation today, acting over a very long period of time. The other side of the coin was that of catastrophism, where the Earth has been affected in the past by sudden, short-lived, violent events, possibly worldwide in scope. Now of course, it is recognized that both processes are operative; slow-moving change in many areas but violent and catastrophic events like volcanic eruptions, earthquakes and tsunami in others. The scientific understanding of our Earth continues to evolve. The “Readers of the Rocks”, Ben Peach and John Horne Fundamental to Hutton’s ideas was the concept that rocks would be put into a vertical disposition by major compressive forces, building mountains. Though Hutton surmised this process, he was unaware of the mechanism by which it could be achieved. During the 19th century prominent geologists conducted a prolonged and bitter debate, the Highland Controversy, about the geological relationships exposed in the north-west Highlands of Scotland. The protagonists were, on the one hand Roderick Murchison and Archibald Geikie and on the other, James Nicol and Charles Lapworth. This was finally resolved in 1907 by the work of mapping geologists from the Geological Survey, Ben Peach and John Horne. The main issue was that the Moine schists at the top of the crag appeared to be older than the Cambrian and Ordovician rocks lower down. Murchison and Geikie believed the sequence was wrong and that the Moine schists must be the younger rocks. The conundrum was explained by Peach and Horne to be due to the action of a low- angle thrust fault bringing older rocks from the east over the top of the younger rocks. This was evidence of the major compressive forces envisaged by Hutton. Subsequently investigations in areas where there are much younger mountain chains such as the Alps and the Himalayas have confirmed that major compressive forces can build mountains by generating large-scale overfolds called nappes and the stacked, thrust slices which Peach and Horne recognized in the north-west Highlands of Scotland. However, what was yet unknown, was the mechanism by which these major compressive forces could be generated. That was all to change in this evolving story. The Second Time Lord, Arthur Holmes Working in Durham and then in Edinburgh, Arthur Holmes was able to use the emerging science of radioactive decay to date rocks and establish a numerical timescale for the events that shaped the Earth. His interest in geochronology dates back to his undergraduate experience where he dated a Devonian rock from Norway as 370my. For the first time, rocks and the events associated with their formation could be accurately dated and a chronological story of the evolution of the Earth could be started to be written. Holmes was undoubtedly the other historical character who could stand alongside Hutton as a “Time Lord”. Global impact of these innovators There is an international dimension to this story which starts with a German polar explorer and meteorologist, Alfred Wegener who, in 1912, considered that the geometrical fit between South America and Africa suggested that they had been at one time joined and through time had drifted apart; the theory of continental drift.