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Monday, April 22, 2019

Georges Cuvier

From Wikipedia, the free encyclopedia

Georges Cuvier

Georges Cuvier.png
Born23 August 1769
Died13 May 1832 (aged 62)
NationalityFrench
Known forLe Règne Animal; establishing the fields of stratigraphy and comparative anatomy, and the principle of faunal succession in the fossil record; making extinction an accepted scientific phenomenon; opposing theories of evolution
Scientific career
FieldsNatural history, paleontology, anatomy
InstitutionsMuséum national d'histoire naturelle
Author abbrev. (botany)Cuvier

Jean Léopold Nicolas Frédéric, Baron Cuvier (French: [kyvje]; 23 August 1769 – 13 May 1832), known as Georges Cuvier, was a French naturalist and zoologist, sometimes referred to as the "founding father of paleontology". Cuvier was a major figure in natural sciences research in the early 19th century and was instrumental in establishing the fields of comparative anatomy and paleontology through his work in comparing living animals with fossils.

Cuvier's work is considered the foundation of vertebrate paleontology, and he expanded Linnaean taxonomy by grouping classes into phyla and incorporating both fossils and living species into the classification. Cuvier is also known for establishing extinction as a fact—at the time, extinction was considered by many of Cuvier's contemporaries to be merely controversial speculation. In his Essay on the Theory of the Earth (1813) Cuvier proposed that now-extinct species had been wiped out by periodic catastrophic flooding events. In this way, Cuvier became the most influential proponent of catastrophism in geology in the early 19th century. His study of the strata of the Paris basin with Alexandre Brongniart established the basic principles of biostratigraphy.

Among his other accomplishments, Cuvier established that elephant-like bones found in the USA belonged to an extinct animal he later would name as a mastodon, and that a large skeleton dug up in Paraguay was of Megatherium, a giant, prehistoric ground sloth. He named the pterosaur Pterodactylus, described (but did not discover or name) the aquatic reptile Mosasaurus, and was one of the first people to suggest the earth had been dominated by reptiles, rather than mammals, in prehistoric times.

Cuvier is also remembered for strongly opposing theories of evolution, which at the time (before Darwin's theory) were mainly proposed by Jean-Baptiste de Lamarck and Geoffroy Saint-Hilaire. Cuvier believed there was no evidence for evolution, but rather evidence for cyclical creations and destructions of life forms by global extinction events such as deluges. In 1830, Cuvier and Geoffroy engaged in a famous debate, which is said to exemplify the two major deviations in biological thinking at the time – whether animal structure was due to function or (evolutionary) morphology. Cuvier supported function and rejected Lamarck's thinking.

His most famous work is Le Règne Animal (1817; English: The Animal Kingdom). In 1819, he was created a peer for life in honor of his scientific contributions. Thereafter, he was known as Baron Cuvier. He died in Paris during an epidemic of cholera. Some of Cuvier's most influential followers were Louis Agassiz on the continent and in the United States, and Richard Owen in Britain. His name is one of the 72 names inscribed on the Eiffel Tower.

Biography

Portrait by François-André Vincent, 1795
 
Cuvier was born in Montbéliard, France (in department of Doubs), where his Protestant ancestors had lived since the time of the Reformation. His mother was Anne Clémence Chatel; his father, Jean George Cuvier, was a lieutenant in the Swiss Guards and a bourgeois of the town of Montbéliard. At the time, the town, which was annexed to France on 10 October 1793, belonged to the Duchy of Württemberg. His mother, who was much younger than his father, tutored him diligently throughout his early years, so he easily surpassed the other children at school. During his gymnasium years, he had little trouble acquiring Latin and Greek, and was always at the head of his class in mathematics, history, and geography. According to Lee, "The history of mankind was, from the earliest period of his life, a subject of the most indefatigable application; and long lists of sovereigns, princes, and the driest chronological facts, once arranged in his memory, were never forgotten." 

Birthplace of Georges Cuvier in Montbéliard
 
At the age of 10, soon after entering the gymnasium, he encountered a copy of Conrad Gessner's Historiae Animalium, the work that first sparked his interest in natural history. He then began frequent visits to the home of a relative, where he could borrow volumes of the Comte de Buffon's massive Histoire Naturelle. All of these he read and reread, retaining so much of the information, that by the age of 12, "he was as familiar with quadrupeds and birds as a first-rate naturalist." He remained at the gymnasium for four years. 

Cuvier spent an additional four years at the Caroline Academy in Stuttgart, where he excelled in all of his coursework. Although he knew no German on his arrival, after only nine months of study, he managed to win the school prize for that language. Cuvier's German education exposed him to the work of the geologist Abraham Gottlob Werner (1750 - 1817), whose Neptunism and emphasis on the importance of rigorous, direct observation of three-dimensional, structural relationships of rock formations to geological understanding provided models for Cuvier's scientific theories and methods.

Upon graduation, he had no money on which to live as he awaited appointment to an academic office. So in July 1788, he took a job at Fiquainville chateau in Normandy as tutor to the only son of the Comte d'Héricy, a Protestant noble. There, during the early 1790s, he began his comparisons of fossils with extant forms. Cuvier regularly attended meetings held at the nearby town of Valmont for the discussion of agricultural topics. There, he became acquainted with Henri Alexandre Tessier (1741–1837), who had assumed a false identity. Previously, he had been a physician and well-known agronomist, who had fled the Terror in Paris. After hearing Tessier speak on agricultural matters, Cuvier recognized him as the author of certain articles on agriculture in the Encyclopédie Méthodique and addressed him as M. Tessier. 

Tessier replied in dismay, "I am known, then, and consequently lost."—"Lost!" replied M. Cuvier, "no; you are henceforth the object of our most anxious care." They soon became intimate and Tessier introduced Cuvier to his colleagues in Paris—"I have just found a pearl in the dunghill of Normandy", he wrote his friend Antoine-Augustin Parmentier. As a result, Cuvier entered into correspondence with several leading naturalists of the day, and was invited to Paris. Arriving in the spring of 1795, at the age of 26, he soon became the assistant of Jean-Claude Mertrud (1728–1802), who had been appointed to the newly created chair of comparative anatomy at the Jardin des Plantes.

The Institut de France was founded in the same year, and he was elected a member of its Academy of Sciences. On 4 April 1796 he began to lecture at the École Centrale du Pantheon and, at the opening of the National Institute in April, he read his first paleontological paper, which subsequently was published in 1800 under the title Mémoires sur les espèces d'éléphants vivants et fossiles. In this paper, he analyzed skeletal remains of Indian and African elephants, as well as mammoth fossils, and a fossil skeleton known at that time as the 'Ohio animal'. 

Cuvier's analysis established, for the first time, the fact that African and Indian elephants were different species and that mammoths were not the same species as either African or Indian elephants, so must be extinct. He further stated that the 'Ohio animal' represented a distinct and extinct species that was even more different from living elephants than mammoths were. Years later, in 1806, he would return to the 'Ohio animal' in another paper and give it the name, "mastodon". 

In his second paper in 1796, he described and analyzed a large skeleton found in Paraguay, which he would name Megatherium. He concluded this skeleton represented yet another extinct animal and, by comparing its skull with living species of tree-dwelling sloths, that it was a kind of ground-dwelling giant sloth

Together, these two 1796 papers were a seminal or landmark event, becoming a turning point in the history of paleontology, and in the development of comparative anatomy, as well. They also greatly enhanced Cuvier's personal reputation and they essentially ended what had been a long-running debate about the reality of extinction

In 1799, he succeeded Daubenton as professor of natural history in the Collège de France. In 1802, he became titular professor at the Jardin des Plantes; and in the same year, he was appointed commissary of the institute to accompany the inspectors general of public instruction. In this latter capacity, he visited the south of France, but in the early part of 1803, he was chosen permanent secretary of the department of physical sciences of the Academy, and he consequently abandoned the earlier appointment and returned to Paris. In 1806, he became a foreign member of the Royal Society, and in 1812, a foreign member of the Royal Swedish Academy of Sciences. In 1812 he became a correspondent for the Royal Institute of the Netherlands, and became member in 1827. Cuvier was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1822.

Cuvier's tomb in the Père Lachaise Cemetery, Paris
 
Cuvier then devoted himself more especially to three lines of inquiry: (i) the structure and classification of the Mollusca; (ii) the comparative anatomy and systematic arrangement of the fishes; (iii) fossil mammals and reptiles and, secondarily, the osteology of living forms belonging to the same groups. 

In 1812, Cuvier made what the cryptozoologist Bernard Heuvelmans called his "Rash dictum": he remarked that it was unlikely that any large animal remained undiscovered. Ten years after his death, the word "dinosaur" would be coined by Richard Owen in 1842. 

During his lifetime, Cuvier served as an imperial councilor under Napoleon, president of the Council of Public Instruction and chancellor of the university under the restored Bourbons, Grand Officer of the Legion of Honour, a Peer of France, Minister of the Interior, and president of the Council of State under Louis Philippe. He was eminent in all these capacities, and yet the dignity given by such high administrative positions was as nothing compared to his leadership in natural science.

Cuvier was by birth, education, and conviction a devout Lutheran, and remained Protestant throughout his life while regularly attending church services. Despite this, he regarded his personal faith as a private matter; he evidently identified himself with his confessional minority group when he supervised governmental educational programs for Protestants. He also was very active in founding the Parisian Biblical Society in 1818, where he later served as a vice president. From 1822 until his death in 1832, Cuvier was Grand Master of the Protestant Faculties of Theology of the French University.

Scientific ideas and their impact

Saartjie Baartman Remains

Saartjie Baartman died in December 1815 and was relocated to Paris, where she was dissected by Georges Cuvier. Cuvier examined Baartman's vagina and labia and concluded that they were not similar to monkeys' genitals. However, he concluded that her buttock was more similar to a female baboon or mandrill than to a European woman's. He believed her skull to be representative of the mix between a Negro and Mongol, but more similar to a monkey skull than any other human skull.

Her remains were displayed in the Musée de l’Homme in Paris until 1970, then were put into storage. Her remains were returned to South Africa in 2002. 

Opposition to evolution

Cuvier was critical of theories of evolution, in particular those proposed by his contemporaries Lamarck and Geoffroy Saint-Hilaire, which involved the gradual transmutation of one form into another. He repeatedly emphasized that his extensive experience with fossil material indicated one fossil form does not, as a rule, gradually change into a succeeding, distinct fossil form. A deep-rooted source of his opposition to the gradual transformation of species was his goal of creating an accurate taxonomy based on principles of comparative anatomy. Such a project would become impossible if species were mutable, with no clear boundaries between them. According to the University of California Museum of Paleontology, "Cuvier did not believe in organic evolution, for any change in an organism's anatomy would have rendered it unable to survive. He studied the mummified cats and ibises that Geoffroy had brought back from Napoleon's invasion of Egypt, and showed they were no different from their living counterparts; Cuvier used this to support his claim that life forms did not evolve over time."

Cuvier with a fish fossil
 
He also observed that Napoleon's expedition to Egypt had retrieved animals mummified thousands of years previously that seemed no different from their modern counterparts. "Certainly", Cuvier wrote, "one cannot detect any greater difference between these creatures and those we see, than between the human mummies and the skeletons of present-day men."

Lamarck dismissed this conclusion, arguing that evolution happened much too slowly to be observed over just a few thousand years. Cuvier, however, in turn criticized how Lamarck and other naturalists conveniently introduced hundreds of thousands of years "with a stroke of a pen" to uphold their theory. Instead, he argued that one may judge what a long time would produce only by multiplying what a lesser time produces. Since a lesser time produced no organic changes, neither, he argued, would a much longer time. Moreover, his commitment to the principle of the correlation of parts caused him to doubt that any mechanism could ever gradually modify any part of an animal in isolation from all the other parts (in the way Lamarck proposed), without rendering the animal unable to survive. In his Éloge de M. de Lamarck (Praise for M. de Lamarck), Cuvier wrote that Lamarck's theory of evolution
rested on two arbitrary suppositions; the one, that it is the seminal vapor which organizes the embryo; the other, that efforts and desires may engender organs. A system established on such foundations may amuse the imagination of a poet; a metaphysician may derive from it an entirely new series of systems; but it cannot for a moment bear the examination of anyone who has dissected a hand, a viscus, or even a feather.
Instead, he said, the typical form makes an abrupt appearance in the fossil record, and persists unchanged to the time of its extinction. Cuvier attempted to explain this paleontological phenomenon he envisioned (which would be readdressed more than a century later by "punctuated equilibrium") and to harmonize it with the Bible. He attributed the different time periods he was aware of as intervals between major catastrophes, the last of which is found in Genesis.

Cuvier's claim that new fossil forms appear abruptly in the geological record and then continue without alteration in overlying strata was used by later critics of evolution to support creationism, to whom the abruptness seemed consistent with special divine creation (although Cuvier's finding that different types made their paleontological debuts in different geological strata clearly did not). The lack of change was consistent with the supposed sacred immutability of "species", but, again, the idea of extinction, of which Cuvier was the great proponent, obviously was not.

Many writers have unjustly accused Cuvier of obstinately maintaining that fossil human beings could never be found. In his Essay on the Theory of the Earth, he did say, "no human bones have yet been found among fossil remains", but he made it clear exactly what he meant: "When I assert that human bones have not been hitherto found among extraneous fossils, I must be understood to speak of fossils, or petrifactions, properly so called". Petrified bones, which have had time to mineralize and turn to stone, are typically far older than bones found to that date. Cuvier's point was that all human bones found that he knew of, were of relatively recent age because they had not been petrified and had been found only in superficial strata. He was not dogmatic in this claim, however; when new evidence came to light, he included in a later edition an appendix describing a skeleton that he freely admitted was an "instance of a fossil human petrifaction".

The harshness of his criticism and the strength of his reputation, however, continued to discourage naturalists from speculating about the gradual transmutation of species, until Charles Darwin published On the Origin of Species more than two decades after Cuvier's death.

Extinction

Early in his tenure at the National Museum in Paris, Cuvier published studies of fossil bones in which he argued that they belonged to large, extinct quadrupeds. His first two such publications were those identifying mammoth and mastodon fossils as belonging to extinct species rather than modern elephants and the study in which he identified the Megatherium as a giant, extinct species of sloth. His primary evidence for his identifications of mammoths and mastodons as separate, extinct species was the structure of their jaws and teeth. His primary evidence that the Megatherium fossil had belonged to a massive sloth came from his comparison of its skull with those of extant sloth species.

Cuvier wrote of his paleontological method that "the form of the tooth leads to the form of the condyle, that of the scapula to that of the nails, just as an equation of a curve implies all of its properties; and, just as in taking each property separately as the basis of a special equation we are able to return to the original equation and other associated properties, similarly, the nails, the scapula, the condyle, the femur, each separately revel the tooth or each other; and by beginning from each of them the thoughtful professor of the laws of organic economy can reconstruct the entire animal." However, Cuvier's actual method was heavily dependent on the comparison of fossil specimens with the anatomy of extant species in the necessary context of his vast knowledge of animal anatomy and access to unparallelled natural history collections in Paris. This reality, however, did not prevent the rise of a popular legend that Cuvier could reconstruct the entire bodily structures of extinct animals given only a few fragments of bone.

At the time Cuvier presented his 1796 paper on living and fossil elephants, it was still widely believed that no species of animal had ever become extinct. Authorities such as Buffon had claimed that fossils found in Europe of animals such as the woolly rhinoceros and the mammoth were remains of animals still living in the tropics (i.e. rhinoceros and elephants), which had shifted out of Europe and Asia as the earth became cooler.

Thereafter, Cuvier performed a pioneering research study on some elephant fossils excavated around Paris. The bones he studied, however, were remarkably different from the bones of elephants currently thriving in India and Africa. This discovery led Cuvier to denounce the idea that fossils came from those that are currently living. The idea that these bones belonged to elephants living - but hiding - somewhere on Earth seemed ridiculous to Cuvier because it would be nearly impossible to miss them due to their enormous size. The Megatherium provided another compelling datapoint for this argument. Ultimately, his repeated identification of fossils as belonging to species unknown to man, combined with mineralogical evidence from his stratigraphical studies in Paris, drove Cuvier to the proposition that the abrupt changes the Earth underwent over a long period of time caused some species to go extinct.

Cuvier's theory on extinction has met opposition from other notable natural scientists like Darwin and Charles Lyell. Unlike Cuvier, they didn't believe that extinction was a sudden process; they believed that like the Earth, animals collectively undergo gradual change as a species. This differed widely from Cuvier's theory, which seemed to propose that animal extinction was catastrophic. 

However, Cuvier's theory of extinction is still justified in the case of mass extinctions that occurred in the last 600 million years, when approximately half of all living species went completely extinct within a short geological span of two million years, due in part by volcanic eruptions, asteroids, and rapid fluctuations in sea level. At this time, new species rose and others fell, precipitating the arrival of human beings. 

Cuvier's early work demonstrated conclusively that extinction was indeed a credible natural global process. Cuvier's thinking on extinctions was influenced by his extensive readings in Greek and Latin literature; he gathered every ancient report known in his day relating to discoveries of petrified bones of remarkable size in the Mediterranean region.

Influence on Cuvier's theory of extinction was his collection of specimens from the New World, many of them obtained from Native Americans. He also maintained an archive of Native American observations, legends, and interpretations of immense fossilized skeletal remains, sent to him by informants and friends in the Americas. He was impressed that most of the Native American accounts identified the enormous bones, teeth, and tusks as animals of the deep past that had been destroyed by catastrophe.

Catastrophism

These Indian elephant and mammoth jaws were included in 1799 when Cuvier's 1796 paper on living and fossil elephants was printed.

Cuvier came to believe that most, if not all, the animal fossils he examined were remains of species that had become extinct. Near the end of his 1796 paper on living and fossil elephants, he said:
All of these facts, consistent among themselves, and not opposed by any report, seem to me to prove the existence of a world previous to ours, destroyed by some kind of catastrophe.
Contrary to many natural scientists' beliefs at the time, Cuvier believed that animal extinction was not a product of anthropogenic causes. Instead, he proposed that humans were around long enough to indirectly maintain the fossilized records of ancient Earth. He also attempted to verify the water catastrophe by analyzing records of various cultural backgrounds. Though he found many accounts of the water catastrophe unclear, he did believe that such an event occurred at the brink of human history nonetheless. 

This led Cuvier to become an active proponent of the geological school of thought called catastrophism, which maintained that many of the geological features of the earth and the history of life could be explained by catastrophic events that had caused the extinction of many species of animals. Over the course of his career, Cuvier came to believe there had not been a single catastrophe, but several, resulting in a succession of different faunas. He wrote about these ideas many times, in particular he discussed them in great detail in the preliminary discourse (an introduction) to a collection of his papers, Recherches sur les ossements fossiles de quadrupèdes (Researches on quadruped fossil bones), on quadruped fossils published in 1812. 

Cuvier's own explanation for such a catastrophic event is derived from two different sources, including those from Jean-André Deluc and Déodat de Dolomieu. The former proposed that the continents existing ten millennia ago collapsed, allowing the ocean floors to rise higher than the continental plates and become the continents that now exist today. The latter proposed that a massive tsunami hit the globe, leading to mass extinction. Whatever the case was, he believed that the deluge happened quite recently in human history. In fact, he believed that Earth's existence was limited and not as extended as many natural scientists, like Lamarck, believed it to be. 

Much of the evidence he used to support his catastrophist theories have been taken from his fossil records. He strongly suggested that the fossils he found were evidence of the world's first reptiles, followed chronologically by mammals and humans. Cuvier didn't wish to delve much into the causation of all the extinction and introduction of new animal species but rather focused on the sequential aspects of animal history on Earth. In a way, his chronological dating of Earth history somewhat reflected Lamarck's transformationist theories. 

Cuvier also worked alongside Alexandre Brongniart in analyzing the Parisian rock cycle. Using stratigraphical methods, they were both able to extrapolate key information regarding Earth history from studying these rocks. These rocks contained remnants of molluscs, bones of mammals, and shells. From these findings, Cuvier and Brongniart concluded that many environmental changes occurred in quick catastrophes, though Earth itself was often placid for extended periods of time in between sudden disturbances. 

The 'Preliminary Discourse' became very well known and, unauthorized translations were made into English, German, and Italian (and in the case of those in English, not entirely accurately). In 1826, Cuvier would publish a revised version under the name, Discours sur les révolutions de la surface du globe (Discourse on the upheavals of the surface of the globe).

After Cuvier's death, the catastrophic school of geological thought lost ground to uniformitarianism, as championed by Charles Lyell and others, which claimed that the geological features of the earth were best explained by currently observable forces, such as erosion and volcanism, acting gradually over an extended period of time. The increasing interest in the topic of mass extinction starting in the late twentieth century, however, has led to a resurgence of interest among historians of science and other scholars in this aspect of Cuvier's work.

Stratigraphy

Cuvier collaborated for several years with Alexandre Brongniart, an instructor at the Paris mining school, to produce a monograph on the geology of the region around Paris. They published a preliminary version in 1808 and the final version was published in 1811.

In this monograph they identified characteristic fossils of different rock layers that they used to analyze the geological column, the ordered layers of sedimentary rock, of the Paris basin. They concluded that the layers had been laid down over an extended period during which there clearly had been faunal succession and that the area had been submerged under sea water at times and at other times under fresh water. Along with William Smith's work during the same period on a geological map of England, which also used characteristic fossils and the principle of faunal succession to correlate layers of sedimentary rock, the monograph helped establish the scientific discipline of stratigraphy. It was a major development in the history of paleontology and the history of geology.

Age of reptiles

In 1800 and working only from a drawing, Cuvier was the first to correctly identify in print, a fossil found in Bavaria as a small flying reptile, which he named the Ptero-Dactyle in 1809, (later Latinized as Pterodactylus antiquus)—the first known member of the diverse order of pterosaurs. In 1808 Cuvier identified a fossil found in Maastricht as a giant marine lizard, the first known mosasaur

Cuvier speculated correctly that there had been a time when reptiles rather than mammals had been the dominant fauna. This speculation was confirmed over the two decades following his death by a series of spectacular finds, mostly by English geologists and fossil collectors such as Mary Anning, William Conybeare, William Buckland, and Gideon Mantell, who found and described the first ichthyosaurs, plesiosaurs, and dinosaurs.

Principle of the correlation of parts

In a 1798 paper on the fossil remains of an animal found in some plaster quarries near Paris, Cuvier states what is known as the principle of the correlation of parts. He writes:
...if an animal's teeth are such as they must be, in order for it to nourish itself with flesh, we can be sure without further examination that the whole system of its digestive organs is appropriate for that kind of food, and that its whole skeleton and locomotive organs, and even its sense organs, are arranged in such a way as to make it skillful at pursuing and catching its prey. For these relations are the necessary conditions of existence of the animal; if things were not so, it would not be able to subsist.
This idea is referred to as Cuvier's principle of correlation of parts, which states that all organs in an animal's body are deeply interdependent. Species' existence relies on the way in which these organs interact. For example, a species whose digestive tract is best suited to digesting flesh but whose body is best suited to foraging for plants cannot survive. Thus in all species, the functional significance of each body part must be correlated to the others, else the species cannot sustain itself.

Applications

Cuvier believed that the power of his principle came in part from its ability to aid in the reconstruction of fossils. In most cases, fossils of quadrupeds were not found as complete, assembled skeletons, but rather as scattered pieces that needed to be put together by anatomists. To make matters worse, deposits often contained the fossilized remains of several species of animals mixed together. Anatomists reassembling these skeletons ran the risk of combining remains of different species, producing imaginary composite species. However, by examining the functional purpose of each bone and applying the principle of correlation of parts, Cuvier believed that this problem could be avoided.
This principle's ability to aid in reconstruction of fossils was also helpful to Cuvier's work in providing evidence in favor extinction. The strongest evidence Cuvier could provide in favor of extinction would be to prove that the fossilized remains of an animal belonged to a species that no longer existed. By applying Cuvier's principle of correlation of parts, it would be easier to verify that a fossilized skeleton had been authentically reconstructed, thus validating any observations drawn from comparing it to skeletons of existing species.

In addition to helping anatomists reconstruct fossilized remains, Cuvier believed that his principle held enormous predictive power as well. For example, when he discovered a fossil that resembled a marsupial in the gypsum quarries of Montmartre, he correctly predicted that the fossil would contain bones commonly found in marsupials in its pelvis as well.

Impact

Cuvier hoped that his principles of anatomy would provide the law-based framework that would elevate natural history to the truly scientific level occupied by physics and chemistry thanks to the laws established by Isaac Newton (1643 - 1727) and Antoine Lavoisier (1743 - 1794), respectively. He expressed confidence in the introduction to Le Règne Animal that some day anatomy would be expressed as laws as simple, mathematical, and predictive as Newton's laws of physics, and he viewed his principle as an important step in that direction. To him, the predictive capabilities of his principles demonstrated in his prediction of the existence of marsupial pelvic bones in the gypsum quarries of Montmartre demonstrated that these goals were not only in reach, but imminent.

The principle of correlation of parts was also Cuvier's way of understanding function in a non-evolutionary context, without invoking a divine creator. In the same 1798 paper on the fossil remains of an animal found in plaster quarries near Paris, Cuvier emphasizes the predictive power of his principle, writing:
Today comparative anatomy has reached such a point of perfection that, after inspecting a single bone, one can often determine the class, and sometimes even the genus of the animal to which it belonged, above all if that bone belonged to the head or the limbs ... This is because the number, direction, and shape of the bones that compose each part of an animal's body are always in a necessary relation to all the other parts, in such a way that—up to a point—one can infer the whole from any one of them and vice versa.
Though Cuvier believed that his principle's major contribution was that it was a rational, mathematical way to reconstruct fossils and make predictions, in reality it was difficult for Cuvier to use his principle. The functional significance of many body parts were still unknown at the time, and so relating those body parts to other body parts using Cuvier's principle was impossible. Though Cuvier was able to make accurate predictions about fossil finds, in practice the accuracy of his predictions came not from application of his principle, but rather from his vast knowledge of comparative anatomy. However, despite Cuvier's exaggerations of the power of his principle, the basic concept is central to comparative anatomy and paleontology.

Scientific work

Comparative anatomy and classification

At the Paris Museum, Cuvier furthered his studies on the anatomical classification of animals. He believed that classification should be based on how organs collectively function, a concept he called functional integration. Cuvier also reinforced the idea of subordinating less vital body parts to more critical organ systems as part of anatomical classification. He published these ideas in his book called Animal distribué d'après son organisation, pour servir de base à l'histoire naturelle des animaux et d'introduction à l'anatomie comparée, or The Animal Kingdom Arranged after its Organization; Forming a Natural History of Animals, and an Introduction to Comparative Anatomy) in 1817. 

In his anatomical studies, Cuvier believed function played a bigger role than form in the field of taxonomy. His scientific beliefs rested in the idea of the principles of the correlation of parts and of the conditions of existence. The former principle accounts for the connection between organ function and its practical use for an organism to survive. The latter principle emphasizes the animal's physiological function in relation to its surrounding environment. These findings were published in his scientific readings, including Leçons d'anatomie comparée (Lessons on Comparative Anatomy) and in Le Règne Animal (The Animal Kingdom) in the early 19th century and 1817 respectively.

Ultimately, Cuvier developed four embranchements, or branches, through which he classified animals based on his taxonomical and anatomical studies. He later performed groundbreaking work in classifying animals in vertebrate and invertebrate groups by subdividing each category. For instance, he proposed that the invertebrates could be segmented into three individual categories, including Mollusca, Radiata, and Articulata. He also articulated that species cannot move across these categories, a theory called transmutation. He reasoned that organisms cannot acquire or change their physical traits over time and still retain optimal survival. As a result, he often conflicted with Geoffroy Saint-Hilaire and Jean-Baptiste Lamarck's theories of transmutation. 

In 1798 Cuvier published his first independent work, the Tableau élémentaire de l'histoire naturelle des animaux, which was an abridgment of his course of lectures at the École du Pantheon and may be regarded as the foundation and first statement of his natural classification of the animal kingdom.

In 1800 he published the Leçons d'anatomie comparée, assisted by A. M. C. Duméril for the first two volumes and Georges Louis Duvernoy for the three later ones.

Molluscs

Cuvier categorized snails, cockles, and cuttlefish into one category he called molluscs, or mollusca, an embranchment. Though he noted how all three of these animals were outwardly different in terms of shell shape and diet, he saw a noticeable pattern pertaining to their overall physical appearance.

Cuvier began his intensive studies of molluscs during his time in Normandy—the first time he had ever seen the sea—and his papers on the so-called Mollusca began appearing as early as 1792. However, most of his memoirs on this branch were published in the Annales du museum between 1802 and 1815; they were subsequently collected as Mémoires pour servir à l'histoire et à l'anatomie des mollusques, published in one volume at Paris in 1817. 

"When the French Academy was preparing its first dictionary, it defined "crab" as, "A small red fish which walks backwards." This definition was sent with a number of others to the naturalist Cuvier for his approval. The scientist wrote back, "Your definition, gentlemen, would be perfect, only for three exceptions. The crab is not a fish, it is not red and it does not walk backwards."
Source unknown, but probably Times Literary Supplement (UK).

Fish

Cuvier's researches on fish, begun in 1801, finally culminated in the publication of the Histoire naturelle des poissons, which contained descriptions of 5,000 species of fishes, and was a joint production with Achille Valenciennes. Cuvier's work on this project extended over the years 1828–1831.

Palaeontology and osteology

Plate from Le Règne Animal, 1828 edition
 
In palaeontology, Cuvier published a long list of memoirs, partly relating to the bones of extinct animals, and partly detailing the results of observations on the skeletons of living animals, specially examined with a view toward throwing light upon the structure and affinities of the fossil forms. 

Among living forms he published papers relating to the osteology of the Rhinoceros Indicus, the tapir, Hyrax capensis, the hippopotamus, the sloths, the manatee, etc. 

He produced an even larger body of work on fossils, dealing with the extinct mammals of the Eocene beds of Montmartre, the fossil species of hippopotamus, a marsupial (which he called Didelphys gypsorum), the Megalonyx, the Megatherium, the cave-hyena, the pterodactyl, the extinct species of rhinoceros, the cave bear, the mastodon, the extinct species of elephant, fossil species of manatee and seals, fossil forms of crocodilians, chelonians, fish, birds, etc. If his identification of fossil animals was dependent upon comparison with the osteology of extant animals whose anatomy was poorly known, Cuvier would often publish a thorough documentation of the relevant extant species' anatomy before publishing his analyses of the fossil specimens. The department of palaeontology dealing with the Mammalia may be said to have been essentially created and established by Cuvier. 

The results of Cuvier's principal palaeontological and geological investigations ultimately were given to the world in the form of two separate works: Recherches sur les ossemens fossiles de quadrupèdes (Paris, 1812; later editions in 1821 and 1825); and Discours sur les revolutions de la surface du globe (Paris, 1825). In this latter work he expounded a scientific theory of Catastrophism.

The Animal Kingdom (Le Règne Animal)

Plate from Le Règne Animal, 1828 edition
 
Cuvier's most admired work was his Le Règne Animal. It appeared in four octavo volumes in 1817; a second edition in five volumes was brought out in 1829–1830. In this classic work, Cuvier presented the results of his life's research into the structure of living and fossil animals. With the exception of the section on insects, in which he was assisted by his friend Latreille, the whole of the work was his own. It was translated into English many times, often with substantial notes and supplementary material updating the book in accordance with the expansion of knowledge.

Racial studies

Cuvier was a Protestant and a believer in monogenism, who held that all men descended from the biblical Adam, although his position usually was confused as polygenist. Some writers who have studied his racial work have dubbed his position as "quasi-polygenist", and most of his racial studies have influenced scientific racism. Cuvier believed there were three distinct races: the Caucasian (white), Mongolian (yellow), and the Ethiopian (black). Cuvier claimed that Adam and Eve were Caucasian, the original race of mankind. The other two races originated by survivors escaping in different directions after a major catastrophe hit the earth 5,000 years ago, with those survivors then living in complete isolation from each other.

Cuvier categorized these divisions he identified into races according to his perception of the beauty or ugliness of their skulls and the quality of their civilizations. Cuvier's racial studies held the supposed features of polygenism, namely fixity of species; limits on environmental influence; unchanging underlying type; anatomical and cranial measurement differences in races; physical and mental differences between distinct races.

Official and public work

Engraving by James Thomson
 
Apart from his own original investigations in zoology and paleontology Cuvier carried out a vast amount of work as perpetual secretary of the National Institute, and as an official connected with public education generally; and much of this work appeared ultimately in a published form. Thus, in 1808 he was placed by Napoleon upon the council of the Imperial University, and in this capacity he presided (in the years 1809, 1811, and 1813) over commissions charged to examine the state of the higher educational establishments in the districts beyond the Alps and the Rhine that had been annexed to France, and to report upon the means by which these could be affiliated with the central university. He published three separate reports on this subject. 

In his capacity, again, of perpetual secretary of the Institute, he not only prepared a number of éloges historiques on deceased members of the Academy of Sciences, but was also the author of a number of reports on the history of the physical and natural sciences, the most important of these being the Rapport historique sur le progrès des sciences physiques depuis 1789, published in 1810. 

Prior to the fall of Napoleon (1814) he had been admitted to the council of state, and his position remained unaffected by the restoration of the Bourbons. He was elected chancellor of the university, in which capacity he acted as interim president of the council of public instruction, whilst he also, as a Lutheran, superintended the faculty of Protestant theology. In 1819 he was appointed president of the committee of the interior, an office he retained until his death. 

In 1826 he was made grand officer of the Legion of Honour; he subsequently was appointed president of the council of state. He served as a member of the Académie des Inscriptions et Belles-Lettres from 1830 to his death. A member of the Doctrinaires, he was nominated to the ministry of the interior in the beginning of 1832.

Commemorations

Statue of Cuvier by David d'Angers, 1838
 
Cuvier is commemorated in the naming of several animals; they include Cuvier's beaked whale (which he first thought to be extinct), Cuvier's gazelle, Cuvier's toucan, Cuvier's bichir, Cuvier's dwarf caiman, and Galeocerdo cuvier (tiger shark). Cuvier is commemorated in the scientific name of the following reptiles: Anolis cuvieri (a lizard from Puerto Rico), Bachia cuvieri, and Oplurus cuvieri. There also are some extinct animals named after Cuvier, such as the South American giant sloth Catonyx cuvieri

Cuvier Island in New Zealand was named after Cuvier by D'Urville.

The professor of English Wayne Glausser argues at length that the Aubrey-Maturin series of 21 novels (1970–2004) by Patrick O'Brian make the character Stephen Maturin "an advocate of the neo-classical paradigm articulated .. by Georges Cuvier."

Cuvier is referenced in Edgar Allan Poe's short story The Murders in the Rue Morgue as having written a description of the orangutan.

Works

--- Essay on the theory of the earth, 1813; 1815, trans. Robert Kerr.
  • Recherches sur les ossemens fossiles, 1821–1823 (5 vols).
  • Discours sur les révolutions de la surface du globe et sur les changements qu'elles ont produits dans le règne animal (1822). New edition: Christian Bourgeois, Paris, 1985. (text in French)
  • Histoire des progrès des sciences naturelles depuis 1789 jusqu'à ce jour (5 volumes, 1826–1836)
  • Histoire naturelle des poissons (11 volumes, 1828–1848), continued by Achille Valenciennes
  • Histoire des sciences naturelles depuis leur origine jusqu'à nos jours, chez tous les peuples connus, professée au Collège de France (5 volumes, 1841–1845), edited, annotated, and published by Magdeleine de Saint-Agit
  • Cuvier's History of the Natural Sciences: twenty-four lessons from Antiquity to the Renaissance [edited and annotated by Theodore W. Pietsch, translated by Abby S. Simpson, foreword by Philippe Taquet], Paris: Publications scientifiques du Muséum national d'Histoire naturelle, 2012, 734 p. (coll. Archives; 16) ISBN 978-2-85653-684-1
Cuvier also collaborated on the Dictionnaire des sciences naturelles (61 volumes, 1816–1845) and on the Biographie universelle (45 volumes, 1843-18??)

Post-glacial rebound

From Wikipedia, the free encyclopedia

A model of present-day mass change due to post-glacial rebound and the reloading of the ocean basins with seawater. Blue and purple areas indicate rising due to the removal of the ice sheets. Yellow and red areas indicate falling as mantle material moved away from these areas in order to supply the rising areas, and because of the collapse of the forebulges around the ice sheets.
This layered beach at Bathurst Inlet, Nunavut is an example of post-glacial rebound after the last Ice Age. Little to no tide helped to form its layer-cake look. Isostatic rebound is still underway here.
Post-glacial rebound (also called isostatic rebound or crustal rebound) is the rise of land masses after the lifting of the huge weight of ice sheets during the last glacial period, which had caused isostatic depression. Post-glacial rebound and isostatic depression are phases of glacial isostasy (glacial isostatic adjustment, glacioisostasy), the deformation of the Earth's crust in response to changes in ice mass distribution. The direct raising effects of post-glacial rebound are readily apparent in parts of Northern Eurasia, Northern America, Patagonia, and Antarctica. However, through the processes of ocean siphoning and continental levering, the effects of post-glacial rebound on sea level are felt globally far from the locations of current and former ice sheets.

Overview

Changes in the elevation of Lake Superior due to glaciation and post-glacial rebound
During the last glacial period, much of northern Europe, Asia, North America, Greenland and Antarctica was covered by ice sheets, which reached up to three kilometres thick during the glacial maximum about 20,000 years ago. The enormous weight of this ice caused the surface of the Earth's crust to deform and warp downward, forcing the viscoelastic mantle material to flow away from the loaded region. At the end of each glacial period when the glaciers retreated, the removal of this weight led to slow (and still ongoing) uplift or rebound of the land and the return flow of mantle material back under the deglaciated area. Due to the extreme viscosity of the mantle, it will take many thousands of years for the land to reach an equilibrium level.
The uplift has taken place in two distinct stages. The initial uplift following deglaciation was almost immediate due to the elastic response of the crust as the ice load was removed. After this elastic phase, uplift proceeded by slow viscous flow at an exponentially decreasing rate. Today, typical uplift rates are of the order of 1 cm/year or less. In northern Europe, this is clearly shown by the GPS data obtained by the BIFROST GPS network. Studies suggest that rebound will continue for at least another 10,000 years. The total uplift from the end of deglaciation depends on the local ice load and could be several hundred metres near the centre of rebound.
Recently, the term "post-glacial rebound" is gradually being replaced by the term "glacial isostatic adjustment". This is in recognition that the response of the Earth to glacial loading and unloading is not limited to the upward rebound movement, but also involves downward land movement, horizontal crustal motion, changes in global sea levels and the Earth's gravity field, induced earthquakes, and changes in the Earth's rotation. Another alternate term is "glacial isostasy", because the uplift near the centre of rebound is due to the tendency towards the restoration of isostatic equilibrium (as in the case of isostasy of mountains). Unfortunately, that term gives the wrong impression that isostatic equilibrium is somehow reached, so by appending "adjustment" at the end, the motion of restoration is emphasized.

Effects

Post-glacial rebound produces measurable effects on vertical crustal motion, global sea levels, horizontal crustal motion, gravity field, Earth's rotation, crustal stress, and earthquakes. Studies of glacial rebound give us information about the flow law of mantle rocks, which is important to the study of mantle convection, plate tectonics and the thermal evolution of the Earth. It also gives insight into past ice sheet history, which is important to glaciology, paleoclimate, and changes in global sea level. Understanding postglacial rebound is also important to our ability to monitor recent global change.

Vertical crustal motion

Much of modern Finland is former seabed or archipelago: illustrated are sea levels immediately after the last ice age.
Erratic boulders, U-shaped valleys, drumlins, eskers, kettle lakes, bedrock striations are among the common signatures of the Ice Age. In addition, post-glacial rebound has caused numerous significant changes to coastlines and landscapes over the last several thousand years, and the effects continue to be significant.
In Sweden, Lake Mälaren was formerly an arm of the Baltic Sea, but uplift eventually cut it off and led to its becoming a freshwater lake in about the 12th century, at the time when Stockholm was founded at its outlet. Marine seashells found in Lake Ontario sediments imply a similar event in prehistoric times. Other pronounced effects can be seen on the island of Öland, Sweden, which has little topographic relief due to the presence of the very level Stora Alvaret. The rising land has caused the Iron Age settlement area to recede from the Baltic Sea, making the present day villages on the west coast set back unexpectedly far from the shore. These effects are quite dramatic at the village of Alby, for example, where the Iron Age inhabitants were known to subsist on substantial coastal fishing.
As a result of post-glacial rebound, the Gulf of Bothnia is predicted to eventually close up at Kvarken in more than 2,000 years. The Kvarken is a UNESCO World Natural Heritage Site, selected as a "type area" illustrating the effects of post-glacial rebound and the holocene glacial retreat.
In several other Nordic ports, like Tornio and Pori (formerly at Ulvila), the harbour has had to be relocated several times. Place names in the coastal regions also illustrate the rising land: there are inland places named 'island', 'skerry', 'rock', 'point' and 'sound'. For example, Oulunsalo "island of Oulujoki" is a peninsula, with inland names such as Koivukari "Birch Rock", Santaniemi "Sandy Cape", and Salmioja "the brook of the Sound".
Map of Post Glacial Rebound effects upon the land-level on the British Isles.
In Great Britain, glaciation affected Scotland but not southern England, and the post-glacial rebound of northern Great Britain (up to 10 cm per century) is causing a corresponding downward movement of the southern half of the island (up to 5 cm per century). This will eventually lead to an increased risk of floods in southern England and south-western Ireland.
Since the glacial isostatic adjustment process causes the land to move relative to the sea, ancient shorelines are found to lie above present day sea level in areas that were once glaciated. On the other hand, places in the peripheral bulge area which was uplifted during glaciation now begins to subside. Therefore, ancient beaches are found below present day sea level in the bulge area. The "relative sea level data", which consists of height and age measurements of the ancient beaches around the world, tells us that glacial isostatic adjustment proceeded at a higher rate near the end of deglaciation than today.
The present-day uplift motion in northern Europe is also monitored by a GPS network called BIFROST. Results of GPS data show a peak rate of about 11 mm/year in the north part of the Gulf of Bothnia, but this uplift rate decreases away and becomes negative outside the former ice margin.
In the near field outside the former ice margin, the land sinks relative to the sea. This is the case along the east coast of the United States, where ancient beaches are found submerged below present day sea level and Florida is expected to be submerged in the future. GPS data in North America also confirms that land uplift becomes subsidence outside the former ice margin.

Global sea levels

To form the ice sheets of the last Ice Age, water from the oceans evaporated, condensed as snow and was deposited as ice in high latitudes. Thus global sea level fell during glaciation.
The ice sheets at the last glacial maximum were so massive that global sea level fell by about 120 metres. Thus continental shelves were exposed and many islands became connected with the continents through dry land. This was the case between the British Isles and Europe (Doggerland), or between Taiwan, the Indonesian islands and Asia (Sundaland). A sub-continent also existed between Siberia and Alaska that allowed the migration of people and animals during the last glacial maximum.
The fall in sea level also affects the circulation of ocean currents and thus has important impact on climate during the glacial maximum.
During deglaciation, the melted ice water returns to the oceans, thus sea level in the ocean increases again. However, geological records of sea level changes show that the redistribution of the melted ice water is not the same everywhere in the oceans. In other words, depending upon the location, the rise in sea level at a certain site may be more than that at another site. This is due to the gravitational attraction between the mass of the melted water and the other masses, such as remaining ice sheets, glaciers, water masses and mantle rocks and the changes in centrifugal potential due to Earth's variable rotation.

Horizontal crustal motion

Accompanying vertical motion is the horizontal motion of the crust. The BIFROST GPS network shows that the motion diverges from the centre of rebound. However, the largest horizontal velocity is found near the former ice margin.
The situation in North America is less certain; this is due to the sparse distribution of GPS stations in northern Canada, which is rather inaccessible.

Post-glacial rebound and isostasy

Vertical motion of a crustal block means that this block is not in isostatic equilibrium. However, it is in the process of reaching this equilibrioum.

Tilt

The combination of horizontal and vertical motion changes the tilt of the surface. That is, locations farther north rise faster, an effect that becomes apparent in lakes. The bottoms of the lakes gradually tilt away from the direction of the former ice maximum, such that lake shores on the side of the maximum (typically north) recede and the opposite (southern) shores sink. This causes the formation of new rapids and rivers. For example, Lake Pielinen, which is large (90 x 30 km) and oriented perpendicularly to the former ice margin, originally drained through an outlet in the middle of the lake near Nunnanlahti to Lake Höytiäinen. The change of tilt caused Pielinen to burst through the Uimaharju esker at the southwestern end of the lake, creating a new river (Pielisjoki) that runs to the sea via Lake Pyhäselkä to Lake Saimaa. The effects are similar to that concerning seashores, but occur above sea level. Tilting of land will also affect the flow of water in lakes and rivers in the future, and thus important for water resource management planning.

Gravity field

Ice, water and mantle rocks have mass, and as they move around, they exert a gravitational pull on other masses towards them. Thus, the gravity field, which is sensitive to all mass on the surface and within the Earth, is affected by the redistribution of ice/melted water on the surface of the Earth and the flow of mantle rocks within.
Today, more than 6000 years after the last deglaciation terminated, the flow of mantle material back to the glaciated area causes the overall shape of the Earth to become less oblate. This change in the topography of Earth's surface affects the long-wavelength components of the gravity field.
The changing gravity field can be detected by repeated land measurements with absolute gravimeters and recently by the GRACE satellite mission. The change in long-wavelength components of Earth's gravity field also perturbs the orbital motion of satellites and has been detected by LAGEOS satellite motion.

Vertical datum

The vertical datum is a theoretical reference surface for altitude measurement and plays vital roles in many human activities, including land surveying and construction of buildings and bridges. Since postglacial rebound continuously deforms the crustal surface and the gravitational field, the vertical datum needs to be redefined repeatedly through time.

State of stress, intraplate earthquakes and volcanism

According to the theory of plate tectonics, plate-plate interaction results in earthquakes near plate boundaries. However, large earthquakes are found in intraplate environment like eastern Canada (up to M7) and northern Europe (up to M5) which are far away from present-day plate boundaries. An important intraplate earthquake was the magnitude 8 New Madrid earthquake that occurred in mid-continental US in the year 1811.
Glacial loads provided more than 30 MPa of vertical stress in northern Canada and more than 20 MPa in northern Europe during glacial maximum. This vertical stress is supported by the mantle and the flexure of the lithosphere. Since the mantle and the lithosphere continuously respond to the changing ice and water loads, the state of stress at any location continuously changes in time. The changes in the orientation of the state of stress is recorded in the postglacial faults in southeastern Canada. When the postglacial faults formed at the end of deglaciation 9000 years ago, the horizontal principal stress orientation was almost perpendicular to the former ice margin, but today the orientation is in the northeast-southwest, along the direction of seafloor spreading at the Mid-Atlantic Ridge. This shows that the stress due to postglacial rebound had played an important role at deglacial time, but has gradually relaxed so that tectonic stress has become more dominant today.
According to the Mohr–Coulomb theory of rock failure, large glacial loads generally suppress earthquakes, but rapid deglaciation promotes earthquakes. According to Wu & Hasagawa, the rebound stress that is available to trigger earthquakes today is of the order of 1 MPa. This stress level is not large enough to rupture intact rocks but is large enough to reactivate pre-existing faults that are close to failure. Thus, both postglacial rebound and past tectonics play important roles in today's intraplate earthquakes in eastern Canada and southeast US. Generally postglacial rebound stress could have triggered the intraplate earthquakes in eastern Canada and may have played some role in triggering earthquakes in the eastern US including the New Madrid earthquakes of 1811. The situation in northern Europe today is complicated by the current tectonic activities nearby and by coastal loading and weakening.
Increasing pressure due to the weight of the ice during glaciation may have suppressed melt generation and volcanic activities below Iceland and Greenland. On the other hand, decreasing pressure due to deglaciation can increase the melt production and volcanic activities by 20-30 times.

Recent global warming

Recent global warming has caused mountain glaciers and the ice sheets in Greenland and Antarctica to melt and global sea level to rise. Therefore, monitoring sea level rise and the mass balance of ice sheets and glaciers allows people to understand more about global warming.
Recent rise in sea levels has been monitored by tide gauges and satellite altimetry (e.g. TOPEX/Poseidon). As well as the addition of melted ice water from glaciers and ice sheets, recent sea level changes are affected by the thermal expansion of sea water due to global warming, sea level change due to deglaciation of the last glacial maximum (postglacial sea level change), deformation of the land and ocean floor and other factors. Thus, to understand global warming from sea level change, one must be able to separate all these factors, especially postglacial rebound, since it is one of the leading factors.
Mass changes of ice sheets can be monitored by measuring changes in the ice surface height, the deformation of the ground below and the changes in the gravity field over the ice sheet. Thus ICESat, GPS and GRACE satellite mission are useful for such purpose. However, glacial isostatic adjustment of the ice sheets affect ground deformation and the gravity field today. Thus understanding glacial isostatic adjustment is important in monitoring recent global warming.
One of the possible impacts of global warming-triggered rebound may be more volcanic activity in previously ice-capped areas such as Iceland and Greenland. It may also trigger intraplate earthquakes near the ice margins of Greenland and Antarctica.

Applications

The speed and amount of postglacial rebound is determined by two factors: the viscosity or rheology (i.e., the flow) of the mantle, and the ice loading and unloading histories on the surface of Earth.
The viscosity of the mantle is important in understanding mantle convection, plate tectonics, dynamical processes in Earth, the thermal state and thermal evolution of Earth. However viscosity is difficult to observe because creep experiments of mantle rocks take thousands of years to observe and the ambient temperature and pressure conditions are not easy to attain for a long enough time. Thus, the observations of postglacial rebound provide a natural experiment to measure mantle rheology. Modelling of glacial isostatic adjustment addresses the question of how viscosity changes in the radial and lateral directions and whether the flow law is linear, nonlinear, or composite rheology.
Ice thickness histories are useful in the study of paleoclimatology, glaciology and paleo-oceanography. Ice thickness histories are traditionally deduced from the three types of information: First, the sea level data at stable sites far away from the centers of deglaciation give an estimate of how much water entered the oceans or equivalently how much ice was locked up at glacial maximum. Secondly, the location and dates of terminal moraines tell us the areal extent and retreat of past ice sheets. Physics of glaciers gives us the theoretical profile of ice sheets at equilibrium, it also says that the thickness and horizontal extent of equilibrium ice sheets are closely related to the basal condition of the ice sheets. Thus the volume of ice locked up is proportional to their instantaneous area. Finally, the heights of ancient beaches in the sea level data and observed land uplift rates (e.g. from GPS or VLBI) can be used to constrain local ice thickness. A popular ice model deduced this way is the ICE5G model. Because the response of the Earth to changes in ice height is slow, it cannot record rapid fluctuation or surges of ice sheets, thus the ice sheet profiles deduced this way only gives the "average height" over a thousand years or so.
Glacial isostatic adjustment also plays an important role in understanding recent global warming and climate change.

Discovery

Before the eighteenth century, it was thought, in Sweden, that sea levels were falling. On the initiative of Anders Celsius a number of marks were made in rock on different locations along the Swedish coast. In 1765 it was possible to conclude that it was not a lowering of sea levels but an uneven rise of land. In 1865 Thomas Jamieson came up with a theory that the rise of land was connected with the ice age that had been first discovered in 1837. The theory was accepted after investigations by Gerard De Geer of old shorelines in Scandinavia published in 1890.

Legal implications

In areas where the rising of land is seen, it is necessary to define the exact limits of property. In Finland, the "new land" is legally the property of the owner of the water area, not any land owners on the shore. Therefore, if the owner of the land wishes to build a pier over the "new land", they need the permission of the owner of the (former) water area. The landowner of the shore may redeem the new land at market price. Usually the owner of the water area is the partition unit of the landowners of the shores, a collective holding corporation.

Representation of a Lie group

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Representation_of_a_Lie_group...