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Geology

University

Introduction to the Degree in Geology. Source: Wikipedia (CC BY-SA 4.0).

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Fundamentals of Geology and Geological Materials

  • Geology: the study of the composition, structure, and evolution of the Earth.
  • Applications: mining, hydrocarbons, hydrogeology, geotechnics, and disaster prevention.
  • Branches: geophysics, tectonics, stratigraphy, geomorphology, petrology, soil science (edaphology), among others.
  • Milestones: mining (18th century), paleontology (19th century), plate tectonics (1960s).
  • Minerals: natural compounds with a homogeneous chemical composition and an ordered atomic structure.
  • Mineral testing: luster, color, streak, hardness, fracture pattern (fracture/cleavage), specific gravity, effervescence, magnetism, and taste.
  • Rocks: natural solid masses; types: igneous (melting), sedimentary (lithification), and metamorphic (heat/pressure).
  • Rock cycle: the process of transformation between the three main types.
  • Organic matter: primarily associated with sedimentary rocks.
  • Quaternary Geology: the study of non-lithified materials (surface deposits).
  • Magma: the original source of igneous rocks; volcanology studies its active flow.

Geological milestones and principles of relative dating

  • Formation of the solar system: 4,600 million years
  • Formation of the Earth: 4.54 Ga
  • First evidence of life: c. 4 Ga
  • Onset of photosynthesis: c. 3.5 Ga
  • Oxygenated atmosphere and 1st global glaciation: c. 2.3 Ga
  • Cambrian explosion and beginning of the Paleozoic: 542± 0.3 Ma
  • First terrestrial vertebrates: c. 380 Ma
  • Permian-Triassic extinction (end of Paleozoic): 250 Ma (90% of terrestrial fauna dies)
  • Cretaceous-Tertiary extinction (end of Mesozoic): 65 Ma
  • Appearance of hominids: c. 7 Ma
  • Appearance of Australopithecus: 3.9 Ma
  • First modern Homo sapiens: 200 ka
  • Uniformitarianism: current processes are the same as those in the past
  • Intrusive relationships: the intrusion is younger than the host rock
  • Cross-cutting relationships: the fault is younger than the rocks it cuts
  • Inclusions: clasts and xenoliths are older than the matrix
  • Original horizontality: sediments are deposited horizontally
  • Superposition: lower layers are older than the upper layers
  • Faunal succession: fossils indicate the relative age of the formations

Geological dating methods and plate tectonics theory

  • Absolute dating: allows for the calibration of relative dating and the assignment of precise dates to rock units.
  • Closure temperature: the point at which isotopes cease to diffuse through the crystal lattice.
  • Common isotopic methods: uranium-lead, potassium-argon, argon-argon, and uranium-thorium.
  • Lava/ash dating: used to calibrate sedimentary units lacking radioisotopes.
  • Thermo-chemical techniques: determine temperature profiles, elevation, and paleotopography.
  • Lanthanide fractionation: calculates the time since rocks were removed from the mantle.
  • Luminescence and cosmogenic radionuclides: date surfaces and erosion rates.
  • Dendrochronology: used for dating landscapes.
  • Radiocarbon dating: only for young materials containing organic carbon.
  • Lithosphere: the crust and the rigid upper part of the upper mantle.
  • Asthenosphere: the solid, plastic, and deformable upper mantle.
  • Mantle convection: heat transfer through the movement of ductile rock.
  • Divergent boundaries: mid-ocean ridges (plate separation).
  • Convergent boundaries: volcanic arcs and subduction zones.
  • Transform boundaries: faults that generate earthquakes (e.g., San Andreas Fault).
  • Continental drift: a mechanism explained by plate tectonics.

Internal structure of the Earth, branches of geology, and the professional profile of a geologist

  • Outer core: liquid (does not allow shear waves)
  • Inner core: solid and dense
  • Mantle seismic discontinuities: 410 and 660 km
  • Regional geology: study of the configuration of continents, countries, or regions
  • Internal Geodynamics: includes structural, historical, tectonic, geophysical, and seismological geology
  • External Geodynamics: includes geomorphology, hydrogeology, geotechnics, economic geology, and petroleum geology
  • Mineral exploration: key parameters are km² explored, meters drilled, efficiency, sample grade, and costs
  • Geotechnics: study of the physical properties of soils and rocks to detect risks of subsidence or active faulting
  • Geologist: a professional who applies geoethics in the study of terrestrial dynamics and evolution

References and resources on Geology

  • Related topics: Earth Sciences, geological time scale, and plate tectonics
  • Key work: Oldroyd (2004) on James Hutton's Theory of the Earth
  • Reference manuals: Lutgens, Tarbuck, and Tasa (2017) and Marshak (2019)
  • Reference institutions: IUGS, IGME, and INGEOMINAS
  • Digital resources: Wikimedia Commons, Wikinoticias, and Dictionary of Geology

Flashcard preview (6 of 25)

  1. 01

    In geology, what defines a mineral?

    A natural element or compound with a defined homogeneous chemical composition and an ordered atomic structure.

  2. 02

    In the study of minerals, what is luster?

    The quality of light reflected from the surface.

  3. 03

    Difference between fracture and cleavage in a mineral's breakage pattern:

    Fracture: uneven surfaces; Cleavage: parallel planes very closely spaced.

  4. 04

    What type of rock is formed when a solid mass solidifies or crystallizes from a melt (magma or lava)?

    Igneous rock.

  5. 05

    What is the original non-lithified source of all igneous rocks?

    Magma.

  6. 06

    Time milestone: When did the formation of the Earth occur?

    4.54 Ga

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