Portrait of James Hutton painted by Sir Henry Raeburn, dating to around 1776 (Image via Wikimedia Commons)

Scottish geologist James Hutton (1726-1797) can rightly be regarded as the father of modern geology. He made many contributions to the natural sciences, but his crowning achievement was the idea of what would come to be known as ‘uniformitarianism’.

The term ‘uniformitarianism’ (and its converse, ‘catastrophism’) was coined by the polymath William Whewell in the nineteenth century, but it was already a revolutionary concept in the eighteenth century. This was because it opened the door to the concept of ‘deep time’, that is the immensity of geologic time and the dawning realisation that Earth is of extreme age. To put the enormity of that concept in perspective, bear in mind that although it has now been established that Earth is around 4.6 billion years old, in Hutton’s time, scholarship (based mostly on the Bible) placed the age of Earth at a mere six thousand years of age.

Indeed, until the nineteenth century, there was a world-view known as ‘catastrophism’ which argued that Earth’s geological features (such as mountains) had been formed as a result of numerous sudden, short-lived catastrophic events (such as floods) which had been initiated by supernatural means and thus could be concordant with the Bible. As a consequence, fossils found in different stratigraphic layers of the Earth were seen as evidence that animals had been repeatedly wiped out in order to make way for new ones; proponents of catastrophism had no reason to think that species could change through time or that one species could evolve into another.

Hutton fiercely opposed the idea of catastrophism, and his seminal three volume Theory of the Earth, published between 1785 and 1789, argued that Earth had been shaped over extremely long periods of time by the same natural processes that operate today. These would include not only ‘large’ events such as earthquakes and volcanic eruptions, but also the everyday, more subtle erosional processes, such as rainstorms.

Simply put, Hutton argued that there was no need to invoke supernatural forces to explain the geologic record. The apparent permanency of features such as mountains and coastlines was merely a result of our short lifespans; if human beings were to live for eons, they would witness the rearrangement of the Earth’s surface – mountains would erode into plains, sediments on the sea floor would lithify (turn to stone) and new mountains would be created by uplift. Shells found in the rocks of mountain tops had not been washed there by floods (biblical or otherwise), but had been elevated from the sea-floor by the same natural processes we see today; the same processes and the same physical laws that have always operated upon the Earth.

Despite the potentially revolutionary outlook of Hutton it is only fair to note that his antiquated and tedious writing style did much to hinder the dissemination of his ideas. Indeed, so taxing was his prose style that it wasn’t until the concept was picked up by the likes of scientists such as John Playfair and Charles Lyell in the early- and mid-nineteenth century respectively, that the theory became popularised. In brief, great ideas may moulder if they are not communicated in a palatable fashion. Science matters, but so does the style in which it is presented.

Uniformitarianism facilitated a revolution in our understanding of the evolution of Earth, challenging the long-held but erroneous concept of catastrophism and in that, the prevailing view that the planet was only 6000 years old. To quote Jean Jones (1984, p.15), Hutton “..liberated geological thinking from any restrictions of timescale..”

Although Hutton established the concept of deep time for future geologists, he himself never attempted to calculate the age of the Earth because contemporary techniques were not up to the task. Wisely, he wrote:

“But, as there is not in human observation proper means for measuring the waste of land upon the globe, it is hence inferred, that we cannot estimate the duration of what we see at present, nor calculate the period at which it began..” (Hutton, 1785, p.28)

Text copyright © 2015 Victoria Ling. All rights reserved.

References

Hutton, J. (1785)  The 1785 Abstract of James Hutton’s Theory of The Earth.  Scottish Academic Press.

Jones, J. (1984)  Scottish Men of Science: James Hutton 1726-1797.  Scotland’s Cultural Heritage.

Macfarlane, R. (2009)  Mountains of the Mind: A History of Fascination.  Granta Books.

Repcheck, J. (2003)  The Man Who Found Time: James Hutton and the Discovery of the Earth’s Antiquity.  Simon and Schuster.

Photograph of Charles Lyell taken by John & Charles Watkins (Image via Wikimedia Commons)

Charles Lyell was perhaps the most famous geologist of the nineteenth century, and one of the first notable scientists to throw their intellectual weight behind Darwin’s theory of evolution by natural selection. Lyell was an eloquent and prolific writer, and one of several visionary scientists who championed the study of evolution in the nineteenth century. It was a time when many different scientific disciplines were grappling with concepts such as the antiquity of man and the idea that the Earth was much older than biblical writings had hitherto indicated. One of the great building blocks of our current understanding of the evolution of the Earth was the identification and definition of the major geological time periods, a field where Lyell played the key role.

Lesser known is that Lyell was called to the Bar (the legal profession) in 1822 and between 1825 and 1827 he was a practising barrister. However, Lyell was always more interested in geology than law, and his wealth meant that he was able to renounce the law, and so in 1828 he travelled to France and Italy to pursue geology.

When studying the Italian Tertiary strata Lyell had the idea that different stratigraphic horizons could be categorised according to the ratio of extant to extinct species of marine shells; essentially, younger strata (nearer the top of the stratigraphic column) contained a larger number of extant mollusc species, and the lower (older) units contained fewer. Using this idea, Lyell suggested that the so-called ‘Tertiary’ period should be divided into three parts – the Pliocene, Miocene and Eocene. He also re-named what had been called the ‘Primary’, ‘Secondary’ and ‘Tertiary’ eras, suggesting the names of Palaeozoic, Mesozoic and Cenozoic. These three eras have stood the test of time and of course it is no coincidence that each is separated by a mass extinction, respectively the end-Permian and end-Cretaceous events.

Geology also spearheaded the advancement of evolutionary studies in the nineteenth century, and not always in an uncontroversial manner. There is, for example, the familiar quote by the nineteenth century art critic John Ruskin which sums up the difficulty that advances in geology presented to many people in that period; the conflict between reconciling new scientific discoveries with their faith: “If only the Geologists would let me alone, I could do very well, but those dreadful Hammers! I hear the clink of them at the end of every cadence of the Bible verses.”

The first volume of Lyell’s seminal work Principles of Geology was published in 1830. In it, he explored and promoted the concept of ‘uniformitarianism’, a theory which had been earlier expounded by another Scottish geologist, James Hutton. Uniformitarianism is the name given to the idea that the Earth had been shaped over extremely long periods of time by the same natural processes that operate today (such as erosion and as we now realise plate tectonics).

Lyell stood firmly behind the concept that the geological features of Earth, such as mountains, had been formed extremely slowly and over vast spans of time. Aside from the landmark content, the most notable feature of Principles of Geology (and many of his other books) was that Lyell regarded it as an on-going piece of work – it was not published with the idea of being the ‘final say’ on the subject, but rather presented his considerations on, and analysis of, the latest research of the day. With every new edition that was published, Lyell included new evidence and revised his conclusions. Lyell modified Principles of Geology through 12 editions (the last edition was being prepared for publication at the time of Lyell’s death and was published posthumously) over nearly a 50 year period and in doing so, he made a lifelong contribution to the on-going debates regarding geological knowledge.

Some of Charles Lyell’s handwritten edits in the third edition of Antiquity of Man. (Image: Victoria Ling 2015. Book: Department of Earth Sciences, University of Cambridge)

Lyell’s hugely influential Geological Evidences for the Antiquity of Man was published in 1863. This book weaved together evidence from several scientific disciplines (mainly geology and archaeology) and a number of scientific theories that had caused controversy in preceding decades; the antiquity of man, evolution by natural selection, and evidence for previous ice ages.

What is particularly notable about this book is that although a strong supporter of evolution by natural selection, Lyell had previously distanced himself from the idea of ancient land glaciations, and this is one example where it can be argued that Lyell was not immune from the pressure of criticism from his peers. Lyell had initially been a supporter of glacial theory as proposed by the Swiss palaeontologist Louis Agassiz, and in 1840 Lyell presented a paper to the Geological Society of London forcefully supporting it. However, it sustained criticism from leading geological figures of the day and within six months Lyell withdrew the paper.

As observed by Boylan (1998), Lyell’s last words on the subject can be found in the fourth (and final) edition of Antiquity of Man where, despite stating that there is no rational alternative hypothesis to glacial theory, he then contradictorily claims: “Although I am willing, therefore, to concede that the glaciation of the Scottish mountains, at elevations exceeding 2,000 feet, may be explained by land ice, it seems difficult not to embrace the conclusion that a subsidence took place not merely of 500 or 600 feet.., but to a much greater amount, as shown by the present position of erratics and some patches of stratified drift” (Lyell 1873, p.289).

As Boylan (1998) further notes, Lyell, and one other geologist (Roderick Murchison) were the only leading geologists of this scientifically critical period of the nineteenth century – a time of huge advance in our understanding of the natural world – who went to their graves in the belief that there was no large scale terrestrial glaciation across vast areas of Europe and the Americas. It is a little ironic that Lyell – the staunch supporter of uniformitarianism and gradual change – denounced the evidence for glacial theory in favour of a ‘catastrophist’ theory of rapid sea level changes.

In the case of glacial theory, Lyell got it wrong, but in broader terms and in most other respects, he embodied the scientific method. This was reflected in his commitment to updating each new edition of his major works – always building upon and refining his research, considering new evidence with an open mind, holding his own ideas up to scrutiny and confirming or amending his previous conclusions under the weight of new evidence. And all this was transmitted in a compelling prose that caught the imagination of both scientists and the Victorian public, and today can still be read with profit and enjoyment.

Text copyright © 2015 Victoria Ling. All rights reserved.

References

Blundell, D.J. and Scott, A.C. (eds) (1998)  Lyell: The Past is the Key to the Present.  Geological Society of London.

Boylan, P.J. (1998)  Lyell and the dilemma of Quaternary glaciation.  In Lyell: The Past is the Key to the Present (D.J. Blundell and A.C. Scott, eds), pp. 145-159.  Geological Society of London.

Lyell, C. (1873)  The Antiquity of Man from Geological Evidences.  Fourth edition.  Murray.

Rudwick, M.J.S. (1998)  Lyell and the Principles of Geology.   In Lyell: The Past is the Key to the Present (D.J. Blundell and A.C. Scott, eds), pp. 1-15.  Geological Society of London.

Wilson, L.G. (1972)  Charles Lyell. The Years to 1841: The Revolution in Geology.  Yale University Press.

Adam Sedgwick aged 47. Portrait by Thomas Philips (Image: Sedgwick Museum of Earth Sciences, University of Cambridge)

Adam Sedgwick (1785-1873) was Professor of Geology at the University of Cambridge, holding the Woodwardian Chair, and was one of the most respected geologists in England in the nineteenth century. It was an era when the major geological time periods were being defined, a task in which Sedgwick played a key role with his identification of both the Devonian and Cambrian periods. It was through the definition and clarification of the major geological epochs that the immense antiquity of Earth was recognised. This realisation was critical in the development of our understanding of Earth history because prior to this period, calculations based predominantly on the Bible had led to the prevailing wisdom that Earth was only around 6000 years old. It is due to the meticulous work of scientists such as Sedgwick, that we now know it is actually around 4.6 billion years of age.

Sedgwick’s crowning glory was the identification of a period of geological time that he named the ‘Cambrian’ (from the Latin ‘Cambria’, an ancient name for Wales). This interval – which spans the period from around 543 million years ago to around 505 million years ago – is significant because it is a period where we see a remarkable ‘explosion’ in the number and diversity of fossils in the geological record.

In the early 1830s, Sedgwick teamed up with fellow geologist Roderick Murchison to map the strata of Wales. Sedgwick identified the Cambrian by relying on the physical characteristics of the rocks in northern Wales, where Murchison identified another geological period, the Silurian (named after a Celtic tribe, the Silures), by concentrating on the fossil-bearing strata in southern Wales. In 1835 they presented a paper to the British Association for the Advancement of Science on their findings entitled On the Silurian and Cambrian Systems, exhibiting the order in which the older sedimentary strata succeed each other in England and Wales. The paper founded the Palaeozoic timescale that we know today. Click here to view chronostratigraphic charts from the International Commission on Stratigraphy (ICS).

However, controversy arose because Sedgwick and Murchison could not agree on where the boundaries between the Cambrian and Silurian lay. The crux of the problem was that Murchison had misinterpreted the age of certain rocks in several areas in the Welsh borders. This led him to claim that the rocks forming the baseline of his system belonged to the Lower Silurian, whereas Sedgwick argued that they should be placed in the upper part of the Cambrian system.

The dispute was eventually resolved by another geologist, Charles Lapworth (1872), who introduced an intermediate period (the Ordovician, named after another ancient tribe, the Ordovices) separating the Cambrian and the Silurian, and equivalent to the disputed “upper Cambrian-lower Silurian” beds. Each of these periods is now known to be characterized by distinct fossil assemblages and remain standard in geology. Sadly the acrimonious nature of this disagreement culminated in the Geological Society of London, of which Murchison was President, and Sedgwick was a past-president, refusing to publish any of Sedgwick’s papers on the subject.

Sedgwick also mentored a young Charles Darwin, who at the time was a fledgling naturalist reading theology at Christ’s College, Cambridge. Darwin accompanied Sedgwick on fieldwork to Wales and attended his lectures. Darwin’s endorsement by his mentors, primarily John Henslow but also Sedgwick, was instrumental in gaining Darwin a position on the famous voyage of HMS Beagle, which in turn was key to developing Darwin’s thoughts behind the groundbreaking On The Origin of Species. However, Darwin’s book had enormous theological implications and Sedgwick was notably anti-evolutionary in his thinking. He was a devout Christian and believed that acceptance of the idea of evolution would cause a breakdown in the moral fabric of society. After all, he would have no doubt reasoned, if we are simply descendants of monkeys what warrant do we have for our ethics? In a famous letter written to Darwin shortly after he received a copy of the first edition of On The Origin of Species, Sedgwick set out those fears as well as his appreciation for Darwin’s great work. Despite Sedgwick’s outspoken opposition to Darwin’s theory of evolution by natural selection, it is testimony to the open-mindedness of both men that they remained on good terms throughout Darwin’s lifetime.

Darwin clearly enjoyed Sedgwick’s mentorship and it is easy to understand why. Sedgwick was a charismatic speaker and his lectures were always well attended despite not being compulsory for students at that time. He gave a course in Cambridge which ran nearly every year from 1819 to 1870, by which time he was 85 years of age. As Colin Speakman (1982, p.88) notes, Sedgwick’s inspirational persona is summed up by a statement made in one of his lectures:

“I cannot promise to teach you all geology, I can only fire your imaginations.”

Most scientists are inspired by their own research, but the ability to capture that excitement and inspire scientific curiosity in others is a much rarer gift.

The Sedgwick Museum. Part of the Department of Earth Sciences, University of Cambridge (Image: Victoria Ling 2015)

Sedgwick also stressed the importance of fossils as a means of determining relative age and was the first Cambridge scholar to earnestly begin collecting fossils for the University’s geological collection. Many of these specimens were acquired from other collectors, including a number from the pioneer fossil collector Mary Anning. The fossils that Sedgwick amassed built upon a collection of around 10,000 specimens which were bequeathed to the University of Cambridge in the will of John Woodward, which was recognized in the early eighteenth century as one of the most significant collections in the world. These are still housed in the Sedgwick Museum, a building that arose as the result of a wildly successful subscription after Sedgwick’s death, and forms part of the Department of Earth Sciences in the University of Cambridge.

Text copyright © 2015 Victoria Ling. All rights reserved.

References

Lapworth, C. (1872)  On the tripartite classification of the Lower Palaezoic rocks.  Geological Magazine 6, 1-15.

Levin, H. (2010)  The Earth Through Time.  Wiley.

Rupke, N.A. (1983)  The Great Chain of History. William Buckland and the English School of Geology (1814-1849).  Clarendon.

Sedgwick, A. and Murchison, R.I. (1835)  On the Silurian and Cambrian Systems, exhibiting the order in which the older sedimentary strata succeed each other in England and Wales. British Association for the Advancement of Science Report, 5th Meeting, 59-61.

Speakman, C. (1982)  Adam Sedgwick: Geologist and Dalesman 1785-1873.  Broad Oak Press, The Geological Society of London, and Trinity College, Cambridge.