Geology

The geology (Greek γῆ [ ɡɛ ː ] 'earth', and λόγος [ lɔɡɔs ] 'doctrine' ) is the science of the structure, the composition and structure of the earth, their physical characteristics and their development history, and the processes that they formed and also still form. Notwithstanding the actual significance used the word for geological structure, such as the geology of the Alps.

The term geology in the modern sense is first found in 1778 by Jean- André Deluc ( 1727-1817 ). Horace - Bénédict de Saussure (1740-1799) resulted in geology in 1779 as a fixed term. Previously the term was in use geognosy.

• 4.1 stratigraphy
• 4.2 geochronology
• 4.3 actualism

• 8.1 Professional associations
• 8.2 Universities (incl. Free course material )

Broad

The material with which geologists mainly deal with the building blocks of the earth's crust, such as rocks or the water stored in them ( Hydrogeology ) or oil and gas are ( Petro geology). Both the spatial relationships between different rock bodies, as well as the composition and internal structure of the individual rocks, provide information to decipher the conditions under which they are incurred. The geologist is responsible for the detection and the development of a variety of raw materials such as metal ores, industrial minerals and construction materials such as sands, gravels and clays, would not be without the further economic development possible. In addition, he is also responsible for the security of drinking water and energy resources such as oil and gas and coal and recently silicon for the solar industry. Finally, the geology is responsible for the exploration of the subsoil, especially on larger construction sites to prevent subsidence, landslides, and ground ruptures in the long term.

In terrain or underground geologist divides the open-minded ( open-access ) rocks on the basis of external characteristics into defined units. These mapping units must be at the scale selected on a geological map or a geological profile, represent. So he can predict how the rocks are stored in the subsoil most likely through extrapolation.

The detailed analysis of the rocks ( petrography, petrology ) but usually takes place in the laboratory.

• With the individual, sometimes microscopic, constituents of the rocks, the minerals, the mineralogy is concerned.
• The fossil content of sedimentary rocks dealt paleontology.

Such detailed studies on a small scale provide the facts and figures for the large-scale studies of the general geology.

The geology has many points of contact with other natural sciences, which are summarized as geosciences. Thus, the geochemistry considered chemical processes in the Earth system - and uses methods from chemistry to obtain additional information on geoscience issues. The same applies to the geophysics and geodesy. Even mathematics has a special branch, geostatistics, produced, which finds particular use in the mining industry. Since the 1970s, consists in the geosciences in general a certain trend of more qualitative, descriptive studies to more quantitatively measuring methods. Despite the increased processing power of modern computers encounter such numerical methods, because of the enormous variability and complexity of geoscientific parameters still to their limits.

In the border area to astronomy, the Planetary Geology and Planetary Geology moves as a branch of planetary science that deals with the composition, the internal structure and the forming processes on foreign celestial bodies. Geological issues and the application of geological methods outside the Earth won especially since the beginning of space travel and the exploration of our solar system with probes and satellites in importance.

History of Geology

Even in ancient times, people have long possessed a working knowledge in the search for mineral resources, their degradation and recovery. The first attempts of a theoretical treatment of geological issues, such as the cause of earthquakes, or the origin of fossils can be found, however, only in the Ionian natural philosophy in the 5th century BC until the early modern era, the doctrine of Empedocles was of the four elements and Aristotle's doctrine of the transmutation of the elements provide direction for the ideas about the nature of metals, minerals and rocks.

During the decline of the Roman Empire in Late Antiquity, these views have been handed down only in the eastern, Greek -embossed section, where they were resumed in the early Middle Ages by Arab scholars, such as Ibn Sina. In Western Europe, however, even a lot of practical knowledge in the mining industry were lost again. Only in the 12th and 13th century Western alchemists began again to deal with the formation of metals and rocks inside the earth. During the Renaissance such speculations were not only expanded by humanist scholars, such as Paracelsus, but also supplemented by extensive empirical data and practical methods, especially Georgius Agricola. From these beginnings, a kind of " proto- geology ", which had many similarities with the "Proto - chemistry" of economists, alchemists and mining engineer Johann Joachim cup developed until the 17th century.

An important step in establishing of geology as an independent science was the Danish naturalist Nicolaus Steno, by 1669 the stratigraphic principle introduced. By this he established the principle that the spatial storage of sediment layers in reality, a temporal sequence of sediments that corresponds to one over the other in sequence. Robert Hooke also speculated about the same time, if one could not reconstruct the historical sequence of rock formation from the fossil contents of the rocks.

In the course of the 18th century, mine managers and engineers sought increasingly to a theoretical understanding of geological contexts. Here they developed mid-century the basic methods of geological mapping and the creation of stratigraphic profiles.

The beginning of geology as a modern science is usually set with the controversy between the schools of thought of plutonism and Neptunism. As the founder of plutonism applies James Hutton ( 1726-97 ) with his postulate, all rocks are of volcanic origin. Hutton also popularized the idea that the earth's many orders of magnitude is longer than human history. The Neptunists were led by Abraham Gottlob Werner (1749-1817), with the now discarded basic assumption that all rocks are deposits of a primordial primeval ocean. The combination of magmatism, sedimentation and rock alteration the idea of ​​the cycle of rocks developed in the following.

1817 established William Smith the use of Leitfossilen for relative dating of rock layers within a stratigraphic sequence.

At about the time from 1830 to 1850 made ​​the argument between catastrophism in the footsteps of Georges de Cuvier ( 1769-1832 ), and to Sir Charles Lyell 's actualism ( 1797-1875 ), the second major controversy in the history of geology. While the Katastrophisten of sudden and global upheavals emanating in Earth, with subsequent re-creation of the extinct creatures that Aktualisten stressed the uniform and steady development of the Earth in many small steps that in the course of long periods gradually accumulate ( gradualism ). Even Charles Darwin (1809-1882) followed in his theory of evolution, with their slow development of new biological species, largely the actualistic principle.

As a result, the geologists involved more with the problems of orogeny and the global movements of the earth's crust. Until well into the 20th century which, on Léonce Élie de Beaumont ( 1798-1874 ) dominated declining notion that the global mountain belt the result of the cooling and contraction of the earth are. From the observation of folded and tectonically disturbed rocks developed James Dwight Dana (1813-1895) around 1875 the Geosynklinal theory. This tectonic model of explanation was by Eduard Suess (1831-1914) and Hans Stille (1876-1966) significantly enhanced.

Here, the geotectonic hypotheses were dominated by the principle of Fixismus. The position of the continents and oceans each other was seen as largely immutable. Lateral movements of the earth, whose traces could be observed in fold mountains or in regional columns systems were considered to be largely local phenomena. On the other hand were vertical crustal movements as crucial for the reduction of ocean basins, or the rise of land bridges between the continents.

The first important ideas about the possibility of significant horizontal movements of land masses, can be found in the continental drift hypothesis, Alfred Wegener (1880-1930) from the year 1915. Breakthrough of Mobilism it was carried out three decades later, as a fundamentally new observations of Geophysics and oceanography for the development of the now generally accepted theory of plate tectonics led.

General Geology

The general geology is concerned with the forces that act on the Earth's body and contribute to the processes on a large scale for rock formation.

Each rock can be assigned according to its specific education ( fabric, structure), one of three major classes of rock: sedimentary, igneous and metamorphic rocks. Each rock can be transformed by geological processes into a rock in the other two families (see: cycle of rocks ). The processes that act on the surface, are used as exogenous, indicating in the earth as endogenous.

Exogenous dynamics

The exogenous dynamics ( exogenous processes) is generated by acting on the surface forces such as gravity, sun exposure, and rotation of the Earth and leads to the formation of sedimentary rocks. This is done by

• Physical erosion of other rocks by wind, water or ice, and mass movements of large quantities of rock, such as rock falls,
• Chemical weathering,
• Physical deposition of the crushed material ( detritus ), such as garbage dumps, as gravel, sand, clay, etc. and the subsequent consolidation of the sediments of hard rocks ( diagenesis )
• Chemical precipitation of evaporites ( such as inorganic limestone, gypsum, salt) and
• Biogenic formation of sediments (as most limestones or diatomite).

A private, complex area of exogenous processes treated soil science. The Quaternary geology deals with the deposits of the last glacial periods of the Quaternary, which characterize a large part of today's landforms on the northern hemisphere.

Endogenous dynamics

The endogenous dynamics ( endogenous processes) based on forces within the earth's crust, such as voltages, heat generation by radioactive decay processes or the magma core of the earth and leads to the formation of metamorphic and igneous rocks. It begins with the

• Increasing the pressure of the continuous deposition of other sediments on the subjacent layers. By drainage, compaction and consolidation ( diagenesis ) is derived from the unconsolidated sediments solid rock, such as sandstone.
• The deformation of rocks and the recrystallization of mineral, under increasingly higher temperature and increasing pressure is referred to as metamorphosis. Here, the rock but initially remains in the solid state. From igneous rocks and coarse-grained sediments often occur ortho-and para - gneisses, fine sediments shale.

• Finally, it may yet come to the melting of the rocks ( anatexis ). Glutflüssige magmas then rise again from the mantle.
• If the magmas stuck in the earth's crust and allow to cool to form plutonic rocks, such as granite, when they reach the Earth's surface, resulting in the formation of igneous rocks such as lava or volcanic ash.

The movements who will ship the surface rocks into the deep, deform and fold, but at the same time bring the plutonic rocks back to the surface, as well as the traces left by these forces in the rocks, such as folding, shearing and foliation are of the tectonics and the structural Geology investigated.

Historical Geology

The historical geology explores the history of the world from creation to the present day in general, and the history of development (evolution) of living beings in particular. With this historical approach, the geology (together with the physico- astronomical cosmology ) an exception within the natural sciences dar. latter deal mainly with the actual state of their object of study and less to do with its becoming. The sources of information used in geology, the formation of the rocks ( lithofacies ) and the included fossils in them ( biofacies ). The structure of the Earth's history in a geological time scale stratigraphic and geochronological methods done by.

Stratigraphy

The basis of the stratigraphy provides a simple principle: the storage rule. A layer in the hanging wall ( 'above' ) was later deposited as a layer in the footwall ( 'down' ). However, it should be noted that originally deposited horizontal layers may even be overturned adjusted by later tectonic movements or. In this case one has to rely on the existence of unique up-down criteria, to determine the original storage. The principle that layers that overlie rocks with such feigned an unconformity that is oblique to the bedding, also younger than the latter. The same is also true for magmatic intrusions and transitions from the deep, penetrate the layers from the bottom.

When creating a stratigraphic profile particularly findings of paleontology are applied. When the remains of a certain organism occur only in certain layers, but at the same time have a broad, cross-regional distribution, and are as independent as possible from local variations in the deposition conditions, then one speaks of an index fossil. All layers in which to find these index fossils, thus have the same age. Only if no fossils are available, one must take refuge in the lithostratigraphy. Then the time equality of certain layers can only be detected in lateral teeth.

In order to reconstruct tectonic processes, the geologist examines the displacement and deformation of rocks by fracturing, foliation, faults and folding. Here are those structures, the most recent, which break through the others, but themselves are not offset. The art here is " Intricate easy moves to see at rest. " (Hans Cloos )

Geochronology

A fundamental problem here is the fact that you only get a relative time scale, a before -and-after of the various rock formations, but no absolute dating with the above methods. Although they had early attempts sedimentation rates of certain rocks to appreciate, but most of the time does not "come " so in the layers themselves, which may have formed in a relatively short time, but especially in the gaps between the layers and the unconformities between different layer packets. Therefore handed the absolute time scale by means of annual rings in trees ( dendrochronology ), or is derived by counting the varves - stratification in deposits of the last glacial period, only a few thousand years back.

Only with the discovery of natural radioactivity were found reliable methods for absolute dating, even of the oldest rocks. These are based on the known decay rates of radioactive isotopes in the minerals and rocks, and sometimes combined with paleomagnetic measurements.

See also: Dating, cosmology, creation of the earth, rubidium - strontium method, potassium - argon method, radiocarbon dating, such as the detailed paleo / Geological Time Scale

Actualism

In order to draw conclusions about the past from the present situation, the geologists of the principle of uniformitarianism use. This can be summarized in one sentence: The key to the past is the present. Find a geologist eg old rocks that are almost identical to lavas flowed out of an active volcano today, then it can assume that it also is volcanic material in the rock found. However, the actualism can not be applied to all rocks. The formation of ore deposits ( BIF "Banded Iron Formations " ) can be about no longer watching because the chemical conditions on Earth have changed such that the generation of such rocks no longer takes place. Other rocks form may be in such depths that their education is beyond the reach of man. To understand the generation of such rocks, grab the geoscientists back on laboratory experiments.

Applied Geology

The Geology Applied deals with the practical utilization of geological research in the present. The benefit is not only in the efficient exploitation of the natural resources of the earth, but also in the prevention of environmental damage and early warning of natural disasters, such as earthquakes, volcanic eruptions and tsunamis. It is divided into a wide variety of fields, which interlock with one another and with other sciences. See: Earth Sciences

Some important branches of applied geology are for example:

• Hydrogeology, which deals with the flow behavior and the quality of the ( ground) water, and is one for potable water supply and flood protection is important;
• The engineering geology, which is dedicated to, for example, the statics of the ground in the construction of buildings;
• The geology or mining geology, which deals as the oldest research field of geology with the exploration of natural mineral resources (coal, oil, gas, ores, etc.);
• Soil science that deals with the quality, composition and horizontal sequence of soils;
• Environmental geology.

There is a close link of applied geological areas with other disciplines, such as civil engineering, mining and metallurgy, material science or environmental protection.