Important milestones

• - 4600 million years: Formation of the solar system.[15]​.

• - 4.54 Ga: Formation of the Earth.

• - c. 4 Ga: End of the late intense Bombardment, first evidence of life.[16]​.

• - c. 3.5 Ga: Beginning of Photosynthesis.

• - c. 2.3 Ga: Oxygenated atmosphere, first global Glaciation[16]​* 730–635 Ma "Ma (unit of time)"): second global Glaciation.[17]​.

• - 542± 0.3 Ma: Cambrian explosion – Great multiplication of living organisms; first fossil record in abundance; beginning of the Paleozoic.[18]​.

• - c. 380 Ma: First terrestrial vertebrates.[19]​.

• - 250 Ma: Permian-Triassic mass extinction[20]​– At least 90% of all animals on land die; end of the Paleozoic and beginning of the Mesozoic.

• - 65 Ma: Cretaceous-Tertiary mass extinction – Dinosaurs disappear; end of the Mesozoic and beginning of the Cenozoic.[21]​.

• - c. 7 Ma: Appearance of hominids.[22]​.

• - 3.9 Ma: Appearance of Australopithecus, direct ancestor of Homo sapiens.[23]​.

• - 200 ka: Appearance of the first modern Homo sapiens in East Africa.[23]​.

Relative dating

Methods for relative dating were developed when geology first emerged as a natural science. The following principles are still used by geologists today as a means of providing information about geological history and the timing of geological events.

• - The principle of uniformitarianism states that the geological processes observed at work that modify the Earth's crust today have functioned in very similar ways throughout geological time.[24]​ A fundamental principle of geology proposed by the 19th-century Scottish physician and geologist James Hutton is that "the present is the key to the past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now."[25]​.

• - The principle of intrusive relationships refers to transversal intrusions. In geology, when an igneous intrusion passes through a sedimentary rock formation, it can be determined that the igneous intrusion is younger than the sedimentary rock. Different types of intrusions include strains, laccoliths, batholiths, sills and dikes.

• - The principle of transversal relationships refers to the formation of faults and the age of the sequences through which they cut. The faults are younger than the rocks they cut; Consequently, if a fault is found that penetrates some formations but not those above it, then the formations that were cut are older than the fault, and those that are not cut must be younger than the fault. Finding the key platform in these situations can help determine whether the fault is a normal fault or a thrust fault.[26]​.

• - The principle of inclusions and components states that, with sedimentary rocks, if inclusions (or clasts) are found in a formation, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for gravel from an older formation to be broken up and included in a newer layer. A similar situation with igneous rocks occurs when xenoliths are found. These foreign bodies are collected as magma or lava flows, and incorporated and then cooled in the matrix. As a result, xenoliths are older than the rock that contains them.

• - The original horizontality principle states that sediment deposition occurs as essentially horizontal beds. Observation of modern marine and non-marine sediments in a wide variety of environments supports this generalization (although cross-strata are inclined, the general orientation of cross-strata units is horizontal).[26]​.

• - The principle of superposition states that a layer of sedimentary rock in a tectonically unaltered sequence is younger than the one below it and older than the one above it. Logically, a younger layer cannot slide beneath a previously deposited layer. This principle allows sedimentary layers to be viewed as a form of vertical timeline, a partial or complete record of the time from the deposition of the lowest layer to the deposition of the highest bed.[26]​.

• - The principle of faunal succession is based on the appearance of fossils in sedimentary rocks. As organisms exist during the same period throughout the world, their presence or (sometimes) absence provides a relative age of the formations where they appear. Based on principles that William Smith established almost one hundred years before the publication of Charles Darwin's theory of evolution, the principles of succession were developed independently of evolutionary thinking. The principle becomes quite complex, however, given the uncertainties of fossilization, the location of fossil types due to lateral changes in habitat (facies change in sedimentary strata) and that not all fossils were formed globally at the same time.[27]​.

absolute dating

Geologists also use methods to determine the absolute age of rock samples and geological events. These dates are useful on their own and can also be used in conjunction with relative dating methods or to calibrate relative methods.[28]​.

At the turn of the century, the advancement of geological science was facilitated by the ability to obtain precise absolute dates of geological events using radioactive isotopes and other methods. This changed the understanding of geological time. Previously, geologists could only use fossils and stratigraphic correlation to date sections of rock to each other. With isotopic dates, it was possible to assign absolute ages to rock units, and these absolute dates could be applied to fossil sequences in which datable material was present, converting old relative ages into new absolute ages.

For many geological applications, isotope ratios of radioactive elements are measured in minerals giving the amount of time that has passed since a rock passed its particular closure temperature, the point at which different radiometric isotopes stop diffusing in and out of the crystal lattice.[29][30]These are used in geochronological and thermochronological studies. Common methods include uranium-lead dating, potassium-argon dating, argon-argon dating, and uranium-thorium dating. These methods are used for a variety of applications. Dating of lava and volcanic ash layers found within a stratigraphic sequence can provide absolute age data for sedimentary rock units that do not contain radioactive isotopes and calibrate relative dating techniques. These methods can also be used to determine the emplacement ages of plutons. Thermochemical techniques can be used to determine temperature profiles within the crust, the elevation of mountain ranges, and paleo-topography.

Fractionation of lanthanide series elements is used to calculate ages since rocks were removed from the mantle.

Other methods are used for more recent events. Optically stimulated luminescence and cosmogenic radionuclide dating are used to date surfaces and/or erosion rates. Dendrochronology can also be used for landscape dating. Radiocarbon dating is used for geologically young materials containing organic carbon.

plate tectonics

In the 1960s it was discovered that the Earth's lithosphere, which includes the crust "Crust (geology)") and the rigid upper part of the upper mantle, is separated into tectonic plates that move through the deformable plastic solid upper mantle "Plasticity (mechanics of solids)"), which is called the asthenosphere. This theory is supported by several types of observations, such as seafloor spreading[31][32]​ and the global distribution of mountainous terrain and seismicity.

There is an intimate coupling between plate motion at the surface and mantle convection (i.e., heat transfer caused by the slow movement of ductile rock in the mantle). Thus, oceanic plates and adjacent mantle convection currents always move in the same direction, because the oceanic lithosphere is actually the rigid upper thermal boundary layer of the convective mantle. This coupling between the rigid plates moving on the Earth's surface and the convective mantle is called plate tectonics.

The development of plate tectonics has provided a physical basis for many observations of the solid Earth. Long linear regions of geological features are explained as plate boundaries.[33]​.

For example:.

• - Mid-ocean ridges, elevated regions on the seafloor where hydrothermal vents and volcanoes exist, are seen as divergent edges, where two plates move apart.

• - Volcanic arcs and earthquakes are considered convergent boundaries, in which one plate subducts, or moves, under another.

Transform edges, such as the San Andreas fault system, gave rise to powerful widespread earthquakes. Plate tectonics has also provided a mechanism for Alfred Wegener's theory of continental drift,[34] in which continents move across the Earth's surface over geological time. They also provided a driving force for crustal deformation, and a new setting for observations of structural geology. The power of the theory of plate tectonics lies in its ability to combine all of these observations into a single theory of how the lithosphere moves over the convective mantle.

Earth Structure

Advances in seismology, numerical modeling and mineralogy and crystallography at high temperatures and pressures allow us to understand the internal composition and structure of the Earth.

Seismologists can use the arrival times of seismic waves to obtain images of the Earth's interior. The first advances in this field showed the existence of a liquid outer core (where shear waves" could not propagate) and a solid, dense inner core. These advances led to the development of a stratified model of the Earth, with a crust "Crust (geology)") and a lithosphere on top, the mantle "Mantle (geology)") below (separated in its interior by seismic discontinuities at 410 and 660 kilometers), and the outer core and the inner core below. More recently, seismologists have been able to create detailed images of wave speeds inside the Earth, in the same way that a doctor images a body in a tomography scan. These images have allowed a much more detailed view of the Earth's interior and have replaced the simplified layer model with a much more dynamic model.

Mineralogists have been able to use pressure and temperature data from seismic and modeling studies along with knowledge of the Earth's elemental composition to reproduce these conditions in experimental settings and measure changes in crystal structure. These studies explain the chemical changes associated with the main seismic discontinuities of the mantle and show the crystalline structures expected in the Earth's inner core.

Regional geology

Regional geology") is the branch of geology that studies the geological configuration of each continent, country, region or specific areas of the Earth.

Geology includes different sciences or disciplines, which make up university or professional educational training plans. Due to the great diversity of disciplines or geological sciences, these are grouped into different independent teaching units, where a better modular organization of the teaching and research of Geology on the different sciences it comprises is carried out. One of the general structures in which these departments are composed is:

• - Department of Crystallography and Mineralogy (includes gem mineralogy).

• - Department of Stratigraphy and Sedimentology.

• - Dept. of Geodynamics. Which is subdivided, in turn, into:

• Internal Geodynamics (structural geology, historical geology, tectonics; geophysics and seismology)

• External Geodynamics (geomorphology, hydrogeology and geotechnics; economic and petroleum geology).

• - Department of Paleontology.

• - Dept. of Petrology and Geochemistry (includes volcanology and planetary geology).

A geologist is a specialist and professional in the study, observation or experimentation related to the Earth, its composition, structure, dynamics, origin and evolution. In your professional work you must apply the principles of geoethics.

A geologist stands out for having the following skills:

• - Carry out petrographic studies and chemical analyzes to determine the origin, composition and evolution of rocks.

• - Establishes the stratigraphy of a region and performs structural analysis to establish the genetic order of the geological units in a region and to define both macro-structures and microstructures, in order to describe the tectonic evolution of said region.

• - Prepares geomorphology, morphometry and morphotectonics to establish the relief forms of a region, and the factors that formed them that allow them to identify the areas of greatest energy, basin limits, erodibility and develop their professional activity with a sense of service to society and with attachment to their quality and professional attachment.

• - Carry out geochemical and geophysical studies to determine both the content of ionic species in surface, underground and hydrothermal waters, as well as the chemical composition of rocks, and their applications in the geochemical evolution of natural waters and in mineral prospecting. Determines the physical properties of the Earth's crust, the professional remains critical of scientific progress and the development of its environment.

• - Designs mineral prospecting and exploration studies, performs analysis to determine areas with potential mineral deposits, and quantification. The techniques and parameter determinations are: samples taken, km² explored, meters drilled, drilling efficiency, grade of the samples tested and unit costs.

• - Prepares studies of groundwater and water quality, defines the economic process or processes necessary to define the deposits, extract and manage subsoil water resources with respect for oneself, others and the environment.

• - Designs geotechnical studies to know the physical properties of soils and rocks to determine risk areas or problems of subsidence and active faulting.

• - Carry out the planning, design and development of geological projects to plan, design and develop general and applied geology studies, which will solve specific problems or perform specific tasks within a unitary process or operation.[69]​.

• - Earth Sciences.

• - Geological time scale.

• - Plate tectonics.

• - Annex: Common definitions in geology.

• - Compton, Robert R. (1985). Geology in the field. New York: Wiley. ISBN 978-0-471-82902-7.

• - F. Lutgens, E. Tarbuck, D. Tasa. Essentials of Geology 13th Edition. (2017) 608 pages. ISBN 0134446623, ISBN 978-0134446622.

• - Stephen Marshak. Essentials of Geology Sixth Edition. 720 pages (2019) ISBN 0393667529, ISBN 9780393667523.

• - Wikimedia Commons hosts a multimedia category on Geology.

• - Wikiquote hosts famous quotes from or about Geology.

• - Wikinews has news related to Geology.

• - International Union of Geological Sciences - International Union of Geological Sciences (IUGS).

• - Geological and Mining Institute of Spain (IGME).

• - Geological Studies, Magazine of the National Museum of Natural Sciences (Spain) "National Museum of Natural Sciences (Spain)"), CSIC.

• - Geology Dictionary (Spanish/English) - Mineriaenlinea.com.

• - Colombian Institute of Geology and Mining (INGEOMINAS).

• - EARTH Earth Sciences Thematic Network.

• - Magazine of the Argentine Geological Association.

• - Geology, Mining and Petroleum of Peru.

• - Geology Portal in Spanish.

• - National University of Colombia. Geology Manual for Engineers (2003) Archived August 21, 2016 at the Wayback Machine.

Important milestones

• - 4600 million years: Formation of the solar system.[15]​.

• - 4.54 Ga: Formation of the Earth.

• - c. 4 Ga: End of the late intense Bombardment, first evidence of life.[16]​.

• - c. 3.5 Ga: Beginning of Photosynthesis.

• - c. 2.3 Ga: Oxygenated atmosphere, first global Glaciation[16]​* 730–635 Ma "Ma (unit of time)"): second global Glaciation.[17]​.

• - 542± 0.3 Ma: Cambrian explosion – Great multiplication of living organisms; first fossil record in abundance; beginning of the Paleozoic.[18]​.

• - c. 380 Ma: First terrestrial vertebrates.[19]​.

• - 250 Ma: Permian-Triassic mass extinction[20]​– At least 90% of all animals on land die; end of the Paleozoic and beginning of the Mesozoic.

• - 65 Ma: Cretaceous-Tertiary mass extinction – Dinosaurs disappear; end of the Mesozoic and beginning of the Cenozoic.[21]​.

• - c. 7 Ma: Appearance of hominids.[22]​.

• - 3.9 Ma: Appearance of Australopithecus, direct ancestor of Homo sapiens.[23]​.

• - 200 ka: Appearance of the first modern Homo sapiens in East Africa.[23]​.

Relative dating

Methods for relative dating were developed when geology first emerged as a natural science. The following principles are still used by geologists today as a means of providing information about geological history and the timing of geological events.

• - The principle of uniformitarianism states that the geological processes observed at work that modify the Earth's crust today have functioned in very similar ways throughout geological time.[24]​ A fundamental principle of geology proposed by the 19th-century Scottish physician and geologist James Hutton is that "the present is the key to the past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now."[25]​.

• - The principle of intrusive relationships refers to transversal intrusions. In geology, when an igneous intrusion passes through a sedimentary rock formation, it can be determined that the igneous intrusion is younger than the sedimentary rock. Different types of intrusions include strains, laccoliths, batholiths, sills and dikes.

• - The principle of transversal relationships refers to the formation of faults and the age of the sequences through which they cut. The faults are younger than the rocks they cut; Consequently, if a fault is found that penetrates some formations but not those above it, then the formations that were cut are older than the fault, and those that are not cut must be younger than the fault. Finding the key platform in these situations can help determine whether the fault is a normal fault or a thrust fault.[26]​.

• - The principle of inclusions and components states that, with sedimentary rocks, if inclusions (or clasts) are found in a formation, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for gravel from an older formation to be broken up and included in a newer layer. A similar situation with igneous rocks occurs when xenoliths are found. These foreign bodies are collected as magma or lava flows, and incorporated and then cooled in the matrix. As a result, xenoliths are older than the rock that contains them.

• - The original horizontality principle states that sediment deposition occurs as essentially horizontal beds. Observation of modern marine and non-marine sediments in a wide variety of environments supports this generalization (although cross-strata are inclined, the general orientation of cross-strata units is horizontal).[26]​.

• - The principle of superposition states that a layer of sedimentary rock in a tectonically unaltered sequence is younger than the one below it and older than the one above it. Logically, a younger layer cannot slide beneath a previously deposited layer. This principle allows sedimentary layers to be viewed as a form of vertical timeline, a partial or complete record of the time from the deposition of the lowest layer to the deposition of the highest bed.[26]​.

• - The principle of faunal succession is based on the appearance of fossils in sedimentary rocks. As organisms exist during the same period throughout the world, their presence or (sometimes) absence provides a relative age of the formations where they appear. Based on principles that William Smith established almost one hundred years before the publication of Charles Darwin's theory of evolution, the principles of succession were developed independently of evolutionary thinking. The principle becomes quite complex, however, given the uncertainties of fossilization, the location of fossil types due to lateral changes in habitat (facies change in sedimentary strata) and that not all fossils were formed globally at the same time.[27]​.

absolute dating

Geologists also use methods to determine the absolute age of rock samples and geological events. These dates are useful on their own and can also be used in conjunction with relative dating methods or to calibrate relative methods.[28]​.

At the turn of the century, the advancement of geological science was facilitated by the ability to obtain precise absolute dates of geological events using radioactive isotopes and other methods. This changed the understanding of geological time. Previously, geologists could only use fossils and stratigraphic correlation to date sections of rock to each other. With isotopic dates, it was possible to assign absolute ages to rock units, and these absolute dates could be applied to fossil sequences in which datable material was present, converting old relative ages into new absolute ages.

For many geological applications, isotope ratios of radioactive elements are measured in minerals giving the amount of time that has passed since a rock passed its particular closure temperature, the point at which different radiometric isotopes stop diffusing in and out of the crystal lattice.[29][30]These are used in geochronological and thermochronological studies. Common methods include uranium-lead dating, potassium-argon dating, argon-argon dating, and uranium-thorium dating. These methods are used for a variety of applications. Dating of lava and volcanic ash layers found within a stratigraphic sequence can provide absolute age data for sedimentary rock units that do not contain radioactive isotopes and calibrate relative dating techniques. These methods can also be used to determine the emplacement ages of plutons. Thermochemical techniques can be used to determine temperature profiles within the crust, the elevation of mountain ranges, and paleo-topography.

Fractionation of lanthanide series elements is used to calculate ages since rocks were removed from the mantle.

Other methods are used for more recent events. Optically stimulated luminescence and cosmogenic radionuclide dating are used to date surfaces and/or erosion rates. Dendrochronology can also be used for landscape dating. Radiocarbon dating is used for geologically young materials containing organic carbon.

plate tectonics

In the 1960s it was discovered that the Earth's lithosphere, which includes the crust "Crust (geology)") and the rigid upper part of the upper mantle, is separated into tectonic plates that move through the deformable plastic solid upper mantle "Plasticity (mechanics of solids)"), which is called the asthenosphere. This theory is supported by several types of observations, such as seafloor spreading[31][32]​ and the global distribution of mountainous terrain and seismicity.

There is an intimate coupling between plate motion at the surface and mantle convection (i.e., heat transfer caused by the slow movement of ductile rock in the mantle). Thus, oceanic plates and adjacent mantle convection currents always move in the same direction, because the oceanic lithosphere is actually the rigid upper thermal boundary layer of the convective mantle. This coupling between the rigid plates moving on the Earth's surface and the convective mantle is called plate tectonics.

The development of plate tectonics has provided a physical basis for many observations of the solid Earth. Long linear regions of geological features are explained as plate boundaries.[33]​.

For example:.

• - Mid-ocean ridges, elevated regions on the seafloor where hydrothermal vents and volcanoes exist, are seen as divergent edges, where two plates move apart.

• - Volcanic arcs and earthquakes are considered convergent boundaries, in which one plate subducts, or moves, under another.

Transform edges, such as the San Andreas fault system, gave rise to powerful widespread earthquakes. Plate tectonics has also provided a mechanism for Alfred Wegener's theory of continental drift,[34] in which continents move across the Earth's surface over geological time. They also provided a driving force for crustal deformation, and a new setting for observations of structural geology. The power of the theory of plate tectonics lies in its ability to combine all of these observations into a single theory of how the lithosphere moves over the convective mantle.

Earth Structure

Advances in seismology, numerical modeling and mineralogy and crystallography at high temperatures and pressures allow us to understand the internal composition and structure of the Earth.

Seismologists can use the arrival times of seismic waves to obtain images of the Earth's interior. The first advances in this field showed the existence of a liquid outer core (where shear waves" could not propagate) and a solid, dense inner core. These advances led to the development of a stratified model of the Earth, with a crust "Crust (geology)") and a lithosphere on top, the mantle "Mantle (geology)") below (separated in its interior by seismic discontinuities at 410 and 660 kilometers), and the outer core and the inner core below. More recently, seismologists have been able to create detailed images of wave speeds inside the Earth, in the same way that a doctor images a body in a tomography scan. These images have allowed a much more detailed view of the Earth's interior and have replaced the simplified layer model with a much more dynamic model.

Mineralogists have been able to use pressure and temperature data from seismic and modeling studies along with knowledge of the Earth's elemental composition to reproduce these conditions in experimental settings and measure changes in crystal structure. These studies explain the chemical changes associated with the main seismic discontinuities of the mantle and show the crystalline structures expected in the Earth's inner core.

Regional geology

Regional geology") is the branch of geology that studies the geological configuration of each continent, country, region or specific areas of the Earth.

Geology includes different sciences or disciplines, which make up university or professional educational training plans. Due to the great diversity of disciplines or geological sciences, these are grouped into different independent teaching units, where a better modular organization of the teaching and research of Geology on the different sciences it comprises is carried out. One of the general structures in which these departments are composed is:

• - Department of Crystallography and Mineralogy (includes gem mineralogy).

• - Department of Stratigraphy and Sedimentology.

• - Dept. of Geodynamics. Which is subdivided, in turn, into:

• Internal Geodynamics (structural geology, historical geology, tectonics; geophysics and seismology)

• External Geodynamics (geomorphology, hydrogeology and geotechnics; economic and petroleum geology).

• - Department of Paleontology.

• - Dept. of Petrology and Geochemistry (includes volcanology and planetary geology).

A geologist is a specialist and professional in the study, observation or experimentation related to the Earth, its composition, structure, dynamics, origin and evolution. In your professional work you must apply the principles of geoethics.

A geologist stands out for having the following skills:

• - Carry out petrographic studies and chemical analyzes to determine the origin, composition and evolution of rocks.

• - Establishes the stratigraphy of a region and performs structural analysis to establish the genetic order of the geological units in a region and to define both macro-structures and microstructures, in order to describe the tectonic evolution of said region.

• - Prepares geomorphology, morphometry and morphotectonics to establish the relief forms of a region, and the factors that formed them that allow them to identify the areas of greatest energy, basin limits, erodibility and develop their professional activity with a sense of service to society and with attachment to their quality and professional attachment.

• - Carry out geochemical and geophysical studies to determine both the content of ionic species in surface, underground and hydrothermal waters, as well as the chemical composition of rocks, and their applications in the geochemical evolution of natural waters and in mineral prospecting. Determines the physical properties of the Earth's crust, the professional remains critical of scientific progress and the development of its environment.

• - Designs mineral prospecting and exploration studies, performs analysis to determine areas with potential mineral deposits, and quantification. The techniques and parameter determinations are: samples taken, km² explored, meters drilled, drilling efficiency, grade of the samples tested and unit costs.

• - Prepares studies of groundwater and water quality, defines the economic process or processes necessary to define the deposits, extract and manage subsoil water resources with respect for oneself, others and the environment.

• - Designs geotechnical studies to know the physical properties of soils and rocks to determine risk areas or problems of subsidence and active faulting.

• - Carry out the planning, design and development of geological projects to plan, design and develop general and applied geology studies, which will solve specific problems or perform specific tasks within a unitary process or operation.[69]​.

• - Earth Sciences.

• - Geological time scale.

• - Plate tectonics.

• - Annex: Common definitions in geology.

• - Compton, Robert R. (1985). Geology in the field. New York: Wiley. ISBN 978-0-471-82902-7.

• - F. Lutgens, E. Tarbuck, D. Tasa. Essentials of Geology 13th Edition. (2017) 608 pages. ISBN 0134446623, ISBN 978-0134446622.

• - Stephen Marshak. Essentials of Geology Sixth Edition. 720 pages (2019) ISBN 0393667529, ISBN 9780393667523.

• - Wikimedia Commons hosts a multimedia category on Geology.

• - Wikiquote hosts famous quotes from or about Geology.

• - Wikinews has news related to Geology.

• - International Union of Geological Sciences - International Union of Geological Sciences (IUGS).

• - Geological and Mining Institute of Spain (IGME).

• - Geological Studies, Magazine of the National Museum of Natural Sciences (Spain) "National Museum of Natural Sciences (Spain)"), CSIC.

• - Geology Dictionary (Spanish/English) - Mineriaenlinea.com.

• - Colombian Institute of Geology and Mining (INGEOMINAS).

• - EARTH Earth Sciences Thematic Network.

• - Magazine of the Argentine Geological Association.

• - Geology, Mining and Petroleum of Peru.

• - Geology Portal in Spanish.

• - National University of Colombia. Geology Manual for Engineers (2003) Archived August 21, 2016 at the Wayback Machine.