geology

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The Geology ( ancient Greek γῆ gē "earth" and -logie is) the science of the structure, composition and structure of the earth's crust , the properties of its rocks and its development history and the processes that shaped the Earth's crust and, to date form. The term is also used for geological structure , such as The Geology of the Alps .

The term geology in today's sense is first used in 1778 by Jean-André Deluc (1727-1817). In 1779, Horace-Bénédict de Saussure (1740–1799) introduced it as a fixed term . Before that, the term geognosy was used .

Main features

A geologist takes the first look at the rock samples in a fresh drill core.

Geologists deal with the earth's crust, rocks, and oil and gas . Both the spatial relationships between different rock bodies and the composition and internal structure of the individual rocks provide information for deciphering the conditions under which they were formed. The geologist is responsible for the detection and development of raw materials such as metal ores, industrially used minerals as well as building materials such as sand, gravel and clays and, more recently, silicon for the solar industry, without which further economic development would not be possible. In addition, he is also active in securing drinking water as well as energy resources such as oil, gas and coal. Ultimately, the geologists are responsible for exploring the subsoil, especially in the case of larger construction projects, in order to avoid subsidence, landslides and ground fractures in the long term.

Off-road or underground geologist divides the open-minded (open-access) rocks on the basis of external features into defined units. It must be possible to represent these mapping units at the selected scale on a geological map or in a geological profile . By extrapolation , he can predict how the rocks are stored underground with a high degree of probability.

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

Such detailed, small-scale investigations provide the data and facts for large-scale investigations in general geology.

Geology has many points of contact with other natural sciences , which are summarized as geosciences . Geochemistry looks at chemical processes in the earth system - and uses methods from chemistry to obtain additional information on geoscientific issues. The same applies to geophysics and geodesy . Even mathematics has produced a special branch, geostatistics , which is particularly used in mining . Since the 1970s there has been a certain trend in the geosciences in general from qualitatively descriptive investigations towards more quantitative measuring methods. Despite the increased computing power of modern computers, such numerical methods still reach their limits due to the enormous variability and complexity of geoscientific parameters.

In the border area to astronomy , the planetary geology or astrogeology moves as a branch of planetology , which 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 have gained in importance, especially since the beginning of space travel and the exploration of our solar system with probes and satellites .

History of geology

Even in antiquity , people had long had practical knowledge of how to search for mineral raw materials , how to mine and use them. The first attempts at a theoretical treatment of geological questions, such as the cause of earthquakes or the origin of fossils , can only be found in the Ionic natural philosophy in the 5th century BC. Until the early modern times, the teaching of Empedocles about the four elements and the teaching of Aristotle about the transmutation of the elements also pointed the way for ideas about the nature of metals , minerals and rocks .

During the decline of the Roman Empire in late antiquity, these views were only passed down in the eastern, Greek-influenced part, where they were taken up again in the early Middle Ages by Arab scholars such as Ibn Sina . In Western Europe, on the other hand, much practical knowledge of mining was lost again. It was not until the 12th and 13th centuries that occidental alchemists began to deal again with the formation of metals and rocks inside the earth. In the course of the Renaissance , such speculations were not only expanded by humanistic scholars such as Paracelsus , but also supplemented by extensive empirical data and practical methods, especially by Georgius Agricola . From such approaches a kind of “proto-geology” developed up to the 17th century, which had many similarities with the “proto-chemistry” of the economist, alchemist and mining engineer Johann Joachim Becher .

The Danish natural scientist Nicolaus Steno took an important step towards establishing geology as an independent science by introducing the stratigraphic principle in 1669 . With this he established the principle that the spatial storage of sediment layers on top of each other actually corresponds to a chronological sequence of rock deposits one after the other . Even Robert Hooke speculated about the same time, if one can not reconstruct the historical course of rock formation from the fossil content of the rock.

In the course of the 18th century, mine managers and engineers increasingly tried to gain a theoretical understanding of geological relationships. In the middle of the century they developed 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 . James Hutton (1726–97) is considered to be the founder of Plutonism with his postulate that all rocks are of volcanic origin. Hutton also popularized the idea that earth's history is many orders of magnitude longer than human history. The Neptunists were led by Abraham Gottlob Werner (1749–1817), with the now-rejected basic assumption that all rocks are deposits of a primordial primordial ocean. From the combination of magmatism , sedimentation and rock transformation , the idea of the rock cycle developed .

Around 1817, William Smith established the use of index fossils for the relative dating of the layers of a sedimentary sequence.

Around the period from 1830 to 1850, the dispute between catastrophism in the footsteps of Georges de Cuvier (1769–1832) and actualism around Sir Charles Lyell (1797–1875) formed the second great controversy in the history of geology. While the catastrophists assumed sudden and global upheavals in the history of the earth, with subsequent re-creation of the exterminated living beings, the actualists emphasized the steady and steady development of the earth in countless small steps that gradually accumulate over long periods of time ( 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 dealt increasingly with the problems of mountain formation and the global movements of the earth's crust. Until well into the 20th century, the idea, which goes back to Léonce Élie de Beaumont (1798–1874), dominated that the global mountain belts were the result of the cooling and shrinking of the earth's body. James Dwight Dana (1813–1895) developed the geosyncline theory around 1875 from the observation of folded and tectonically disturbed rocks . This tectonic explanatory model was significantly further developed by Eduard Suess (1831–1914) and Hans Stille (1876–1966).

The geotectonic hypotheses were dominated by the principle of fixism . The position of the continents and oceans to one another was largely unchangeable. Lateral movements of the earth's crust, the traces of which could be observed in fold mountains or on regional crevice systems, were viewed as largely local phenomena. In contrast, vertical movements of the earth's crust were considered to be decisive for the lowering of ocean basins or the rise of land bridges between the continents.

The first important ideas about the possibility of significant horizontal movements of mainland masses can be found in Alfred Wegener's (1880–1930) continental drift hypothesis from 1915. However, the breakthrough of mobilism did not come until three decades later, as fundamentally new observations in geophysics and oceanography led to the development of the now generally accepted theory of plate tectonics .

General geology

Geologist's tools: pick hammer and magnifying glass .

General geology deals with the forces that act on the earth's body and with the processes that contribute to rock formation on a large scale .

Every rock can be assigned to one of the three major rock classes based on its specific formation ( structure , structure ): sedimentary rocks , magmatites and metamorphic rocks . Each rock can be transformed into a rock of the other two families by geological processes (see: cycle of rocks ). The processes that work on the earth's surface are called exogenous, those in the earth's interior are called endogenous.

Exogenous dynamics

The exogenous dynamics (also exogenous processes ) are generated by forces acting on the earth's surface such as gravity, solar radiation and rotation of the earth and lead to the formation of sedimentary rocks . This is done through

Soil science deals with a separate, complex area of ​​exogenous processes . The Quaternary is concerned with the operations and deposits of the last ice age in the Quaternary that characterize a large part of today's landscapes in the northern hemisphere.

Endogenous dynamics

The endogenous dynamics (also endogenous processes ) are based on forces within the earth's crust, such as tensions, heat development through radioactive decay processes or the earth's magma core and lead to the formation of metamorphites and magmatites . It starts with the

  • Increase in pressure , with the continued deposition of further sediments on the underlying layers. Through drainage, compaction and solidification ( diagenesis ), the loose sediments become solid rock, such as sandstone .
  • The deformation of rocks and the recrystallization of minerals, under increasingly higher temperatures and increasing pressure, is called metamorphosis . The rock initially remains in a solid state. Ortho and para gneisses are often formed from igneous rocks and coarse-grained sediments, and slate from fine sediments .

The movements that move, deform and fold the surface rocks into the depths, but at the same time bring the deep rocks back to the surface, as well as the traces that these forces leave in the rocks, such as folding , shear and foliation , are determined by tectonics and the Structural geology investigated.

Historical geology

The historical geology explores the history of the Earth from its formation to the present day, in general, and the evolution ( evolution ) of living organisms in particular. With this historical approach, geology (together with physical-astronomical cosmology ) represents an exception within the natural sciences. The latter deal primarily with the actual state of their study object and less with its becoming . The formation of rocks (lithofacies) and the fossils enclosed in them (biofacies) serve as sources of information in geology . The structure of the earth's history in a geological time scale is done by stratigraphic and geochronological methods.

stratigraphy

The basis of the stratigraphy provides a simple principle: the storage rule . A layer in the hanging wall ('above') was deposited later than the layer in the horizontal ('below'). However, it should be noted that layers originally deposited horizontally may be dislocated or even overturned by later tectonic movements. In this case, one has to rely on the existence of clear top-bottom criteria to determine the original position. Furthermore, layers that overlay such dislocated rocks with a discordance , i.e. at an oblique angle to the stratification, are also younger than the latter. The same also applies to igneous channels and intrusions from the depths that penetrate the layers from below.

Geological profile through northwest Germany

When creating a stratigraphic profile , particular knowledge of paleontology is used. If the remains of a certain living being occur only in very specific layers, but at the same time have a wide, supra-regional distribution and are as independent as possible of local variations in the deposition conditions, then one speaks of a guide fossil . All layers in which these key fossils are found are therefore of the same age. Only when there are no fossils is it necessary to resort to lithostratigraphy . Then the simultaneity of certain layers can only be demonstrated with lateral interlocking.

In order to reconstruct tectonic processes, the geologist examines the displacement and deformation of the rocks due to fissures , foliation , faults and folding . Here, too, the most recent structures are those that penetrate the others but are not themselves offset. The art here is "to see the intricate simple, the dormant in motion." ( Hans Cloos )

geochronology

Aeonothem Arathem system Age
( mya )
Phanerozoic
Duration: 541 Ma 		Cenozoic
Modern Earth
Duration: 66 Ma 		quaternary 0
⬍
2.588
Neogene 2,588
⬍
23.03
Paleogene 23.03
⬍
66
Mesozoic
Middle Ages
Duration: 186.2 Ma 		chalk 66
⬍
145
law 145
⬍
201.3
Triad 201.3
⬍
251.9
Paleozoic
Paleozoic
period: 288.8 Ma 		Perm 251.9
⬍
298.9
Carbon 298.9
⬍
358.9
Devon 358.9
⬍
419.2
Silurian 419.2
⬍
443.4
Ordovician 443.4
⬍
485.4
Cambrian 485.4
⬍
541
P
r
ä
k
a
m
b
r
i
u
m
Length: 4,059 Ma 		Proterozoic
Duration: 1,959 Ma 		Neoproterozoic
Young Proterozoic
Duration: 459 Ma 		Ediacarium 541
⬍
635
Cryogenium 635
⬍
720
Tonium 720
⬍
1000
Mesoproterozoic
Middle Proterozoic
Duration: 600 Ma 		Stenium 1000
⬍
1200
Ectasium 1200
⬍
1400
Calymmium 1400
⬍
1600
Paleoproterozoic
Ancient Proterozoic
Duration: 900 Ma 		Statherium 1600
⬍
1800
Orosirium 1800
⬍
2050
Rhyacium 2050
⬍
2300
Siderium 2300
⬍
2500
Archean
Period: 1,500 Ma 		Neo-Archaic
Duration: 300 Ma 		2500
⬍
2800
Mesoarchean
Duration: 400 Ma 		2800
⬍
3200
Paleoarchean
Duration: 400 Ma 		3200
⬍
3600
Eoarchic
Duration: 400 Ma 		3600
⬍
4000
Hadaikum
Duration: 600 Ma 		4000
⬍
4600

A fundamental problem here is the fact that with the above methods only a relative time scale , a before-and-after of the various rock formations, is obtained, but no absolute dates. Attempts were made early on to estimate the sedimentation rates of certain rocks, but most of the time is not in the layers themselves, which can have formed in a relatively short time, but mainly in the gaps between the layers and in the Discordances between different shift packages. That is why the absolute time scale , which was obtained with the help of annual rings in trees ( dendrochronology ) or by counting the varveal layers in deposits from the last Ice Age, only reached a few thousand years ago.

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

See also: dating , cosmology , formation of the earth , rubidium-strontium method , potassium-argon method , radiocarbon method , as well as the more detailed paleo / geological time scale

Actualism

In order to be able to draw conclusions about the past from the current situation, the geologists use the principle of actualism . This can be summarized in one sentence: The key to the past is the present. If a geologist finds z. If, for example, old rocks are almost identical to the lavas that have flowed out of a volcano that is active today, then he can assume that the rock found is also volcanic material. However, the actualism cannot be applied to all rocks. The formation of iron ore deposits (BIF - "Banded Iron Formations") can no longer be observed today, for example, because the chemical conditions on earth have changed to such an extent that the formation of such rocks no longer takes place. Other rocks may form at such depths that their formation is beyond human reach. In order to understand the formation of such rocks, the geoscientists resort to laboratory experiments.

Applied geology

Applied geology deals with the practical utilization of geological research in the present. The benefit consists not only in the efficient exploitation of the earth's natural resources, but also in the avoidance of environmental damage and the early warning of natural disasters such as earthquakes , volcanic eruptions and tsunamis . It is divided into a large number of different fields that interlock with each other and with other sciences. See: Geosciences

Some important areas of applied geology are, for example:

  • the hydrogeology , which deals with the flow behavior and the quality of the (ground) water and is important for the production of drinking water and flood protection;
  • the Engineering Geology , for example, is dedicated to the statics of the floor in the construction of buildings;
  • the economic geology or mining geology , which is the oldest area of research in geology with the study of natural mineral resources is concerned (coal, oil, gas, ores, etc.);
  • the soil science that deals with the quality, composition and horizontal sequence of soils;
  • the environmental geology .

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

See also

Portal: Geosciences  - Overview of Wikipedia content on geosciences

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