History of geology

In contrast to the historical geology that deals with the history of the Earth, is the subject of the history of geology, the development of this science itself It overlaps with the history of other geosciences, such as mineralogy, petrography, and paleontology.

• 3.1 miners ...
• 3.2 ... and alchemists

• 5.1 A couple, like fire and water: plutonism and Neptunism
• 5.2 A current eternal world, or a universe of disasters?
• 5.3 The first global hypotheses on the formation of mountains
• 5.4 The search for the entrenched supercontinent
• 5.5 The discovery of the drifting continents
• 5.6 The change of working methods in the 20th century
• 5.7 Outlook and open questions

Antiquity

The origins of geology shall come from two very different sources: on the one hand, from the practical knowledge of the prospectors, miners and metallurgists, which supplied the ancient civilizations with the necessary raw materials, on the other hand, from the very first germs of Western philosophy.

Minerals, fossils and rocks in the Ionian natural philosophy

It was Thales of Miletus (c. 624 to 546 BC) to replace, the founder of the Ionian natural philosophy who has tried first, the ancient mythological ideas about the earth by rational explanations. No longer the rumbling, earth-shaker ' Poseidon he was responsible for causing the earthquake, but the movements of the floating on the primordial waters flat earth. Likewise, Thales seems to be reached at the edge of hot springs to his theory by observing the sedimentation at sandbars at the mouth of large rivers, or the precipitation of minerals, all things were created out of the water.

Anaximander (c. 610 to 546 BC), drew not only the first map of the inhabited world, but then expanded Thales ideas on the busy world. He taught that living beings are born from the moisture that Evaporate under the action of the sun. As a result, evolved from fish-like creatures, man. Of course it is pure chance that is being discussed again today whether the first building blocks of life ( " primordial soup " ) have formed in the sea, or whether they had focused more in hot, mineral- saturated water holes. Nevertheless, attacks Anaximander ' amazing thesis of modern evolutionary theory by more than 2400 years ahead. Finally, he considers the first thinker a natural process of development of living beings. In any case, it shows that it was the phenomenon of precipitation of sea salt by solar radiation ( evaporation) known.

Xenophanes of Colophon (c. 570 to 470 BC) suggested for the first time the imprints of shells and other marine animals in sea distant land lines as the remains of fossilized creatures ( fossils). Your position he explained so that the mountains would have lifted once from the sea. He also recognized the progressive erosion on the coasts. From these two processes he graduated to large cycles in which orogeny and erosion alternated. With the destruction of the continents will thereby be destroyed each time the particular mankind.

Metaphysical speculation in Greek philosophy

All this nature facing approaches were already in the 4th century BC again as outdated. The Greek philosophy devoted instead increasingly formal logical and transcendental problems. While the Pythagoreans in southern Italy transformed the mathematics in a secret mystery religion, the Sophists were limited to exercises in grammar, dialectic and rhetoric. The ideas about the formation of rocks and metals moving soon only in the realm of pure speculation, largely refrained from empirical observations. As for example, Anaxagoras of Klazomenai (around 500-428 BC) claimed that the rocky nature of the heavenly bodies had been proved by the fall of the meteorite of Aigospotamoi, earned him already a conviction for blasphemy one.

Plato ( 427-348 BC) linked the doctrine of the four elements of Empedocles with the mathematical speculations of the Pythagoreans on the geometrical shape of the atoms. The metals and minerals do not exist, therefore, as the stones and earth, of mixed elements, but especially from compacted fusible water ', pronounced especially hard frozen ice.

Aristotle ( 384-322 BC) advocated in his book Meteorologia the momentous doctrine of transformation ( transmutation) of the elements. The transformation he led to the deep penetration of the sun's rays back into the earth body. From the resulting dry vapors thus incur the rock and from the humid vapors, the metals. His idea about the formation of fossils inside rocks by an indefinite creative power (Latin: vis plastica ) should also keep well into the modern period validity. The rise and fall of the Earth's surface that cause stranding and ablation were known to him. In his opinion, they were based on the slow but irregular aging process of the earth.

The cause for the development and growth of all things, so also the minerals, was the logos (Greek: the word the sensible speech, the reasoning ), a general metaphysical principle of order that pervades the entire cosmos. In the philosophical school of Stoicism it was developed the concept of the Logoi spermaticoi, the " seed -like grounds". These included, so it was assumed the ideas that define the final shape of individual things. In Neo-Platonism, which should have a significant influence on Christian theology later, these ideas sprang from the divine spirit. Today we would here probably think of the atomic binding forces that compel the individual atoms of a mineral in a crystal lattice, or the genes that determine the development of a living organism.

The ancient " stone books"

Such views were summarized by Theophrastus, the disciple and successor of Aristotle, in his treatise On the stones. After that, they were, until well into the modern era, as generally binding. In the later stone books these theories but these were mixed with ideas from the East, on the magical- astrological and medicinal properties of metals and precious stones, but also with practical recipes for the counterfeiting of gold, as well as for the artificial production of glass and dyes. Here one may see the origins of technical chemistry.

The last great summary of all this, now very extensive and contradictory, material undertook Pliny the Elder in his Naturalis Historia encyclopedic, the last five books is concerned with the mineral kingdom. In the eruption of Mount Vesuvius which destroyed the city of Pompeii, Pliny ventured out to help, but also out of curiosity too close to the volcano zoom and choked on the exiting gases. Due to the very detailed eyewitness account of his nephew, Pliny the Younger such explosive eruptions are still called Plinian eruptions.

Otherwise, only a few geological observations were made in ancient times. The lack of interest was based on a v. of the general contempt of dirty hand. So there was especially the field of applied geology, such as mining and geology, the exclusive domain of slaves and artisans, who passed their practical knowledge in the best case orally. Only in the biblical book of Job (Job 28.1 to 19 EU ), there is a brief account on the ( ultimately unfulfilled ) desire to research the miners.

The Fundamentals of Christian Erdbildes

In the Christian late antiquity many old ideas about the nature of the world have already been lost. So already in Antioch ( 115-181 ) rejected Theophilus the ancient Greek ideas about the eternity of the world, or many thousands of years cycles of creation of Earth and Erdvernichtung. Instead, he tried, according to the Jewish role model to calculate the age of the earth from the statements of the Bible, where he came up with a date of 5529 BC. Lactantius Firmianus (ca. 240-320 ), however, denied the sphericity of the earth, and favored a flat -earth theory, as it was suggested by his reading of the Old Testament.

Middle Ages

While in Western Europe after the collapse of the Roman Empire began a long period of stagnation in the mining, ancient ideas about the origin of the ores and rocks were further developed in the Arab- Muslim culture. Ibn Sina ( Latinized: Avicenna, 980-1037 to ) handle this particular back to Aristotle, whose doctrine of the transformation of metals, however, he refused. In addition, he delivered a seemingly modern classification of the mineral kingdom in salts, sulfur, metals and stones. From the layered form of rocks, he joined on their formation by sedimentation, and the formation of mountains, he led back to the effects of earthquakes. In his ideas of the effect of water Ibn Sina was, incidentally close to a medal ( tariqa ) of Sufi mystics, the, Brethren of Purity ' called themselves. They taught that the oceans filled over long periods of time with sediments from the mountains and rivers. Finally, the seas flowed over and new material encamped on the mainlanders from.

Such ancient and Arab notions came in the 12th and 13th centuries in Western Europe, where they inspired the western alchemists. This explained the formation of the metals by the concentrated rays of all the planets at the center of the Earth, which was conceived of as a huge, fiery furnace. Albertus Magnus (1200-1280) described the formation of veins like a distillation process. The heat of the Earth, the finer elements of the moist exhalations are driven into the natural pores and cracks of the earth's crust. There they are, much like the neck of a retort, cooled, excreted and concentrated. This essentially corresponds to the modern theory of hydrothermal vein deposits.

Otherwise, the medieval man taught when he questions about the state of the world made ​​itself, his gaze to the sky rather than on the floor. Beneath his feet In heaven, he suspected, depending on the level of education, either one all-ruling God, or the forces of attraction and radiation of the planets up Hoeben the mountains, the seas were retreating, or the growth of minerals, plants and animals caused.

In the late Middle Ages came (especially through the inclusion of Aristotelian philosophy into Christian theology ) the first doubts on the short biblical chronology; so with Jean Buridan (ca. 1328-1358 ), the postulated an eternal world with cycles of " perhaps hundreds of thousands of millions of years ", even if it seemed incompatible with the Christian faith. The Reformation, with its programmatic return to the text of the Bible, but the Biblical chronology once again supported.

Renaissance

Leonardo da Vinci (1452-1519) discovered the organic nature of fossils again and described it in the Codex Leicester, which he denied the importance of the biblical deluge for the process clear. He also rejected the, calculated from the Bible, short age of the earth, and observed the different sedimentation of sand grains in flowing water. Since Leonardo 's notebooks but never published his findings remained virtually ineffective.

Miners ...

As the beginning of modern geology is therefore considered the work of Georgius Agricola ( 1494-1555 ). The main part of his De re metallica libri XII consists of detailed descriptions of the former mining and engineering, the construction of furnaces, manufacture of soda, saltpetre, sulfur and alum, transport of ores, wind and hydropower, but also legal and administrative concerns. In the first chapters he gives but also practical information about the discovery of deposits ( exploration ) on the basis of natural labels. His De natura Fossilium is considered the first manual of mineralogy, as the classification of minerals based on external characteristics, such as color, luster and taste. In his work De ortu et causis subterraneorum ( 1546) Agricola describes his views on the formation of minerals. Here he took the effect of a " petrifying juice " ( succus lapidescens ), which arises from the common heating and thickening of dry and moist substances in subterranean waters, and the surrounding rocks decomposed (literally licks ). In this concept, you can see an early predecessor of the " mineral - containing solutions " (fluids) in modern geology, although Agricola the many different mineral formations, attributed to the mere action of heat and cold on the model of Aristotle, but somewhat unsatisfactory. Agricola rejected not only the biblical theory that all minerals were formed at the moment of divine creation, but also the alchemical theory of the transformation of metals. Nevertheless, should keep this for a long time. An important drive for the European voyages of discovery overseas was, for example, the idea that there is the, sun metal ' gold especially in the hot, tropical regions of the world.

The Swiss naturalist Conrad Gesner (1516-1565) collected in his work De Rerum Fossilium, lapidum et gemmarum ( 1565), in the spirit of the ancient stone books, a plethora of (often incorrect ) information about fossils, minerals and gemstones.

And alchemists ...

Another example of the ( rather free ) harking back to the ancient tradition are the speculations of the humanist scholar Paracelsus ( 1493-1541 ) dar. In his opinion, the divine, immaterial spirit ( Iliaster ) had in the four elements of fire, water, air divided and the earth, each of which could serve as a matrix for the formation of different substances. The minerals were growing, therefore, on the basis of a metaphysical order principle ( archeus ) in the earth, much like plant seeds. Your matrix is the water that runs in a web of underground water through the whole earth system. He also divided, similar to the Christian Trinity, the nature in the property -imparting basic elements of salt, sulfur and mercury. Here, however, he reached back to Arab traditions rather than to Greek.

The notion of minerals as " seeds " that grow in the earth, until they eventually turn into "mature" metals, can be found not only in the way alchemists, but also in the folklore of the miners and metallurgists of many nations.

In the writings of the German alchemist and mining engineer Johann Joachim Becher (1635-1682) developed Paracelsus ' principles of salt, sulfur and mercury in the " glassy earth" ( the mother of the stones), the "rich world " (Mother of ordinary earth) and " mercurial earth" ( mother of the metals). While the mercurial earth disappeared in the later development of the theory soon the glassy earth was brought into contact with the mineral quartz compound which actually is a main component of the rocks, and often forms the matrix for other minerals. The rich earth turned into the theory in the phlogiston, a hypothetical substance that should make the things flammable. The transfer of phlogiston from a substance to another has been a long time for the explanation of combustion reactions and metallurgical processes drawn up who we would today call reduction and oxidation. During the 18th century developed from such concepts, the notions of special earths such as lime, silica, magnesia and alum, which came to be seen as a quasi- chemical constituents of minerals.

The discovery of the earth's

What the geology differs from most other sciences, is esp. the historical approach. The minerals could be classified easily by a chemist, the fossils of a biologist. The properties of the earth could describe a physicist, his figure a geographer. However, the geologist is not only the question: " What is it? " But most of all: " How was it, what is it?"

The first steps in the direction of Earth's history was the Danish physician and scientist Niels Stensen, Latinized: Nicolaus Steno ( 1638-1687 ). In 1669 he designed in Tuscany the first geological profile that was really meant historically. With the basic knowledge that the lower layers of rock are older, and the overlying about gradually getting younger, Stensen discovered the stratigraphic principle. The arrangement in space corresponds in reality to a sequence in time. In addition, Stensen postulated that all layers were originally deposited horizontally, and that the layers displaced by the Earth's interior forces only later, broken and can be folded. Likewise Stensen realized again the organic nature of fossils. Had the fossils formed only later within the rock, as Aristotle believed, then they would have been deformed by the surrounding rock, as tree roots that grow into a Erdspalt. In fact, however, the surrounding rock at the fossils fit in, so it was clear that they had to be older than the surrounding rock. As first recognized crystallographer Stensen on quartz, the law of constant angles.

Stensens contemporaries continued to use the problem why the fossils were deeply embedded in the rocks, rather than to lie on the surface. A way out was to simply deny the organic origin of fossils, and they dismiss it as spontaneous formations and curious " freaks of nature ", as, for example, Martin Lister (1638-1711) did. Robert Hooke (1638-1703) Inspiration, that one could reconstruct a chronology of changing environmental conditions from the fossil contents of the rocks, was initially not pursued.

Such geological approaches but were hampered by the adherence to the biblical time scale for a long time. The best known example is the calculation of the Archbishop of Armagh (Ireland), James Usher ( 1580-1656 ), who on Monday 23 October 4004 dated the creation of the world BC. As the only event that could have materially changed the face of the earth after the Creation, the Flood was. It was the sea made ​​not only for the existence of fossils remotely responsible, but also for the widespread Geschiebelehme. These occur in large areas of northern and central Europe rocks were detected only in the 19th century as evidence of the last ice age. Because of the similarity of the coastlines of Africa and South America, a theologian named Lilienthal made ​​responsible in 1736 for the Flood even the breakup of the continents.

The geology as a modern science

In the course of the Enlightenment faith went to the biblical time scale gradually lost and you tried to build a bridge between the traditional practical knowledge of the miners and metallurgists and purely theoretical speculations of Descartes, Leibniz and Kant on the origin of the earth. Thus, the geology took the change from a descriptive to an explanatory science. The collection of fossils and minerals was among the middle classes into a real fad, and knowledge of geological oddities were considered an important part of general education.

The first who were preparing Hooke's idea about a possible history of the earth to put into action, the Prussian mining engineer Johann Gottlob Lehmann (1719-1767) and the princely personal physician Georg Christian Füchsel were ( 1722-1773 ). However, they do attracted more the different design of the rocks ( lithology ) to rate than the fossil content. In the mid-18th century they made the first profile sections and geological maps, representing the layers of rock in the mining districts of Thuringia.

Also the Tuscan mine director Giovanni Arduino (1735-1795) produced a profile of the Italian Alpine foreland. He divided the rocks of the earth's crust, primary ',' secondary ', Tertiary and Quaternary. The last two term are still in use, the first two correspond approximately to the Paleozoic and Mesozoic today. He also realized that the fossils of the organisms living today are becoming increasingly similar in the younger layers.

However, the breakthrough in the basic working method of geological mapping succeeded the surveying engineer and canal builder William Smith ( 1769-1839 ). In 1815 he published his monumental, colorful map of the geology of England and Wales, which drew both the fossil content, as well as the lithology into consideration. Smith had thereby recognized that certain rock sequences are also characterized by a very specific, distinctive Faunenfolge. 1827 coined Leopold von Buch ( 1774-1853 ) for such fossils, which allowed a relative dating, the term index fossil. Smith's map was still pointing the way for all future projects of the national offices of the Länder. With the help of these cards, it is the geologist not only possible to represent the distribution of certain rocks on the surface, but also to predict its location in the underground. The more one is aware that it is also about temporal units in the strata, the more was the geological map to a complex representation of four dimensions ( three of space and time ) in two dimensions.

The development of geology took place below in a number of, sometimes extremely violent, scientific controversies.

A couple, like fire and water: plutonism and Neptunism

The first of these controversies was the so-called " basalt dispute" between Plutonists and Neptunists. Ostensibly done scientifically, was the basalt dispute also a fundamental discussion of different religious beliefs about the biblical story of creation.

The Neptunism has roots that go back to Thales of Miletus. Accordingly, the rocks form exclusively by sedimentation from aqueous solutions. Its main representative was the Head of the newly established Mining Academy in Freiberg, Abraham Gottlob Werner ( 1749-1817 ). Volcanic phenomena he explained as insignificant, local Erdbrände, and the resulting rocks were merely melted sediments.

One of the counterparty Werner was the Scottish " gentleman farmer " James Hutton ( 1726-1797 ). The plutonism of the view that the origin of all rocks is to be found in igneous and volcanic processes. All of these ideas are based ultimately on the "dry" and " moist exhalations " of Aristotle. Molten masses from the Earth's interior are making, therefore, from time to time, make their way to the top and can even break through to the surface. Due to the erosion, these rocks are uncovered and re removed to be deposited on the mainlands as soils and oceans as sediments. Due to the weight of ever new sediment layers, the older layers are becoming more entrenched and finally, again heated under enormous pressure and converts until they finally remelted. This idea of ​​the cycle of rocks is now generally accepted.

Various exaggerated views of Neptunists could be refuted in the sequence, such as the origin of granites and basalts as chemical precipitation from the waters of a hot primeval ocean. Therefore, it is often claimed, particularly in the Anglo-Saxon literature that Plutonists would have won the controversy. One must not forget, however, that various assumptions Hutton could not be held, as the total denial of the existence of chemically precipitated sediments, the explanation of the salt domes as magmatic intrusions, and especially the adoption of the water insolubility of the silicates. On the contrary, water plays in all igneous and metamorphic processes an indispensable role. At this point Werners are superheated, mineral- saturated solutions ( brines ), under the name of fluids returned to the theory.

Werner's merit was also that not only researched the mining academies, but was also taught systematically. Many eminent contemporaries, such as Alexander von Humboldt, Novalis and Goethe ( the important experiments on the solubility and precipitation of silica gel undertook ) attended the lectures and spread the interest in geological problems in the world.

Beginning of the 19th century, the various loose ends began to coalesce. Students Werner made ​​on their extensive travels acquaintance with undoubtedly volcanic formations, such as the Auvergne in France, or the Eifel, and modified their views accordingly. On the other hand, they tried the various " rock formations " with the adjacent stratigraphic sequences, as they were observed in Thuringia, in the Paris basin, or in England, to correlate to the type Werners. With the methods of William Smith these could concretely shown in geological maps and profiles. It was made increasing use of Leitfossilen.

An eternally current world, or a universe of disasters?

Especially the study of index fossils led to another, long-lasting controversy about the role that we must ascribe the catastrophic events in Earth's history. As the main representative of the Kataklysmentheorie applies Georges de Cuvier ( 1769-1832 ). From the often dramatic differences in the fossil record of the individual formations, he concluded that in the course of the earth huge upheaval must have taken place, which would have wiped out all living things in certain areas. After this had been replaced by new ones, either immigrated from outside, or completely newly created organisms. The Biblical Flood had been present only the very last of these disasters.

The concept of uniformity was developed by Sir Charles Lyell ( 1797-1875 ). His major work, Principles of Geology, first published 1830. Based on the idea of ​​James Hutton, Lyell came to the conclusion that the geological time scale, compared to human history is very long. He also assumed that the processes that led to the formation of certain rocks, are essentially identical to the operations that can be observed today. ( " The present is the key to the past " ) The changes in the fossil record Lyell explained by continuous, slow rise and fall of the Earth's crust, as it had already been introduced Aristotle. The layer boundaries at which the creatures apparently abruptly changed, simply correspond to the times in which no sediments were deposited at the senior mainlanders.

It was Charles Darwin (1809-1882) largely helped the actualism breakthrough. In his youth he had received a formal, albeit brief, trained as a geologist, and his explanation of the origin of the atolls is accepted today. His greatest achievement, however, the theory of evolution, largely based on Lyell's aktualistischem principle. Only through the comparative study of living organisms today he put the paleontology on a solid theoretical foundation. Darwin returned with his theory of natural selection, the tool with which one can explain the slow change of the organisms in the course of the earth, without spending completely unknown, arbitrary, if not supernatural, having to postulate forces. One of the last paleontologist who biodiversity on a metaphysical causality as followers of catastrophism - a creative God - attributed, Louis Agassiz was.

Nevertheless, it was premature to announce the final victory of Aktualisten. In fact, it was just Lyell very difficult to accept Darwin's theory of evolution. Lyell's prediction that one would have to look for remains of vertebrates in the oldest layers, however, never fulfilled. Also, the late appearance of man, and at that time growing signs of a global ice age, contradicting his view that the earth would never have changed considerably in its history. In recent times, the already believed dead catastrophism experienced a renaissance. The idea of long, stable geological epochs in which virtually nothing changed, includes the possibility of one-time, sudden, catastrophic upheavals (such as meteorite impacts ) ultimately not enough.

The first global hypotheses on the formation of mountains

During the 19th century, more and more individual data were mainly collected worldwide. Gradually formed a generally accepted, relative geological time scale out. The different states based their respective geological institutes devoted particularly to the production of national cartography and exploration of deposits.

The Katastrophist Léonce Élie de Beaumont (1798-1874) developed the first comprehensive theory of mountain building ( orogeny ). Accordingly, the global mountain belt would arise through the cataclysmic volcanic eruptions accompanied by cooling of the Earth, similar to the shrinking of skin growing cold Bratapfels.

In the Swiss Jura, and especially in the coal fields of the Appalachian Mountains in North America, more and more evidence were discovered actually that pointed to significant lateral narrowing of rock strata. These movements were guided there seems to extensive formation of wrinkles and tectonic thrusts. In 1873, the American James Dwight Dana Aktualist ( 1813-1895 ) summarized these observations to his Geosynklinal theory together. This remained until well into the 20th century, the relevant tectonic model of explanation. In Europe helped Eduard Suess (1831-1914), with his work on the Alps, such ideas to break through. In Suess also has the distinction of global mountain building phases decreases. Best known are the Caledonian, Variscan and Alpidic Gebirgsbildungsära. Hans Stille (1876-1966) took until the twenties of the 20th century with great success the contraction hypothesis, according to which the orogeny esp. by the shrinkage of the earth is called out ( silence ) cycle.

The problem with this hypothesis is that it is not able satisfactorily to explain certain expansive phenomena, such as the depression of grave fractures or Spaltenvulkanismus. Moreover, it remains unclear how a continuous cooling process should lead to cyclically recurring phases of the orogeny, which are separated by long periods of tectonic calm. Only the discovery of natural radioactivity provided a plausible source of energy that could counteract the previously assumed, unstoppable cooling and shrinking process of the earth. But even then, the phenomenon of mountain formation cycles remained enigmatic.

The search for the entrenched supercontinent

In the second half of the 19th century, more and more similarities between the deposits and fossils have been discovered on different continents, particularly in South America, Africa and India. We therefore postulated the existence of land bridges that would have the continents joined together earlier, as now, the Isthmus of Panama connects North and South America. Suess, however, assumed that large parts of the country were originally contiguous Gondwana fallen and had been transformed into ocean floor. It is precisely this idea was well received by the way in occult and esoteric circles to Madame Helena Blavatsky. Not only the demise of Atlantis, but also of Lemuria ' ( the supposed original homeland of the lemurs ) in the Indian Ocean, and from Mu in the Pacific, was the result of ' media ' painted imaginative, and with the theory of the Ozeanisierung of continental crust explains.

Until the mid-20th century into the most diverse geotectonic hypotheses have been proposed, such as the Pulsationshypothese posed by alternating periods of contraction and expansion of the earth, or the oscillation hypothesis, which relies increasingly on vertical isostatic movements in the earth's crust. Like their predecessors, so all these hypotheses have in common that they start from a solid fixation of the earth's crust on its basis.

Especially Italian, German geophysicist and later began the construction of seismographs with which the propagation waves could be recorded earthquakes in the Earth's body. Around 1900 Emil Wiechert closed ( 1861-1928 ) from seismic data to the shell structure of the Earth, with the Earth's core, mantle and crust.

The discovery of the drifting continents

From about 1930 such of Mobilism and a moving Earth's crust sat down instead of models of Fixismus increasingly. It emerged the contraction theory and its opposite, the expansion theory of the earth. Both had a lot going for it, but could not explain all phenomena. The final paradigm shift came with results of deep drilling and by research vessels of Oceanography.

When laying the first submarine telephone cable from the British Isles to North America at the end of the 19th century, discovered the Mid-Atlantic Ridge. However, it took a long time no conclusions from the fact that he was parallel to the coast stretching from north to south through the whole ocean, rather than, as would have expected to connect the continents on both sides of the Atlantic in the east-west direction.

The first mobilistic ideas about the possibility of significant lateral movements of land masses are found in the continental drift hypothesis, Alfred Wegener (1880-1930) from the year 1915. Wegener assumed that the relatively light granitic rocks of the continental crust ( sial ) on the denser, but viscous ground of basaltic material ( Sima ) swim, like icebergs floating on the water. An original supercontinent ( Pangaea ) could break into pieces, and disperse them so by relatively weak forces. This would not only the parallel course of the eastern and western shores of the Atlantic to explain, but also the similarities of fossils and climate witnesses, as well as certain old mountain ranges in Gondwana. Wegener's theory came during his lifetime but widely rejected because he could not plausibly explain the forces at work. Only Arthur Holmes (1890-1965) proposed in 1930 a mechanism that could explain the movement of tectonic plates: convection currents of hot magma in the mantle.

The breakthrough mobilistischer theories it was carried out three decades later. It was recognized that the global system of mid-ocean ridge is seismically active, and that there, continuously new material from the mantle rises to the surface along volcanic columns. In Iceland, situated exactly on the Mid-Atlantic Ridge, paleomagnetic measurements of rocks on the ocean floor has been proven that move the two symmetrical sides of the ocean floor every year a few inches apart with help. This phenomenon is today, with a not entirely happy translation from English, as seafloor spreading referred to (see: Sea -Floor Spreading ), ocean floor spreading would be more appropriate. From a wealth of geophysical, oceanographic, paleontological and petrographic observations suggest the now generally accepted theory of plate tectonics developed. The cyclic alternation of phases of the breakup of continents, and the next collision of these plates provides a plausible explanation for the recurring, global mountain building phases ( Wilson cycle) as well as a number of other geological phenomena.

The change in working methods in the 20th century

Already in the 18th and 19th centuries, geologists began to refer to chemical and physical methods for the study of rocks and minerals. Here are primarily going back to Axel Frederic CRONSTEDT Lötrohrprobierkunde and the increasingly important in the 19th century wet chemical analysis mentioned. However, by the beginning of the 20th century was dominated in geology descriptive research methods. In the 20th century, the geology changed to an analytical science: With the discovery of X-ray diffraction could be the mineralogical composition of finely crystalline rocks also determine the development of geophysics you won the first time insights into the bowels of the earth. With the help of computer modeling geological processes can be better understood. An increasing proportion of geological research wandered from the site to the desk and into the lab. This change in methods made ​​from the previously purely qualitative geology a quantitative science, and thus provides after departure from metaphysical ideas in the early modern period represents the second quantum leap in the history of science of geology

Outlook and open questions

The Fixismus is now considered largely obsolete, although he had developed consistently from the once " victorious " actualism, and also from the " victorious " plutonism, with his contempt of the water and the oceans. But if you look at the history of geology, it would not be surprising if certain aspects of the Fixismus would eventually penetrate through the back door into the theory. In fact, also arise in the context of plate tectonics still several unresolved issues:

• Why was the supercontinent Pangaea stable so long? Have the convection stood just be quiet at this time? In general, the exact distribution, number and shape of these convection cells is far from clear.
• But why not find yourself between Africa, India and Antarctica, as well as well-developed between Antarctica and Australia mid-ocean ridge, between Australia and India?
• Why belong, according to radiometric measurements, of all the rocks of the St. Paul's Rocks, right on the Mid-Atlantic Ridge, with the oldest in the world?

Therefore, the conclusion of a little joke, which already by the Bishop of Durham, Richard de Bury (1287-1345), could have come to use the term " Geologia " first introduced to distinguish the doctrine of the earthly things of theology " What is the difference between a theologian and a geologist? Theologians have never been up there. ' Geologists have never been down there. '"