Geologic Time Scale Overview
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Questions and Answers

What is the largest time unit in the geologic time scale?

  • Epoch
  • Era
  • Period
  • Eon (correct)

    • Which principle states that sedimentary rocks are deposited in horizontal layers?

  • Superposition
  • Lateral Continuity
  • Original Horizontality (correct)
  • Cross-Cutting

    • During which eon did fossil evidence suggest that simple life-forms appeared?

  • Archean (correct)
  • Proterozoic
  • Hadean
  • Phanerozoic

    • What does superposition state regarding rock layers?

    <p>The oldest rocks are at the bottom. (D)</p> Signup and view all the answers

    What is the main focus of relative-age dating?

    <p>Placing rock layers in a sequence without numbers. (B)</p> Signup and view all the answers

    Which principle indicates that an intrusion is younger than the rock it cuts across?

    <p>Cross-Cutting Relationships (C)</p> Signup and view all the answers

    How long do epochs generally last?

    <p>Hundreds of thousands to millions of years (C)</p> Signup and view all the answers

    Which concept suggests that layers of rock extend until the environment changes?

    <p>Lateral Continuity (B)</p> Signup and view all the answers

    Flashcards

    What are fossils?

    Fossils are the preserved remains, traces, or imprints of ancient organisms, often found embedded in rocks. Studying rock layers and the fossils within them helps geologists unravel Earth's history and understand past environments.

    What is the geologic time scale?

    The geologic time scale is a visual timeline of Earth's history, spanning from its formation 4.6 billion years ago to the present.

    What is an eon?

    An eon is the largest unit of geologic time. The Precambrian eon encompasses the first 90% of Earth's history and witnessed the formation of Earth and the emergence of early life.

    What are eras?

    Eras are the next largest division of geologic time, smaller than eons. They typically last tens to hundreds of millions of years.

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    What are periods?

    Periods are subdivisions of eras, smaller than eras. They typically last tens of millions of years.

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    What are epochs?

    Epochs, the smallest unit of geologic time, are subdivisions of periods and can last hundreds of thousands to millions of years. They help us understand finer details within periods.

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    What is relative-age dating?

    Relative-age dating is a method used to determine the sequence of geologic events without using numerical ages. It relies on principles like superposition and cross-cutting relationships.

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    What is the principle of original horizontality?

    The principle of original horizontality states that sedimentary rocks are originally deposited in horizontal or nearly horizontal layers.

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    Study Notes

    Organizing Time

    • Fossils are remains, traces, or imprints of ancient organisms found in rocks.
    • Studying rock layers and fossils helps geologists understand Earth's history and past environments.
    • The geologic time scale is a graphic representation of Earth's history from 4.6 billion years ago to the present.

    Geologic Time Scale

    • An eon is the largest unit of time.
    • The three earliest eons (Precambrian) make up 90% of geologic time.
    • During the Precambrian, Earth formed and became hospitable to modern life.
    • Simple life-forms appeared during the Archean Eon.

    Eras

    • Eras are the next largest units of time, typically tens to hundreds of millions of years in duration.
    • Eras are made up of eons.

    Periods

    • Eras are divided into periods.
    • Periods typically last tens of millions of years.

    Epochs

    • Periods are divided into epochs.
    • Epochs usually last hundreds of thousands to millions of years.

    Relative Age Dating

    • Relative-age dating places rock layers and geologic events in the order they formed or occurred.
    • No dates or numbers are used.

    Principles of Relative Dating

    • Original Horizontality: Sedimentary rocks are deposited in horizontal layers.
    • Superposition: In undisturbed rock sequences, the oldest rocks are on the bottom, and layers get progressively younger upward.
    • Lateral Continuity: Layers of rock extend in all directions until the environment changes.
    • Cross-Cutting Relationships: An intrusion or fault is younger than the rock it cuts across.
    • Inclusions: Rock fragments (inclusions) within a layer are older than the layer containing them.

    Correlation

    • Correlation matches rock outcrops in different locations.
    • A key bed is a rock layer that serves as a time marker.
    • Index fossils are easily recognized, abundant, and widely distributed fossils.
    • Index fossils can be used to correlate rock layers of the same age but not necessarily the same rock type.

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    Related Documents

    Rock Record and Relative Dating Notes PDF

    Description

    This quiz covers the essential concepts of the geologic time scale, including the definitions and relationships between eons, eras, periods, and epochs. It also explores the importance of fossils and rock layers in understanding Earth's history. Perfect for students aiming to deepen their knowledge of geology.

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