History of geology

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The history of geology is concerned with the development of the natural science of geology. Geology is the scientific study of the origin, history, and structure of the Earth. ^[1] Throughout the ages geology provides essential theories and data that shape how society conceptualizes the Earth. Ancient Greece developed the primary geological concepts concerning the origin of the Earth. ^[2] Additionally, in the 4th century BC Aristotle made critical observations of the slow rate of geological change.^[3] During the 17th century the heated debate between religion and science over the Earth’s origin further propelled interest in the Earth and brought about more systematic identification techniques of the Earth’s strata.^[4] The Earth’s strata can be defined as horizontal layers of rock having approximately the same composition throughout.^[5]

The popular mining industry during the 18th century both increased social interest and drove scientists to form more systematic and detailed studies of the composition of the Earth’s strata. From the increased societal interest of geology, in 1741 it became a specific field of study to be taught at the National Museum of Natural History in France.^[6] The controversial topic of the Earth’s origin continued to circulate between religious and scientific circles. Two feuding theories developed to explain the Earth’s origin with designated followers: the Neptunists whose theory supported that of the Bible’s Great Flood and the Plutonists who believed the Earth gradually formed over an immeasurable amount of time.^[7]

The dialogue about the creation of the Earth occurring within the scientific community during the 19th century drove the development of the stratigraphical column; many of the concepts behind this invention can be attributed to William Smith, Georges Cuvier and Alexander Broignart.^[8] Also in this period, imperialism motivated countries to sponsor voyages of exploration to distant lands. Charles Darwin made geological observations on such a voyage, providing evidential support of his revolutionary theory of evolution.^[9] Again a religious debate ensued; two conflicting groups, uniformitarians and catastrophists, argued over the age of the Earth.^[10] Charles Lyell, an influential uniformitarian, published his book in 1830 the “Principles of Geology” which proposed that the Earth changes very gradually and is immeasurably old.^[11]

The theory of Continental Drift was proposed in 1912 by Alfred Wegener.^[12] This idea, unaccepted at the time, suggested a method of continental movement that occurred throughout history.^[13] Supporting evidence of Continental Drift, including seafloor spreading and paleomagnetism, justified the theory of Continental Drift, which in the late 1960s was replaced and encompassed by Plate Tectonics.^[14] In the latter half of the 20th century the approach to the study of geology changed to evaluating the Earth in a broader perspective.^[15] To coincide with this perspective, satellites were first used in the 1970s and are still currently in use by the Landsat Program to produce images of the Earth that can be geologically studied.^[16]

[edit] Origins of geology

The foundations of geology trace back to that of the Ancient Greeks. Some of the first geological thoughts were about the origin of the Earth. With a lack of knowledge and technology, ancient philosophers created mythical stories and proposed theories to explain how the Earth came to be. One of the philosophers who observed the composition of the land and formulated a theory with some supporting evidence was Aristotle in the 4th Century BC.^[17] From his observations he determined that the Earth changes, and that it does so at such a slow rate that these changes can not be observed during one person’s lifetime.^[18] Aristotle developed one of the first evidentially based concepts connected to the geological realm regarding the rate at which the Earth physically changes.^[19] Unfortunately, this concept of change was too unbelievable for the public to embrace and Aristotle’s theories on the Earth were dismissed.

[edit] 17th century

A portrait of Whiston with a diagram demonstrating his theories of cometary catastrophism best described in A New Theory of the Earth

It was not until the 17th century that geology made great strides in its development. At this time, geology became its own entity in the world of natural science. It was discovered by the Christian world that different translations of the Bible contained different versions of the biblical text. The one entity that remained consistent through all of the interpretations was that the Deluge had formed the world’s geology and geography.^[20] To prove the Bible’s authenticity, individuals felt the need to demonstrate with scientific evidence that the Great Flood had in fact occurred. With this enhanced desire for data came an increase in observations of the Earth’s composition, which in turn led to the discovery of fossils. Although theories that resulted from the heightened interest in the Earth’s composition were often manipulated to support the concept of the Deluge, a genuine outcome was a greater interest in the makeup of the Earth. Due to the strength of Christian beliefs during the 17th century, the theory of the origin of the Earth that was most widely accepted was A New Theory of the Earth published in 1696, by William Whiston.^[21] Whiston used Christian reasoning to “prove” that the Great Flood had occurred and that the flood had formed the rock strata of the Earth.

[edit] 18th century

From this increased interest in the nature of the Earth and its origin, came a rise in the interest of minerals and other components of the Earth’s crust. Moreover, the increasing commercial importance of mining in Europe during the mid to late 18th century made the possession of accurate knowledge about ores and their natural distribution essential.^[22] Scholars began to study the makeup of the Earth in a systematic manner, with detailed comparisons and descriptions not only of the land itself, but of the semi-precious metals that had such great value. For example, in 1774 Abraham Gottlob Werner published the book “On the External Characters of Minerals,” which brought him widespread recognition because he presented a detailed system for identifying specific minerals based on external characteristics.^[23] The more efficiently that productive land for mining could be found and that the semi-precious metals could be identified, the more money that could be made. This drive for economic success fueled geology into the limelight and made it a popular subject to pursue. With an increased number of people studying it, came more detailed observations and more information about the Earth.

During the eighteenth century, the story of the history of the Earth; namely the religious concept versus factual evidence once again became a popular discussion in society. In 1749 the French naturalist Georges-Louis Leclerc, Comte de Buffon published his “Histoire Naturelle” in which he attacked the popular Christian concepts of Whiston and other Christian theorists on the topic of the history of the Earth.^[24] From experimentation with cooling globes, he found that the age of the Earth was not 6,000 years as stated in the Bible, but rather 75,000 years.^[25] Another individual who attributed the history of the Earth to neither God nor the Bible was the philosopher Immanuel Kant who published this concept in 1755 in his “Allgemeine Naturgeshichte und Theories des Himmels.”^[26] From the works of these educated men, as well as others, it became acceptable by the mid eighteenth century to question the age of the Earth. This questioning represented a turning point in the study of the Earth. It was now possible to study the history of the Earth from a scientific perspective rather than a religious one.

With science as a driving force behind the investigation of the Earth’s history, the study of geology could now become a distinct field of science. First, the terminology and definition of what geological study consisted of had to be determined. The term geology was first used professionally in publications by two Genevian naturalists, Jean-Andre Deluc and Horace-Benedict de Saussure.^[27] Geology was not well received as a term until it was used in the very popular encyclopedia, the “Encyclopedie,” published in 1751 by Denis Diderot.^[28] Once the term was coined as the study of the Earth and its history, geology slowly became a more prevalent and recognized science of its own standing that could be taught as a field of study at educational institutions. In 1741 the most well-known institution in the field of natural history, the National Museum of Natural History in France designated the first teaching position specifically for geology.^[29] This was an important step in the further development of geology as a science and in the recognition of the importance of widely distributing this knowledge.

After the designation of geology as a specific field of study in an institution, this subject flourished in educated society. By the 1770s two feuding theories with designated followers were established. These contrasting theories explained how the rock layers of the Earth’s surface had formed. The German geologist, Abraham Werner proposed the theory that the Earth’s layers, including basalt and granite, had formed as a precipitate from an ocean that covered the entire Earth, referring to the Deluge. Werner’s system was influential and those that believed his theory were known as Neptunists.^[30] The Scottish naturalist, James Hutton, argued against the theory of Neptunism. Hutton proposed the theory of Plutonism; the Earth formed through the gradual solidification of a molten mass at a slow rate by the same processes that occurred throughout history and continues in present day. This led him to the conclusion that the Earth was immeasurably old and could not possibly fit within the limits of the Bible’s 6,000 years. Plutonists believed that volcanic processes were the chief agent in rock formation, not water from a Great Flood.^[31]

[edit] 19th century

Engraving from William Smith's 1815 monograph on identifying strata by fossils

The Neptunists and Plutonists supplied necessary data to help complete the stratigraphical column in the early 19th century. The stratigraphical column can be defined as “the sequence of rock formations arranged according to their order of formation in time.”^[32] William Smith, Georges Cuvier and Alexander Broignart can all be recognized for their roles during this century in furthering the concept of fossil-based stratigraphy. The English mineral surveyor William Smith found empirically that fossils were a highly effective means of distinguishing between otherwise similar formations of the landscape. At about the same time, the French comparative anatomist Georges Cuvier realized that the relative ages of fossils could be determined from a geological standpoint; in terms of what layer of rock the fossils are located and the distance these layers of rock are from the surface of the Earth. Cuvier’s mineralogist colleague Alexandre Brogniart augmented Cuvier’s practices. Through the synthesis of these findings, Brogniart and Cuvier realized that different strata could be identified by fossil contents and thus each stratum could be assigned to a unique position in a sequence.^[33] After the publication of Cuvier and Broignart’s book, “Description Geologiques des Environs de Paris” in 1811, which outlined the concept of stratigraphy, came a great interest in this new method.^[34] Stratigraphy became very popular amongst geologists; many hoped to apply this concept to all the rocks of the Earth. During this century various geologists further refined the stratigraphical column to completion. For instance, in 1833 while Adam Sedgwick was mapping rocks that he established were from the Cambrian Period, Charles Lyell was suggesting a subdivision of the Tertiary Period.^[35] The stratigraphical column was significant because it now supplied a method to date the relative age of all rocks by assigning them to different positions in the stratigraphical column. This created a global method of dating the age of the Earth and allowed for further correlations to be drawn from similarities found in the makeup of the Earth’s crust in various countries.

During the same time that the stratigraphical column was being completed, imperialism drove several countries in the early to mid 19th century to explore distant lands to expand their empires. This gave naturalists the opportunity to collect data on these voyages. One British naturalist, Charles Darwin, had great influence on society from the data he collected and observations he made during his voyage. Darwin read on his voyage Lyell’s book the “Principles of Geology” and was converted to a uniformitarian. With this idea in mind he made geological observations that supported the concept of Uniformitarianism; that throughout history the world changed at a very gradual rate. From such geological observations Darwin was able to deduce the revolutionary theory of evolution with the publication of his book “The Origin of Species” in 1859.^[36]

The Uniformitarian-Catastrophist debate formed the centerpiece of the geological religion versus science discussion during the nineteenth-century. Catastrophists defended the concept of the biblical Great Flood and is the axiom that certain vast geological changes in the Earth's history were caused by catastrophes rather than gradual processes.^[37] Charles Lyell challenged this approach in the publication of his book in 1802, “Principles of Geology,” which presented a variety of geological evidence from England, France, Italy and Spain to prove Hutton’s ideas of gradualism correct.^[38] He argued that most geological change had been very gradual in human history. Lyell provided evidence for Uniformitarianism; a geological doctrine that processes occur at the same rates in the present as they did in the past and account for all of the Earth’s geological features.^[39] Lyell’s works were popular and widely read, the concept of Uniformitarianism had taken a strong hold in geological society.^[40]

Economic motivations for the practical use of geological data caused governments to support geological research. During the 19th century the governments of several countries including Canada, Australia, Great Britain and the United States funded geological surveying that would produce geological maps of vast areas of the countries. Geological surveying provides the location of useful minerals and such information could be used to benefit the country’s mining industry. With the government funding of geological research, more individuals could study geology with better technology and techniques, leading to the expansion of the field of geology.^[41]

In the 19th century, scientific realms established the age of the Earth in terms of millions of years. By the early 20th century the Earth’s estimated age was 2 billion years. Radiometric dating determined the age of minerals and rocks, which provided necessary data to help determine the Earth’s age.^[42] With this new discovery based on verifiable scientific data and the possible age of the Earth extending billions of years, the dates of the geological time scale could now be refined. Theories that did not comply with the scientific evidence that established the age of the Earth could no longer be accepted.

[edit] 20th century

The determined age of the Earth as 2 billion years opened doors for theories of continental movement during this vast amount of time.^[43] In 1912 Alfred Wegener proposed the theory of Continental Drift.^[44] This theory suggests that the continents were joined together at a certain time in the past and formed a single landmass known as Pangaea; thereafter they drifted like rafts over the ocean floor, finally reaching their present position. Evidence such as the shapes of continents supported the idea of continental drift because when coastline geography was compared between continents it seemed probable that they could have fit together to form the single landmass of Pangaea. Additionally, the theory of continental drift offered a possible explanation as to the formation of mountains. From this, different theories developed as to how mountains were built. Unfortunately, Wegner’s ideas were not accepted during his lifetime and his theory of Continental Drift was not accepted until the 1960s.^[45]

In the 1960s new found evidence supported the theory of Continental Drift. The term Continental Drift was no longer used but was replaced by the concept of Plate Tectonics that was well supported and accepted by almost all geologists by the end of the decade. Geophysical evidence accumulated that dated the Earth at 4.6 billion years, suggesting lateral motion of continents and indicating a young age of the oceanic crust. This geophysical evidence included the hypotheses of seafloor spreading and paleomagnetism. The hypothesis of seafloor spreading, proposed by Robert S. Dietz and Harry H. Hess, holds that the oceanic crust forms as the seafloor spreads apart along mid-ocean ridges. Paleomagnetism is the record of the orientation of the Earth’s magnetic field recorded in rocks. British geophysicist S. Runcorm suggested the concept of paleomagnetism from his finding that the continents had moved relative to one another in respect to the Earth’s magnetic poles.^[46]

[edit] Modern geology

In recent years, geology has continued its tradition as the study of the character and origin of the Earth, its surface features and internal structure. What changed in the later 20th century is the perspective of geological study. Geology was now studied using a more integrative approach, considering the Earth in a broader context encompassing the atmosphere, biosphere and hydrosphere.^[47] Satellites located in space that take wide scope photographs of the Earth provide such a perspective. In 1972, The Landsat Program, a series of satellite missions jointly managed by NASA and the U.S. Geological Survey, began supplying satellite images that can be geologically analyzed. For geology these images can be used to map major geological units, recognize and correlate rock types for vast regions and track the movements of Plate Tectonics. A few societal applications of this data include the ability to produce geologically detailed maps, locate sources of natural energy and predict possible natural disasters caused by plate shifts.^[48]

[edit] See also

• Economic geology
• Flood geology
• Geology
• Geodesy
• Geography
• Historical geology
• History of palaeontology
• History of science
• Humboldtian science
• Natural history
• Natural philosophy
• Nicolas Steno

[edit] Notes and references

[edit] External links

http://geology.com

http://landsat.gsfc.nasa.gov