What is 'Deep Time' in geology? (Hutton's Unconformity)

Hello friend! Deep Time is a fascinating concept. I'm happy you're here to learn more about it. This following text is taken out of my free online program MENTOR EARTH. It truly is free, no hidden costs and no upselling. Just a unique program about planet Earth and philosophy. Have a look if you're down for it! :)

Experience the hypnotizing effect of deep time and accompany James Hutton on his ground-breaking journey to Siccar Point. – Daniela


It is one of the greatest contributions geology has made to society and the sciences: deep time.

What is deep time?

Deep Time describes the enormous amount of time of Earth’s history, the vast time scale of geological events and processes, that humans can’t conceive.

Our own plans, our imagination, does not go beyond a couple of years or decades. Our lifetime is about 100 years. Nobody is able to entirely comprehend these timespans of Earth and the universe. We can barely comprehend what “the next 20 years” means. What's the difference between 10,000 and 1,000,000 years in your head? In mine, there is almost no difference! These numbers, these ages, are equally unfathomable.

James Hutton's Unconformity

The term "deep time" was coined by the American writer John McPhee in this book “Basin and Range” in 1981. But the concept, the notion of deep time, was first grasped by the Scottish physician, agriculturalist, philosopher, and geologist James Hutton in the 18th century. He was an outstanding thinker and observer of the natural world.

James Hutton, public domain

Hutton believed that the surface of the Earth is formed by consistent natural processes such as erosion, deposition in the sea and consolidation, folding and uplifting of rocks, that Earth is a system with cooperating powers that drive this system, and that processes of the past work similar to those today. He knew that geological processes took enormous lengths of time. In fact, he thought those processes took “a time which is indefinite” – a revolutionary thought in a world that still believed the Earth is only 6,000 years old. He proposed these ideas and his paper Theory of the Earth in front of the Royal Society of Edinburgh in 1785.

In 1788 James Hutton went on a boat trip with his friends John Playfair and Sir James Hall of Dunglass with the specific intention to find proof for his hypothesis that he had presented in front of the Royal Society of Edinburgh three years prior. He knew he had to look for horizontal rocks beneath vertical rocks.

Location of Siccar Point (Hutton's Unconformity) southeast of Dunbar in Scotland


Eventually, they came across a small, rocky promontory which is located on the eastern coast of Scotland, just southeast of Dunbar. This small, rocky patch would later become world-famous as the striking angular unconformity at Siccar Point, also called Hutton’s Unconformity. This unconformity would change the course of geology forever.

What is a geological unconformity?

An unconformity is a geological feature that marks the disruption of the chronological continuity of a rock sequence or rock record. In other words: It is a place where a layer of rock is missing, which equals a break in time in a rock record, which simply means that time is missing.

The geology at Siccar Point

At Siccar Point, almost vertical, dark-colored rocks stick out beneath slightly tilted red-orangecolored rocks, clearly forming an angle. James Hutton writes in his “Theory of the Earth”:

“At Siccar Point, we found a beautiful picture of this junction washed bare by the sea”.


Siccar Point photographed by Dave Souza

Absolute dating methods were not invented yet, and Earth’s eras and periods and epochs were not yet defined either. So what James Hutton didn’t know at the time, but what we know today, is that these vertical rocks are 430-Ma-old schists that were deposited in the deep, ancient Iapetus Ocean as greywackes, a particular type of sandstone, and as mudstones in the Silurian Period. They are overlain by almost horizontal, but gently tilted, rock layers out of red sandstone from the Old Red Continent, that were deposited there by river systems, so on land, in the Devonian Period, so 370 Ma ago. And this gap in the rock record, those rocks that are not there, those 60 million years that are not there, is the unconformity. Rock is missing, time is missing.

Geology of Siccar Point (Hutton's Unconformity). Photograph by David Souza

This is striking due to several reasons:

1. Almost all sediments in the entire Earth are deposited horizontally. This automatically means that the vertical rocks in the basement were folded and uplifted after they were deposited and consolidated, so after they formed into rocks.

2. There had to be a time when either no sediment was deposited, or erosion of land surface took place. Otherwise there would be no gap in the rock record.

The bottom layers from the Silurian were deposited deep in the ancient Iapetus Ocean and folded when this ocean was closed as three ancient continents collided to form a bigger equator-straddling continent called Laurussia or Old Red Continent, as well as the equatorstraddling Caledonian Mountains.

The red sandstone layers were deposited later, about 60 million years after the bottom layers were folded and eroded. The top layer consists of eroded material from the previously formed Caledonian Mountains from the Old Red Continent. The red rocks, the red sandstones, were deposited in the Devonian Period, and during that time 400-370 Ma ago, Scotland was located between the equator and 30 °S (degrees latitude south). This is the same latitude where today deserts such as the Namib Desert and Atacama Desert as well as the Australian Outback are located. So in prehistoric Scotland, that was part of the Old Red Continent, the climate was hot, dry and desert-like as well. This dry climate is responsible for the red color of the overlying rock layers.

Hutton realized this and deduced from his prior yearlong diligent observations and interpretations of nature that these processes could not happen in only 6,000 years. These processes, the deposition, the solidification, the lithification of rock, the folding and the uplift, the elevation, and the erosion could not happen in only 6,000 years. Earth must be older, as these geological processes take enormous lengths of time.

He used his observation at Siccar Point and at other locations as proof for his theory of uniformitarianism. This is a fundamental geological assumption that allows geoscientists to explain the modern geological processes as the consequence of ongoing, continuous natural processes. Uniformitarianism says that processes in earlier times work exactly the same way as they do today. In other words: James Hutton saw proof in Siccar Point that the Earth and the landscapes are formed and shaped by uniform processes such as sedimentation, uplift, and erosion. And with that he was the first to describe the rock cycle and the first to realize that rocks are recycled.

John Playfair, who accompanied James Hutton, later recounted this special day, and wrote:

“Dr Hutton was highly pleased with appearances that set in so clear a light the different formations, and where all the circumstances were combined that could render the observation satisfactory and precise … We felt necessarily carried back to a time when the schistus on which we stood was yet at the bottom of the sea, and when the sandstone before us was only beginning to be deposited, in the shape of sand or mud, from the waters of the supercontinent ocean… The mind seemed to grow giddy by looking so far back into the abyss of time; and whilst we listened with earnestness and admiration to the philosopher who was now unfolding to us the order and series of these wonderful events, we became sensible how much further reason may sometimes go than imagination may venture to follow.”


This beautiful anecdote shows us that on this particular day in eastern Scotland in 1788, deep time was not only observed, but viscerally felt by these men. John Playfair calls Hutton a philosopher, which proves to me that geology and philosophy are intrinsically connected.

The discovery of Siccar Point had profound influence on the development of modern geology. James Hutton made other key observations about the workings of Earth and is therefore known as the Founder of Modern Geology. And Siccar Point is internationally known as the Birthplace of the Geological Sciences.


What can deep time teach us about life?

Deep time contains all the time it took to form the universe, the planets, and the evolution of life. It contains the story of the planet you live on. It’s the story of your home. Of humanity’s cradle. It’s a wonderful, awe-inspiring story, isn’t it?

To me, the most magnificent realization is that the past is not “another world”. It has always been the same “world”, the same planet, the same Earth, simply dressed in other clothes.

Deep time reminds us of our mortality. It honors the past, and the future. With that in mind, is living in the present moment, which has become so popular in modern culture, enough?

Deep time encourages long-term thinking. Living in the present doesn’t. Long-term thinking is necessary to consider long-term effects, consequences, of behaviour in the future, and to honor and be appreciative of what has been there before. It’s an inclusive, broad, all-encompassing way of thinking, instead of a narcissistic, self-centered one.

Deep time, time-awareness, makes us reevaluate what we want to do with our limited time on Earth, who we want to spend our time with and what we want to prioritize and do. Time is not our worst enemy, but our best friend. With the passage of time, things develop, evolve and mature. Time has the power to make us become more selective and disciplined and caring, as we realize time is limited. We don’t have forever. We should use that time wisely.

Here are some thought prompts:

  • What does the concept of deep time evoke in you?
  • Can you see how an awareness of time enriches your life?
  • The next time you see a rock formation, can you see beyond its present state and visualize its past and its future? Can you see the full picture? Can you try?
  • The next time you see a person, can you see beyond their present state and understand they have a history you don’t know about?
  • The next time you look in the mirror, can you see a person who has lived and made experiences, who has a past, who has a family tree, who is part of a system, part of evolution?
  • Do these insights change your way of seeing and perceiving the world? How would this change your values, thoughts, feelings and actions?
  • Does this knowledge change the way you treat Earth, others and yourself?


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About the author

Daniela is convinced that gaining deep insights into planet Earth and travel destinations creates meaningful, grounding and memorable life + travel experiences. She explains fundamental geological processes that form and shape landscapes and combines these insights with philosophical and philanthropical views in her online courses, articles, and newsletter. She currently studies for a master's degree in geosciences at the University of Cologne. She is the owner and founder of EarthyMe, EarthyUniversity and the Science of Travel blog and the STORIES OF EARTH newsletter.




Headline image: Pexels.com

Portrait of James Hutton: Henry Raeburn, Public domain, via Wikimedia Commons

Map: Google Earth

Photograph of Siccar Point: Dave Souza, CC BY-SA 4.0, via Wikimedia Commons. Annotations made by author of this article. 


Please find all the sources listed in a spreadsheet that is available for download in my program MENTOR EARTH

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