Abraham Gottlob Werner's Neptunist Stratigraphy: An Incorrect Theory Advances the Geological Sciences

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Abraham Gottlob Werner's Neptunist Stratigraphy: An Incorrect Theory Advances the Geological Sciences

Overview

Abraham Gottlob Werner (1749-1817) is often remembered as the mistaken champion of a false theory about the structure of Earth's crust. However, his water-based hypothesis of the formation of rock strata was more than a wrong idea. Werner's theory was the first well-ordered geological description of the strata of Earth based on physical evidence that accounted for Earth's history. While his ideas were eventually overturned, often by his own students, he established a new way of thinking about the formation of Earth based on observation, experiment, and an attempt to understand historical geological processes.

Background

Earth's strata are the layers of various rock and mineral deposits that exist in a cross-section of Earth's crust. Strata look like the layers of a cut onion, or the side of a hamburger when you take a bite out of it. These layers are sometimes revealed by erosion, in the case of the Grand Canyon, or by landslides and man-made excavations.

The idea that water was the main force in the creation of Earth's surface dates back to at least the tenth-century Arab philosophers. In medieval Europe water-based theories became popular, as they explained the biblical flood of Noah. Such theories often received the blessing of the church, whereas other ideas could be condemned. The eighteenth century saw a new wave of water-based, or "neptunist," theories (after Neptune the ancient god of water). Many such theories took the Bible as their starting point, while others were based on abstract philosophical ideas or random notions. However, Werner's neptunist theory was an interpretation of the physical evidence that described the formation of Earth's crust as a long historical process.

Werner's family had a long association with iron-working, and his father was the inspector of the Duke of Solm's ironworks. Werner seemed destined to follow his father's career. However, while gaining the required legal education at the University of Leipzig, he became sidetracked by mineralogy. Werner abandoned his law degree in 1774, but by then he had published his first book, Von den äusserlichen Kennzeichen der Fossilien, which was a simple and orderly mineral identification manual. On the strength of this book Werner secured a teaching position at the Mining Academy at Freidburg in Saxony. He remained there for the rest of his life, developing and teaching his theory of the origin of the strata of Earth.

Werner's theory was not completely original. He combined several popular ideas, in particular the work of Johann Gottlob Lehmann (1719-1767) and Georg Christian Füchsel (1722-1773). Lehmann had stressed the importance of the order of rock strata and used the practical knowledge of quarrymen and miners to formulate his theories. Füchsel suggested that strata were formed successively over time.

Werner's theory added the new dimension of a historical explanation for the observable strata. Firmly basing his theory on the geological knowledge of his day, he proposed a global scheme that accounted for the origin and distribution of the entire Earth's surface. Werner proposed that the rock layers of Earth had been laid down at different times by an all-encompassing, universal ocean. The rocks that made up the crust of Earth had been formed from particles that settled out of the murky universal ocean, as precipitates or sediments. The differences in rock type and layering visible in the world were explained by rises and falls in the level of the universal ocean, as well as the turbulence or calmness of the waters.

Werner's first version of his theory broke down history into four periods: the primitive, floetz, volcanic, and alluvial, each with specific conditions to explain the rock types formed. In the primitive period, for example, the universal ocean was deep and calm, producing a solidly packed, smoothly distributed granite layer. Later the waters became more turbulent, so later rocks were less smoothly distributed. No life was supposed to have existed in the primitive period, so granite rocks must be free of fossils.

Impact

Werner's ideas had immediate and wide appeal. The theory was a simple yet elegant explanation of the evidence, unlike many rival theories that seemed to disregard observations. The theory appeared complete, and a number of very successful predictions were made from it. Unlike theories that merely described a localized region, Werner's concept explained the strata of the whole Earth. At the same time, the theory was flexible enough to account for local variations. With additional after-effects, such as cave-ins and erosion, the theory could explain virtually all the geological phenomena observable in Werner's time.

The theory was also flexible in the sense that Werner was prepared to modify the exact details to accommodate new evidence. Without abandoning the fundamentals, Werner and his pupils explained away seemingly contrary data with new twists to the basic concept. For example, Werner added a new age, the transitional period, to explain the presence of fossils in some granite deposits. Instead of threatening the theory, contrary observations were used to help refine the overall concept.

Unlike many earlier theorists on the formation of Earth, Werner did not feel compelled to make his theory fit the biblical creation. His ideas implied that Earth was over a million years old, to allow time for the formation of rocks by the slow processes of sedimentation and precipitation from the universal ocean. This time span was far greater than the calculations of biblical scholars, who suggested about 6,000 years. Yet Werner was not attacked by church authorities, as his concept of a universal ocean was taken by many as supporting evidence of the biblical flood. Indeed, Werner's theory was championed by many religious figures long after it had ceased to be used by geologists.

Werner wrote down few of his ideas and published even fewer. His most influential work, Kurze Klassifikation und Beschreibung der verschiedenen Gebirgsarten, was finished in 1777 but not published until 1786, and it was only 28 pages long. He never published a complete version of his theory, and it was only through unpublished documents and the lecture notes of his students that a full theory was reconstructed. Werner's lecturing was enthusiastic and engaging. He had a personal magnetism that attracted students from all over Europe and beyond. His teaching produced large numbers of eager disciples who spread the gospel of Wernerian neptunism.

Despite the popularity of Werner and his ideas, there was no shortage of critics. The perceptive Italian Scipione Breislak (1750-1826) asked where all the water had gone. Werner suggested outer space but gave no reason. The theory was also criticized for not explaining the formation of the entire Earth, only the crust.

There was opposition to neptunism in general. Many Italian and French scientists were convinced that volcanic action, not water, was responsible for rock formation. A division developed between vulcanists—named after Vulcan, the ancient god of volcanoes—and neptunists that was partly to do with the geography native to each scientist. Particularly active volcanic regions, such as the Italian peninsula, tended to produce vulcanists, whereas in England and the German states local geology produced supporters of neptunism.

In his Kurze Klassifikation booklet Werner declared all basalt to be of watery origin, sparking the great basalt controversy. Basalt is a common and widely distributed rock type, so it was keenly debated whether fire or water was the key creative agent. Werner regarded volcanoes as recent events, giving them no role in the historical formation of Earth's deeper strata. The local strata of Saxony seemed to support his ideas, or at least not contradict them. Werner's poor health meant he could not travel, and so the vast majority of his supporting evidence came from his immediate surroundings. However, this did not stop Werner from proposing that his stratigraphy applied to the entire surface of Earth.

A number of Werner's students were inspired to go further afield and gather evidence from other regions, which they hoped would support their teacher's theories. However, for many the effect was to turn them away from Werner's ideas. After visiting volcanic areas in Europe, Jean François d'Aubuisson de Voisins (1769-1819) became convinced that neptunism was incorrect. "The facts which I saw spoke too plainly to be mistaken," he wrote, "the truth revealed itself before my eyes." For Leopold von Buch (1774-1853) the volcanic rocks around Rome sowed the first seeds of doubt, and later trips to Scandinavia converted him completely. Alexander von Humboldt (1769-1859) traveled all over South America trying to find supporting evidence for Werner, but again his observations persuaded him otherwise. It is to Werner's credit as a teacher that his own students, who had originally gone out to prove him right, allowed the evidence to shape their conclusions.

Die-hard supporters of Werner's ideas tried to accommodate the new observations into the theory by adding more and more fluctuations in the universal ocean. However, the theory began to lose its simplicity and overall structure. Other theories, such as James Hutton's plutonism (after Pluto the god of the underworld), which stressed the role of underground heat in rock formation, began to gain in popularity as Werner's faded. Neptunism continued to be taught in Germany after Werner's death, and also remained popular in England. However, by the mid-1820s neptunism was all but dead.

Werner's lasting legacy to geology was his approach to the field, not the form his theory took. His stress on explaining physical evidence, and the sense of history he injected into geological theories, gave the science a new direction. He passed his passion for the field to his students, many of whom, ironically, used the skills they had been taught to overturn their master's theories.

DAVID TULLOCH