Index Fossils and Their Significance
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Questions and Answers

What is the primary purpose of index fossils?

  • To identify the nutritional habits of ancient organisms
  • To classify living species of today
  • To determine the age of geological formations (correct)
  • To describe the physical characteristics of rocks

    • Which characteristic is NOT true for index fossils?

  • They are limited in time span
  • They are abundant and easily identifiable
  • They have a long geologic range (correct)
  • They have a wide geographic distribution

    • Which fossil is an example of a Jurassic index fossil?

  • _Billingsella corrugata_
  • _Venericardia planicosta_
  • _Perisphinctes tiziani_ (correct)
  • _Cactocrinus multibrachiatus_

    • What describes the term 'geologic range'?

    <p>The length of time an organism exists on earth (A)</p> Signup and view all the answers

    Which of these is NOT an index fossil group mentioned?

    <p>Pelagic fishes (A)</p> Signup and view all the answers

    What common characteristic do ammonites and gastropods share?

    <p>Both are classified as molluscs (A)</p> Signup and view all the answers

    Which index fossil is classified from the Carboniferous period?

    <p><em>Dictyoclostus americanus</em> (D)</p> Signup and view all the answers

    What makes a fossil an 'index fossil'?

    <p>It is easily recognizable and has a limited time span (A)</p> Signup and view all the answers

    Flashcards

    Index Fossil

    A fossil widely distributed, common, and limited in time, used to determine ages of rock layers and relate them.

    Geologic range

    The total time span an organism existed on Earth.

    Fossil

    A preserved trace of a plant or animal from the past, found in rock layers.

    Index fossil uses

    To match rock layers across large distances and date rock strata.

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    Index fossil criteria

    Abundant, easily identifiable, wide geographic spread, and short geologic range.

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    Ammonite

    A type of mollusk with a coiled shell, often used as an index fossil.

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    Brachiopod

    A marine invertebrate with two shells.

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    Trace fossil

    Evidence of an organism's existence (e.g footprints), not the organism itself.

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    Study Notes

    Index Fossils

    • Index fossils are widely distributed fossils with a limited time span.
    • They are used to determine the age of rocks and establish relationships between rock layers.
    • "Fossil" literally means anything dug from the earth.
    • Fossils are remnants of plants or animals, or related items, providing evidence of past life.
    • Fossil taxa are unique sets of fossils that characterize rock layers.
    • William Smith, a British engineer, recognised the use of fossils to correlate rock layers across vast distances.
    • Index fossils, or guide fossils, are restricted to specific geologic horizons.
    • Some index fossils represent animal groups.

    Animal Index Fossils

    • Ammonites: Molluscs with coiled shells; Perisphinctes tiziani (Jurassic) and Trophites subbullatus (Triassic) are examples.
    • Gastropods: Molluscs with asymmetrical, spirally-twisted shells; Nerinea trinodosa (Jurassic) is an example.
    • Pelecypods: Bivalve shelled molluscs with a tongue-shaped foot; Venericardia planicosta (Tertiary) is an example.
    • Brachiopods: Bilaterally symmetrical animals with bivalve shells; Billingsella corrugata (Cambrian) and Dictyoclostus americanus (Carboniferous) are examples.
    • Crinoids: Marine invertebrates with cup-shaped bodies and feathery tentacles; Cactocrinus multibrachiatus (Carboniferous) is an example.
    • Trilobites: Extinct marine arthropods with three lobes; Paradoxides pinus and Bathyurus extans are examples from the Cambrian and Ordovician periods, respectively.

    Characteristics of Index Fossils

    • An organism must have lived for only a short period of Earth's history.
    • Numerous fossils of the organism must be found in various rock layers.
    • The fossils must be found over a wide geographical area.
    • The organism's characteristics must be unique.

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    Index Fossils PDF

    Description

    Explore the fascinating world of index fossils and learn how they help determine the age of rocks and their relationships. This quiz covers key concepts about index fossils, including notable examples like ammonites and gastropods. Understand their role in geology and the history of life on Earth.

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