The Earth Story

Siccar Point: where modern geology started.

Located on the East coast of Scotland, this location is the most important site in the history of geology. James Hutton, widely seen as our founding father (see http://tinyurl.com/kwz2543) had a revelatory moment here in 1788 that opened his eyes to the existence of deep time, recognising in a flash of inspiration the story that these rocks had to tell us. He used this inspiration to prove his uniformitarian theory, that processes had remained the same throughout geological history and that immense cycles of time were represented by the rock record that was then being explored and discovered for the first time.

At this promontory in Berwickshire, one the site of an ancient hill fort, an angular unconformity, recording a time in geological history when no rocks were deposited because erosion was occurring, reveals some pretty astounding facts of Scottish geology. Here, near horizontal layers of 345 million year old Devonian old red sandstone overlay highly folded, near vertical, 425 Ma Silurian greywackes. At the junction, a basal conglomerate containing clasts of greywacke testifies to the erosion that preceded the deposition of the land sedimented desert sandstone. Higher up the cliff the conglomerate is absent, indicating palaeotopography, where a Devonian hill and valley sat side by side, with the hill shedding the clasts into the valley below where they eventually formed the pudding stone.

The greywackes were deposited off an ancient coastline into the Iapetus Ocean, and were once also horizontal. As this ancient sea gradually closed during the formation of the supercontinent Pangaea they were folded, thrust up and tilted to their current near vertical state. Six separate events of folding and uplifting have been discerned in the rocks. The mountain range then gradually eroded before the great Pangaean desert formed, depositing the aeolian (wind borne) desert sandstone above the already ancient and tilted rocks.

Hutton presented his findings in his books Annals of the Former World and Theory of the Earth, in which he stated "From the present state of things, we have it in our power to reason from effect to cause, and read the annals of a former earth", and while discussing his new vision of deep time "I see no vestige of a beginning (of our world), no prospect of an end". The site has now been designated a site of special scientific interest, and remains a pilgrimage for university students and geologists worldwide.

Loz

Image credit: David Souza

http://www.geopoem.com/2013/06/unconformities.html http://www.electricscotland.com/mcintyre/index_f/menu_f/geology_f/siccar_point.htm http://all-geo.org/highlyallochthonous/2011/01/the-making-of-an-angular-unconformity-huttons-unconformity-at-siccar-point/ http://www.geos.ed.ac.uk/undergraduate/field/siccarpoint/ http://www.geowalks.co.uk/isiccar.html http://www.geowalks.co.uk/isiccartours.html

Geology’s founding father: James Hutton

It is 227 years since Scottish farmer-scientist, James Hutton, published his seminal paper on the “Theory of the Earth”. Hutton was the first to introduce the idea of “deep time”. He realised that the Earth was enormously old, and that its formation and evolution can be understood in terms of processes occurring today such as volcanism, erosion and sedimentation. He published his paper as a kind of extended abstract, read out at a meeting of the Royal Society of Edinburgh. Hutton’s own words best explain his ideas:

“The purpose of this Dissertation is to form some estimate with regard to the time the globe of this Earth has existed, as a world maintaining plants and animals; to reason with respect to the changes which the Earth has undergone; and to see how far an end of termination to this system of things may be perceived, from the consideration of that which has already come to pass.

As it is not in human record, but in natural history, that we are to look for the means of ascertaining what has already been, it is here proposed to examine the appearances of the Earth, in order to be informed of operations which have been transacted in time past. It is thus that, from principles of natural philosophy, we may arrive at some knowledge of order and system in the oeconomy of this globe, and may form a rational opinion with regard to the course of nature or to events which are in time to happen.”

With this, Hutton put geology onto a scientific footing. He says that predictive models depend on careful observations and understanding current and past processes. This is exactly the scientific method that experimental Earth scientists follow today, treading the path that Hutton pioneered. Hutton began studying rocks in the hope of improving his farming, but in doing so he uncovered ideas far more significant for the wide understanding of our planet. There is a lesson here, too. Immediate societal or business problems may drive much of our scientific activity but they can miss the bigger picture. Occasionally, however, our pursuit of them may inadvertently (and fortuitously) lead to more accurate interpretations of the way the universe works, transforming our view of our environment and ourselves.

Hutton’s ideas were a radical leap from the previous faith-based views of the age and origins of the Earth, to ones based on physical evidence and reason. But he was very careful to define what could not be deduced from his evidence. Towards the end of his abstract he states, “that with respect to human observation, this world has neither a beginning nor an end”. Simply put, he had found no physical evidence for either. This is summed up more poetically in the most famous Hutton sound-bite “no vestige of a beginning, no prospect of an end”.

Hutton’s work defines the scientific method. He tested received wisdom against careful observations, when necessary building a better model based on those observations. He admitted with honesty the limits of his data.

In a future post, I will describe some of the outcrops and rocks that led Hutton to his conclusions, but in the meantime I must return to my own enquiries of the world around us. I wish you well in yours.

~SATR

Image: James Hutton (1726-1797). Detail from a portrait by Sir Henry Raeburn in the Scottish National Portrait Gallery.

Links:

www.nahste.ac.uk/isaar/GB_0237_NAHSTE_P0063.html

www.educationscotland.gov.uk/scottishenlightenment/jameshutton/

JAMES HUTTON: ‘WE FIND NO VESTIGE OF A BEGINNING, NO PROSPECT OF AN END’ James Hutton (3 June 1726 - 26 March 1797), a Scottish farmer and naturalist, is known as one of the fathers and founders of modern geology. His theories on geology came to be known as plutonism and uniformitarianism. Hutton overturned the previously held Neptunism belief system proposed by Abraham Gottlob Werner (that rocks formed from the crystallisation of minerals in the early Earth's oceans), in exchange for the Plutonian theory of decay and renewal. He lived in Edinburgh at the very time it was a bright spot in the Enlightenment, and where the intelligentsia of Europe gathered. He studied medicine and chemistry at the Universities of Edinburgh, Paris, and Leiden, in the Netherlands; then spent fourteen years running two small family farms. Hutton was the first to propose in public and with geological evidence that Earth was much older than 6000 years, which was the common believe at the time (fossils were believed to be the remains of animals that had perished during the Biblical flood). The crux of his argument for renewal came from his discovery, while investigating rocks in Scotland, that granite is an igneous rock. He found granite intruded into sedimentary rocks and saw this as evidence of subterranean fire and heat, further supported by the existence of hot springs and volcanoes. Granite was perceived at this time as a primitive (ie pre-life) rock as it contained no fossils. From his breakthrough on the formation of granite, he then realised that the core of the planet could make new rock, which in turn offset the process of erosion. Hutton realised that rocks were deposited horizontally, and therefore rocks found at non-horizontal angles must have been deposited, and then upturned. Within the unconformities between these rock layers, Hutton surmised great expanses of time must have passed. Hutton proposed an infinite age for the Earth, but in the 18th century nobody could prove the age of the Earth. The final proof of the age of the Earth did not come until the 20th century, when chemists were able to estimate the ages of rocks through rates of radioactive decay; dated to approximately 4.54 billion years old. He also proposed the Theory of Uniformitarianism: geological forces at work in the present day are the same as those that operated in the past. In other words the rates at which processes such as erosion or sedimentation occur today are similar to past rates. This was quite contrary to the belief held at the time that the Earth was formed through catastrophism: the belief that only natural catastrophes, such as the Great Flood, could account for the form and nature of a 6,000-year-old Earth. His book, An Investigation into the Principles of Knowledge, is in 3 volumes and is 2000 pages in length. Within the pages is a chapter on the origin of natural varieties – 50 years before Darwin’s On the Origin of Species were published. People mostly learned of his ideas however through his friend John Playfair, who published Illustrations of the Huttonian Theory of the Earth in 1802. Hutton was accused of being irreligious, but he was actually a deist who believed that the universe's creator had put into place a perfectly self-sustaining system. -TEL Read more about James Hutton here: http://www.james-hutton.org.uk/; http://historyofgeology.fieldofscience.com/2010/06/james-hutton-3-june-1726-26-march-1797.html http://www.todayinsci.com/H/Hutton_James/HuttonJames-Quotations.htm Photo: reproduction of a Watercolor print done by geologist James Hutton entitled: Detailed East-West Section, Northern Granite, Isle of Arran, Strathclyde. http://gallery.usgs.gov/images/07_22_2009/kOf6JVu22C_07_22_2009/large/575016-Theory_of_the_Earth.jpg