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Deformation of the Crust

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Plate Tectonics

Plate Tectonics

  • It is a theory that describes the structure of the Earth’s crust.
  • It states that the Earth’s crust is divided into large pieces of rigid lithospheric plates.
  • These plates float over molten hot material over the asthenosphere.
    • This allows convection currents from the mantle to move the plates.
  • In the boundary between two plates are said to be a place where most igneous and metamorphic processes occur.

Plate Boundaries

Plate Boundary

  • It is a place where two different plates meet.
  • According to the Plate Tectonic theory, most geological features and rock processes form on the regions where plates meet.
  • There are three different types of plate boundaries: divergent, convergent and transform/lateral

Divergent Plate Boundary

  • A plate boundary where two plates move away from one another.

Convergent Plate Boundary

  • A plate boundary where two plates move toward each other.

Lateral/Transform Plate Boundary

  • A plate boundary where two plates move past one another.

  • There are two types of lateral or transform plate boundaries: left lateral (sinistral) or right lateral (dextral)

Rock Dating

Rock Dating

  • It is a process of finding the age at which a rock started to form.
  • There are two types of rock dating methods: relative dating and absolute dating.

Relative Dating

  • It is a process of arranging geological events based of the sequence of rocks.
  • Here, the age of a rock is determined by comparing it to an another rock with a known age.
  • This type of rock dating can be hugely inaccurate.
    • This is because they are made from educated guesses
  • The process of relative dating is based upon the three Steno’s Laws.
    • Law of Original Horizontality
      • It states that some sediments layer themselves horizontally due to the force of gravity.
      • When deformation arises in horizontally layered sediments, this is due to geological processes such as faulting, tectonic plate movement, or volcanic activity.
      • The amount of deformation from the horizontal layering of the rock may indicate how old a rock is.
    • Law of Superposition
      • It states that for an undisturbed rock sequence, the oldest rocks lie at the very bottom, while the newer sediments form at the top.
      • This is because it is not possible for sediments or rocks to slip beneath a layer already deposited.
    • Law of Cross-cutting Relationships
      • It states that a geologic feature that cuts an another geologic feature is the youngest between the two.

Absolute Dating

  • It uses radioactivity to determine the exact age of a rock.
  • During the formation of the rock, some radioactive atoms may get trapped inside as it cools.
    • When certain radioactive elements decay, they also leave trace elements, known as decay pro that are a byproduct of that process.
    • The time of the decay process is something that geologists can accurately calculate.
    • The percentage of radioactive atoms decayed into trace elements determines the age of the rock.
  • Geologists use these three types of radiometric dating that can be applied to accurately determine a rock’ age.
    • Radiocarbon Dating
      • most often used in fossils and organic rocks
      • can be used on rocks between 100-50,000 years.
      • plants naturally contain a form of radioactive carbon called .
        • animals also get radioactive carbon by feeding on to plants.
        • as plants and animals die, they stop exchanging carbon in the environment.
        • eventually, the amount of carbon decreases as decays.
        • the amount of remaining atoms remaining determines the age of the rock
    • (Potassium-Argon) Dating
      • uses the decay product of radioactive potassium to find the age of a rock.
      • it can be used to determine the age from years to over a billion years old
      • potassium is a common element in many minerals
        • one isotope of potassium, decay into atoms
        • these atoms can easily leave liquid, molten rock.
          • but, as the rock cools, atoms begin to accumulate inside.
        • the ratio of accumulated versus the remaining determines the age of the rock.
    • (Uranium-Lead) Dating
      • uses uranium and its decay of lead to find the age of the rock
      • the oldest and most refined radiometric dating schemes to date.
      • when zircon crystals form, they accept uranium and thorium atoms inside, but not lead atoms.
        • therefore, any presence of lead inside the rock must come from the decay of uranium.
        • this can be used to accurately determine the age of the rock
      • it utilizes two types of decay chains:
        • , which can date rocks up to billion years
        • , which can date rocks up to million years.

Geologic Time Scales

Geological Time Scale

  • also known as geologic time scale
  • it is a representation of time based on the geologic record of the Earth
  • through the invention of rock dating methods, geologists were able to determine the events in Earth’s history by examining rocks and fossils.

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