Abstract Four of the Geological Society’s 13 founders were medical men: William Babington, James Parkinson, James Franck and James Laird, the Society’s first Secretary. All were physicians and mineralogists except Parkinson, an apothecary surgeon and fossilist. At least 20 percent of the Society’s early members were also medical practitioners whose prime interest was mineralogy. The subject was taught as part of medical training, required as it was in the fabrication of medicines, thus medical men were drawn into mineralogy and on into geology. In 1805 a number of medical practitioners broke away from the constraints of their parent body, the Medical Society of London, to form the Medical and Chirurgical Society, which became a role model for the young Geological Society when challenged by its parent body, the Royal Society. Driven by wealthy mineral collectors and patrons of science like Charles Greville, one reason – perhaps the reason – for founding the Society was to map the mineralogical history of Britain. Towards this endeavour, Babington’s expertise in mineralogy brought people together, Laird organized them and Parkinson was invited because he was not a mineralogist. Franck was unable to participate significantly, being away at war for much of the time. The contribution made to the founding of the Geological Society by each of the medical founders is examined, and a biographical sketch of each man reveals the close relationship between medicine and the emergence of this new science of geology.

Abstract John Stuart, the third earl of Bute and the British Prime Minister from 1762 to 1763, and the apothecary surgeon James Parkinson both amassed large and important geological collections; both believed in the biblical Deluge; both admired the work of Jean André de Luc; and both were fascinated by the study of geology. Each sought a theory that would explain the geological phenomena they observed but which also allowed them to maintain their religious integrity. They were men of their time, struggling to come to terms with a new science that challenged their strongly held religious beliefs. Bute's Observations on the Natural History of the Earth , never published, provides us with a snapshot of his thinking about prevailing theories of the Earth. He dismissed all except those that fitted the geological facts as understood at the time, but was nevertheless unable to progress from a rigid belief in the biblical Flood having been a miracle. Parkinson's Organic Remains of a Former World reveals a man fully conversant with contemporary geological ideas being propounded elsewhere in Europe. Also highly religious, Parkinson oscillated between his deeply held beliefs and the contradictory evidence provided by the fossils he held in his hand.

Abstract Only ten years after the discovery of radium in 1897, Arthur Holmes (1890-1965) began his studies at the Royal College of Science in London where he completed the very first U/Pb age determination designed specifically for that purpose. His continued interest in radioactivity and its effect on the thermal history of the Earth led to his early recognition that the age of the Earth should be measured in thousands, not hundreds, of millions of years, a subject he pursued for the rest of his career, despite considerable opposition from traditional geologists. Following a short period in Burma, he returned in 1922 to find that not only had attitudes to the age of the Earth changed, but that geologists were embroiled in a new controversy over continental drift. Evidence is put forward that suggests Holmes may have been aware of Wegener's theories virtually from the time they were proposed, and that by 1924 he was already searching for his own theory which would explain all geological processes. His profound understanding of the effects of radioactivity on the internal processes of the Earth, and his advanced knowledge of petrology, placed him in a unique position to develop a mechanism for driving continental plates around the globe. The progression of his ideas for this mechanism - convection currents in the mantle - and the unifying theory that that led to, is traced through his papers and letters to colleagues.

Abstract The age of the Earth has been a subject of intellectual interest for many centuries, even millennia. Of the early estimates, Archbishop Ussher’s famous calculation of 4004 bc for the date of Creation represents one of the shortest time periods ever assigned to the Earth’s age, but by the seventeenth century many naturalists were sceptical of such chronologies. In the eighteenth century it was Nature that provided the record for Hutton and others. But not all observers of geology enquired about time. Many, like William Smith, simply earned a living from their practical knowledge of it, although his nephew, John Phillips, was one of the first geologists to attempt a numerical age for the Earth from the depositional rates of sediments. For more than fifty years variations of that method prevailed as geology’s main tool for dating the Earth, while the physicists constrained requirements for a long timescale with ever more rigorous, and declining, estimates of a cooling Sun and Earth. In 1896 the advent of radioactivity provided the means by which the Earth’s age would at last be accurately documented, although it took another sixty years. Since that time ever more sophisticated chronological techniques have contributed to a search for the oldest rocks, the start of life, and human evolution. In the attempt to identify those landmarks, and others, we have greatly progressed our understanding about the processes that shape our planet and the Universe, although in doing so we discover that the now-accepted age of the Earth is but a ‘geochemical accident’ which remains a contentious issue.

Abstract Arthur Holmes (1890–1965) was a British geoscientist who devoted much of his academic life to trying to further the understanding of geology by developing a radiometric timescale. From an early age he held in his mind a clear vision of how such a timescale would correlate and unify all geological events and processes. He pioneered the uranium–lead dating technique before the discovery of isotopes; he developed the principle of ‘initial ratios’ thirty years before it became recognized as the key to petrogenesis, and he wrote the most widely read and influential geology book of the twentieth century. But despite all this, much of his contribution to geology has gone unrecognized in the historical literature. This paper attempts to redress this omission, to dispel some of the myths about Holmes’ life, and to trace his contribution to the development of the geological timescale.

Abstract In North America, prior to the Second World War, discussions on the age of the Earth were a minuscule part of the geological literature, as demonstrated by the small number of papers indexed to the subject in bibliographies. Indeed, during the first quarter of the twentieth century, there were few general papers on this topic circulating among those geologists who dealt with sedimentary rocks and fossils; nevertheless, evidence is provided that many geologists were aware of the ‘debate’ going on in Britain. As the methodology for determining the length of geological time dramatically changed during the four decades represented here, so too did the evolution of ideas about the age of the Earth. These can conveniently be divided into three time periods: before, during and after the discovery that radioactivity could be applied to the dating of rocks. The first section reviews the attitudes of geologists in America to the age of the Earth in the 1890s. It is followed by their reactions to the discovery of radioactivity. The third part discusses two major publications on the age of the Earth which reflect the ultimate acceptance, by geologists, of the long timescale revealed by radioactivity. Because much of the early work on radioactivity was being done in Europe, American geologists were marginally later than their British counterparts in accepting the concept of radiometric dating, but by the end of the period under consideration they led the field in geochronology.