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Historical geology

Textbook: Prentice Hall Earth Science, Tarbuck & Lutgens. Chapter 12: Geologic time

Modern geology starts with Georges-Louis Leclerc

Also known as the Comte de Buffon (1707-1788). Compte is a title of French noblity. The equivalent English term is ‘Count’ or ‘Earl’.  Having this title does not mean that one is actually part of a royal family; the title could be purchased by an individual with both enough money and high social standing. Buffon is a small town in eastern France.

We’ll learn about Leclerc with this excerpt from ‘Understanding Evolution’, from the University of California Museum of Paleontology: http://evolution.berkeley.edu/evolibrary/article/0_0_0/history_06

In the 1600s most naturalists believed the world was a few thousand years old and that species were created separately and organized into an unchanging hierarchy, with humans positioned just below the angels.

In the 1800s, Darwin described a world that was inconceivably old, one in which life gradually changed from one form to another without any need for direct supernatural intervention.

Roughly midway between those two views—both chronologically and intellectually—was the remarkable Georges-Louis Leclerc Buffon.

François-Hubert Drouais (1727-1775), Portrait de Georges-Louis Leclerc, comte de Buffon, Localisation : Musée Buffon à Montbard.

François-Hubert Drouais (1727-1775), Portrait de Georges-Louis Leclerc, comte de Buffon, Localisation : Musée Buffon à Montbard.


Buffon’s career centered on a single enormous project: an encyclopedia he called Histoire Naturelle, which he planned to contain everything known in his day about the natural world. (Buffon managed to publish 36 out of his projected 50 volumes before he died.)

611 GEORGES LOUIS LECLERC DE BUFFON Oevres. 31 Bde. 1774 http://www.kettererkunst.com/result.php

Oevres. 31 Bde. 1774

To create it, he was able to draw on his own astonishing expertise, which ranged from astronomy to botany, as well as the knowledge of experts he consulted. But in writing his encyclopedia he did not merely parrot the opinions of others. Instead, he tried to explain all of the facts he amassed with overarching theories about the planet and its inhabitants.

Buffon realized that to interpret the world, he had to understand its history. And despite censures from the Church, he did not rely on the Bible as a strict guide to that history. Instead, he used the new physics of Isaac Newton to conjecture how matter in motion might have formed the Earth.

Buffon proposed that a comet striking the sun had broken off debris that became the planets of the solar system. Initially, the Earth was scorching, but gradually it cooled until molten rock turned to dry land and clouds rained down to form oceans. Buffon estimated the entire process took over 70,000 years. To most Europeans of Buffon’s time, who considered the Earth to be fewer than 7,000 years old, this was practically an eternity. {The details we now know to be incorrect – but the scientific, rather than religious, hypothesis, was what set him apart from his peers. – RK}

Buffon argued that life, just like Earth, had a history. Like many other Enlightenment thinkers, he thought that it could be generated spontaneously under the right conditions. In the hot oceans of the early Earth, Buffon claimed that vast amounts of life were generated from unorganized matter—even large animals sprang into existence. In time, as the world’s climate cooled, many animals migrated to the tropics. Their migration made sense of the discoveries in Buffon’s day of fossil elephants in Siberia and North America, while living elephants were only found in Africa and South Asia (see figure, right). The Siberian species gave rise to today’s elephants, while the North American forms simply became extinct.

…Buffon’s theories were visionary yet doomed, because they were based on the relatively skimpy evidence that eighteenth-century naturalists had at their disposal.
* his estimate of the Earth’s age turned out to be far too young
* his notions of biological change were not based on a coherent mechanism.

Yet his theories foreshadowed some of the most important developments in the natural sciences in the decades that followed his death—from Cuvier’s discoveries about extinctions, to the evidence that Lyell and other geologists found for a vast age of the planet and life itself, to Darwin’s own theory of evolution.

It may be true that no single idea of Buffon’s has withstood the test of time. But his work was still a milestone of science because he thought about the Earth and life in ways that few had before—both life and the Earth had a history.

— The above text comes from the UE (Understanding Evolution), a collaborative project of the University of California Museum of Paleontology (UCMP) and the National Center for Science Education. Credits for the authors are here — http://evolution.berkeley.edu/evolibrary/credits.php


1794 – James Hutton, Founder of Modern Geology

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James Hutton 1726-1797.  Scottish geologist, physician, naturalist – originated the theory of uniformitarianism. He explained the features of the Earth’s crust by means of natural processes over geologic time.

James Hutton is the father of modern geology. His most famous work “An Investigation of the Principles of Knowledge and of the Progress of Reason” – 1794

“James Hutton: The Founder of Modern Geology” Donald B. McIntyre and Alan McKirdy

“The Man Who Found Time: James Hutton and the Discovery of the Earth’s Antiquity” Jack Repcheck

1800 – The cooling Earth, Joseph Fourier

Joseph Fourier (1768-1830) French physicist and mathematician. He created mathematical tools that let us study how heat flows through solids.

Fourier’s studies of heat led him to argue that Earth’s history had a direction: beginning warm, and then cooling through time.

1815 – The Map That Changed the World

“William Smith and the Birth of Modern Geology,” by Simon Winchester

from a book review on Amazon:

Born to humble parents, Smith was also a child of the Industrial Revolution …While working as surveyor in a coal mine, Smith noticed the abrupt changes in the layers of rock as he was lowered into the depths. He came to understand that the different layers–in part as revealed by the fossils they contained – always appeared in the same order, no matter where they were found. He also realized that geology required a three-dimensional approach. William Smith spent the next 20 some years traveling throughout Britain, observing the land, gathering data, and chattering away about his theories to those he met along the way, thus acquiring the nickname “Strata Smith.”
In 1815 he published his masterpiece: an 8.5 by 6 foot, hand-tinted map revealing “A Delineation of the Strata of England and Wales.”
“Despite this triumph, Smith’s road remained more rocky than smooth. Snubbed by the gentlemanly Geological Society, Smith complained that “the theory of geology is in the possession of one class of men, the practice in another.”
Indeed, some members of the society went further than mere ostracism–they stole Smith’s work. These cartographic plagiarists produced their own map, remarkably similar to Smith’s, in 1819. Meanwhile the chronically cash-strapped Smith had been forced to sell his prized fossil collection and was eventually consigned to debtor’s prison.
In the end, the villains are foiled, our hero restored, and science triumphs. Winchester clearly relishes his happy ending, and his honey-tinged prose (“that most attractively lovable losterlike Paleozoic arthropod known as the trilobite”) injects a lot of life into what seems, on the surface, a rather dry tale.” – Sunny Delaney

One of his maps:

Map reproduced by permission of the British Geological Survey

British Geological Survey

Another of his maps:

“William Smith’s Geological section from London to Snowdon, showing the varieties of the strata, and the correct altitude of the hills by William Smith Civil Engineer 1817, is dated 15th July 1817.”

1830 Charles Lyell, Principles of Geology

Lyell started with the work of Hutton -> Rain erodes mountains, while molten rock pushes up to create new ones. The eroded sediments form into layers of rock, which can later be lifted above sea level, tilted by the force of the uprising rock, and eroded away again. These changes are tiny, but with enough time they could produce vast changes. Hutton therefore argued that the Earth was vastly old — a sort of perpetual-motion machine passing through regular cycles of destruction and rebuilding that made the planet suitable for mankind.

Charles Lyell (1797 – 1875) traveled through Europe to find more evidence that gradual changes, the same we can see happening today, had produced the features of the Earth’s surface. He found evidence for many rises and falls of sea level, and of giant volcanoes built on top of far older rocks. Processes such as earthquakes and eruptions, which had been witnessed by humans, were enough to produce mountain ranges. Valleys were not the work of giant floods but the slow grinding force of wind and water.

Charles Lyell’s version of geology came to be known as uniformitarianism, because of his fierce insistence that the processes that alter the Earth are uniform through time.

Lyell crafted a powerful lens for viewing the history of the Earth. On Darwin’s voyage aboard the Beagle, for example, Darwin was able to decipher the history of the Canary Islands (by applying Lyell’s ideas to the volcanic rock he encountered there. Today satellite measurements reveal that mountains may rise an inch a year, while radioactive clocks help show how they’ve been rising that way for millions of years. But Lyell could never have grasped the mechanism — plate tectonics — that makes this kind of geological change happen.

[Yet geologists today also know that some of the factors that changed the Earth in the past cannot be seen at work today. For example, the early Earth was pummeled by gigantic hunks of solar debris, some as big as Mars. For the first one or two billion years of Earth’s history, plate tectonics didn’t even exist as we know it today.]

Lyell had an equally profound effect on our understanding of life’s history. He influenced Darwin so deeply that Darwin envisioned evolution as a sort of biological uniformitarianism. Evolution took place from one generation to the next before our very eyes, he argued, but it worked too slowly for us to perceive.

from http://evolution.berkeley.edu/evolibrary/article/history_12

His most famous work: “Principles of Geology: Being an attempt to explain the former changes of the Earth’s surface, by reference to causes now in operation” Published in 3 volumes in 1830–1833.

1869 – Major John Wesley Powell and the Grand Canyon

Powell leads a scientific expedition down the Colorado River and through the Grand Canyon – provides evidence of Earth’s very long existence.

As seen from space!

The grand canyon from space
The grand canyon
The grand canyon
PBS American Experience: Lost In The Grand Canyon

“Lost in the Grand Canyon” – PBS series about Jown Wesley Powell’s Colorado River journey. It includes a timeline, maps, and program information. http://www.pbs.org/wgbh/amex/canyon/

1912 Alfred Wegener proposes theory of continental drift

Perhaps the most important discovery in Earth Science was the discovery that continents move (continental drift). Alfred Wegener (1880 – 1930) a German geophysicist and meteorologist, first published his theory on this in a lecture in Germany, in 1912.
drift 2

Wegener and continental drift

“Univ. of California Museum of Paleontlogy”


Five views of how Earth changes

1. Biblical Catastrophism

The world is said to have been created in only 7 days, the world is only 6,000 years old, the great flood of Noah killed off the dinosaurs, and this flood carved out all the valleys and canyons that we see today.

Noah global flood

2. Scientific catatrophism – Early 19th century.

French scientist Georges Cuvier examined the fossil record. He speculated that low-lying areas near the sea were flooded in aquatic catastrophes, causing the massive extinctions seen in the fossil record. But did not literally accept the story of Noah’s flood.

“Influenced by the Enlightenment and the intellectual climate of the French revolution, he avoided religious speculation …. Cuvier also believed that the stratigraphic record indicated that there had been several of these revolutions, which he viewed as recurring natural events, amid long intervals of stability during the history of life on earth. This led him to believe the Earth was several million years old.”


In the late 1700s. Abraham Gottlob Werner, proposed that all of the Earth’s rocks were formed by rapid chemical precipitation from a “world ocean,” which he then summarily disposed of in catastrophic fashion. This is part of an early scientific hypothesis called Neptunism. While this hypothesis was eventually disproven, note that this is how science advances: People study the world, and propose a testable explanation (hypothesis) for what we see. Subsequent research then informs us whether our hypothesis is correct or not. Werner’s observations and hypothesis making is certainly an important example of the scientific method in action.

3. Gradualism – Promoted by Hutton and Lyell.

Features of our world were not created by catastrophes. Rather, our world was gradually changed by natural processes, over very long periods of time. Canyons are slowly carved by rivers; new mountains built by continents slowly moving into each other; old mountains  are slowly eroding due to weather, etc.

4. Uniformitarianism builds on gradualism, and supports it with a set of ideas:

Uniformitarianism (the pre-20th century view) was based on these ideas:

* the same laws of nature that exist now also existed in the distant past

* the same geological and weather processes that occur now also occurred in the distant past

* continent-wide cataclysmic events, while very rare, occur as often now as they did in the past (*)

* planetary cataclysmic events do not exist. (*)

(*) These last two points have been modified in the modern synthesis (see below)

5. The modern synthesis: Gradualism, Uniformitarianism and – very rarely – catastrophism all occur.

Earth has developed gradually (gradualism), following laws of nature that uniformly exist in the past and present (uniformitarianism). Most features of our world indeed were formed very uniformly and gradually. However, there are rare, continent-wide and planetary catastrophic events that shape our world. These catastrophic evens include:

* Eruptions of megacalderas and supervolcanoes, which have continent-wide, and worldwide, effects

* Rare, monsterously large eruptions of basalt that create lava flood over areas greater than 100,000 square kilometer. These are called Large igneous provinces. They are associated with mass extinction events.

* Mega-thrust earthquakes

* Mega-floods (Ourburst floods) – for example, the Glacial lake outburst floods in North America (15,000 to 8,000 years ago)

* Mega-tsunamis – caused by giant landslides, or extra-terrestrial impact events in the ocean. (See the 1958 Lituya Bay megatsunami)

* comet or meteor impacts

* Massive glaciations/Ice ages.


Principles of Relative Dating: Ages of rocks and fossils

Lightly adapted from from https://yr11geology.wikispaces.com/geotime

Dating: How do we know when things happened?

There are several sorts of dating used by geologists: relative dating, radiometric dating and fossil dating.

Relative Dating

Consider this cross section, based on an area near Port Waikato.  (This is on the bank of the Waikato River, in New Zealand.)


The units on the key in the left are not shown in the correct order. Can you work them out? (answer down the page)

There are several rules we can use to work out the sequence:

The youngest is on the top:

1.  ‘Rule of superposition’.  Works even if the layers have been tilted or folded.
Applying this rule to the rocks above, the green sandstone ( only green on the diagram, not in real life) is the oldest rock, then the conglomerate, then the mudstone.

These rocks are folded (into an ‘anticline’), so you would not necessarily see the pattern at the surface we see above. Instead, you might see:


A geologist looks for bedding in the sedimentary rocks, which were originally horizontal.

Obscured rocks can be worked out. Example: What type of rock is under the landslide at ‘Q’? in the diagram? It is the siltstone, because it is above the mudstone and you can see it on the other side of the anticline. If you are walking along the road above from left to right, you would see the bedding go from dipping to the left on one side, to horizontal in the middle, to dipping to the right on the other side.

2. Unconformity 

If you look at the coal in the top sequence, you can see that it rests on the rocks below it at an angle. This ‘cutoff’ is called an unconformity.
It indicates a ‘gap’ in time – enough time for the sequence below it to be uplifted and eroded away to form the level surface you can see at the bottom of the coal.
This may mean that millions of years passed between the siltstone and the coal. The rocks that are in the bottom layers must eventually have sunk below the sea again before the next lot of sediments were laid down.

In fact, at Port Waikato where this section is based on, the sequence at the bottom was formed in the age of dinosaurs. The youngest rocks below the unconformity are about 140 million years old (from fossil evidence). The coal above the unconformity is about 100 million years younger – so this ‘gap’ represents a huge period of time in which New Zealand eroded away to a level, swampy plain (hence the coal) and then sank below the sea (forming the limestone).

There is a good picture of an actual unconformity in America here.

Unconformity between Popotosa Formation playa deposits and post-Santa Fe Group (Pleistocene or younger) alluvium, San Lorenzo Canyon area, north of Socorro, New Mexico.
{ http://geoinfo.nmt.edu/staff/scholle/graphics/Unconf.html }

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