Richard Fortey on Deep Time
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Richard Fortey has devoted his long and prolific research career at the Natural History Museum in London to the study of fossils, especially the long-extinct marine arthropods called trilobites. In an earlier episode of Geology Bites, he talked about measuring time with trilobites. In this episode, he describes how it was the fossils in the geological record that gave us the first markers along the runway of deep time, providing the structure and language within which our modern conception of deep time emerged.
Photo: Eamonn McCabe/The Guardian
Podcast Illustrations
The modern geological timescale (December 2024 version). Many of the names we have given to the various periods were derived from locations where the rocks of that age were first studied. The temporal boundaries of the periods were usually defined by the first appearance of certain fossils in sedimentary rocks. With the advent of radiometric dating of minerals, especially in igneous rocks adjacent to or intercalated with fossil-bearing sedimentary rocks, absolute ages have been assigned to boundaries between the periods.
International Commission on Stratigraphy
Bishop Usher (1591-1656) calculated the date of Creation to have been nightfall on 22 October, 4004 BC. He determined this from a literal reading of the Old Testament. Right: title page of Usher’s Annals of the World
Painting by Sir Peter Lely
Count Buffon (1707-1788) calculated the age of the Earth by estimating its rate of cooling. He experimented with a small globe having a composition resembling that of the Earth. This led him to estimate that the Earth was at least 75,000 years old. One key reason his figure was much lower than the actual age was the omission of radioactive heating of the Earth by the decay of isotopes, particularly those of potassium, uranium, and thorium.
Painting by François-Hubert Drouais
The major angular unconformity at Siccar Point on the east coast of Scotland. Here the more gently sloping Devonian sandstones (c.375 Ma) overlay the near vertical Silurian greywackes (c.440 Ma). Viewed by James Hutton while on a boat trip in 1788, this was one of the sites that solidified Hutton and Lyell's new concepts of Earth's geology: that it was formed by slow continuous processes similar to those still occurring today operating over vast periods of time.
Photo: Rob Strachan
Portrait of James Hutton, often referred to as the “Father of Modern Geology.” Here is the final paragraph of this 1788 paper Theory of the Earth.
WE have now got to the end of our reasoning; we have no data further to conclude immediately from that which actually is: But we have got enough; we have the satisfaction to find, that in nature there is wisdom, system, and consistency. For having, in the natural history of this earth, seen a succession of worlds, we may from this conclude that there is a system in nature; in like manner as, from seeing revolutions of the planets, it is concluded, that there is a system by which they are intended to continue those revolutions. But if the succession of worlds is established in the system of nature, it is in vain to look for any thing higher in the origin of the earth. The result, therefore, of our present enquiry is, that we find no vestige of a beginning,--no prospect of an end.
Hutton, J. (1788), Transactions of the Royal Society of Edinburgh, vol. I, Part II, 209
Painting by Sir Henry Raeburn
Portrait of Charles Lyell, a contemporary of James Hutton, who, in his multi-volume Principles of Geology, proposed that the Earth was shaped entirely by slow-moving forces still in operation today, acting over a very long period of time. This view was termed uniformitarianism, as opposed to catastrophism, which posited that the Earth was largely shaped by sudden, short-lived, violent events.
Painting by Alexander Craig
The first geological map of Britain, created by William Smith in 1815. In the podcast, Fortey explains that Smith used fossils as markers of the different geological units, without necessarily believing in the theory of evolution.
Clock of the Long Now
Prototype of the Clock of the Long Now. It was activated on December 31, 1999, and is on display at the Science Museum, London. The clock is intended to keep time for 10,000 years. The final version of the clock is intended to be an enormously enlarged version of this prototype — a vast mechanism big enough for visitors to walk through and installed near a National Park in Nevada in a chamber hollowed out of a limestone cliff.
The clock uses a torsional pendulum that rotates slowly, making the clock tick once every 30 seconds. This prototype is driven by falling weights (right), but the full-size clock would be powered by the energy from footfalls of visitors or by changes in temperature. Any drift in the clock’s rate will be corrected by a mechanism sensing the sun passing overhead at noon.
Further Reading
Fortey. R. A. (2011), Charles Lyell and Deep Time, Geoscientist October 9, 2011, the Geological Society
Fortey, R. A. (1999), Life: A Natural History of the First Four Billion Years of Life on Earth, Knopf Doubleday
Fortey, R.A. (2010), Trilobite, Knopf Doubleday