Sevier Orogeny and Continental Drift Overview
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Questions and Answers

What primary observation led early mapmakers to suggest that continents might have once been joined together?

  • The alignment of mountain ranges on opposite sides of the oceans.
  • The patterns of ocean currents and prevailing winds around continents.
  • The distribution of specific minerals across different continents.
  • The close fit of continental coastlines, like a jigsaw puzzle. (correct)

    • Which of these geological features provides evidence supporting the theory of plate tectonics?

  • The consistent age of rocks found on different continental landmasses.
  • The presence of shallow ocean limestone at the summits of mountains. (correct)
  • The uniform distribution of sedimentary rocks across continents.
  • The random distribution of fossils across various geographical locations.

    • What was the crucial difference in Wegener's approach to continental drift compared to his predecessors like Antonio Snider-Pellegrini?

  • Wegener compiled and synthesized a large amount of diverse data in one comprehensive theory. (correct)
  • Wegener dismissed the possibility of trans-oceanic land bridges for species dispersal.
  • Wegener only considered evidence from the coastlines of Africa and South America.
  • Wegener focused solely on geological evidence, ignoring biological data.

    • What was a common objection to the theory of continental drift, before the concept of plate tectonics was widely accepted?

    <p>The existence of trans-oceanic land bridges allowing species migration. (B)</p> Signup and view all the answers

    Why is plate tectonics considered revolutionary in the field of geology?

    <p>It provided a unified explanation for various geological phenomena. (A)</p> Signup and view all the answers

    What key observation led Inge Lehmann to hypothesize the existence of a solid inner core?

    <p>Analysis of seismic wave data. (C)</p> Signup and view all the answers

    Why is Earth's liquid outer core important for sustaining life on Earth?

    <p>It shields the Earth from harmful solar radiation by generating the magnetic field. (A)</p> Signup and view all the answers

    What is the primary factor that allows the inner core to remain solid despite its high temperature?

    <p>The immense pressure exerted by the overlying layers. (C)</p> Signup and view all the answers

    What is the main difference between passive and active tectonic margins?

    <p>Active margins involve relative movement between tectonic plates, whereas passive margins do not. (C)</p> Signup and view all the answers

    What occurs in the mantle wedge during subduction that leads to the formation of volcanic arcs?

    <p>Volatiles from the subducting plate lower the melting point of the mantle material, creating magma. (C)</p> Signup and view all the answers

    What was a significant flaw in Alfred Wegener's continental drift hypothesis?

    <p>The absence of a credible mechanism to explain how continents moved. (B)</p> Signup and view all the answers

    What evidence from ocean floor mapping supported the theory of plate tectonics?

    <p>The identification of the Mid-Atlantic Ridge, a basaltic mountain range, with unique rock chemistry and dimensions. (D)</p> Signup and view all the answers

    Which of the following best describes the significance of magnetic anomalies found on the ocean floor?

    <p>They revealed a pattern of symmetrical rows with alternating magnetic poles, supporting seafloor spreading. (C)</p> Signup and view all the answers

    What is the study of paleomagnetism and how did it support the theory of plate tectonics?

    <p>The study of magnetic fields frozen within rocks, revealing continental movement by comparing the alignment of magnetic north in rocks to the earth's current magnetic north. (B)</p> Signup and view all the answers

    What are Wadati-Benioff zones and what do they indicate?

    <p>Deep earthquake zones that trace the shapes of oceanic plates sinking into the mantle. (C)</p> Signup and view all the answers

    Which of the following statements accurately describes the Mohorovičić Discontinuity (Moho)?

    <p>It is characterized by a large increase in seismic velocity, marking the chemical boundary between the crust and the mantle. (D)</p> Signup and view all the answers

    What are the primary sources of information scientists use to understand the composition and characteristics of the Earth's mantle?

    <p>Analysis of seismic wave data, study of ophiolites, and examination of xenoliths. (C)</p> Signup and view all the answers

    How does the physical behavior of the asthenosphere contribute to plate tectonic processes?

    <p>Its mechanically weak and mobile nature allows it to flow due to convection currents, facilitating the movement of lithospheric plates above. (D)</p> Signup and view all the answers

    Which of the following comparisons accurately describes the differences between oceanic and continental lithosphere?

    <p>Oceanic lithosphere is thinner and more rigid compared to continental lithosphere. (A)</p> Signup and view all the answers

    What is the primary basis for differentiating the Earth's layers based on chemical composition?

    <p>The layers are differentiated by the elements and compounds that dominate each layer, influenced by temperature and pressure. (A)</p> Signup and view all the answers

    Flashcards

    Outer Core

    The only completely liquid layer of the Earth, 2,300 km thick.

    Inner Core

    The solid innermost layer of the Earth about 1,220 km thick, despite high temperatures.

    Subduction Zone

    Where one tectonic plate moves beneath another, often forming trenches.

    Active Margin

    A tectonic plate boundary where oceanic and continental plates meet and move.

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    Volcanic Arc

    Curved chains of volcanoes formed at convergent boundaries from subduction.

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    Plate Tectonics

    Theory explaining the movement of Earth's outer layers and its geological activities.

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    Paradigm Shift

    A fundamental change in the underlying assumptions or methodologies within a particular field.

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    Continental Drift

    Theory that continents have moved over geological time from a connected supercontinent.

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    Wegener's Evidence

    Used geological and fossil data to support the theory of continental drift.

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    On the Origin of Species

    Darwin's 1859 book that proposed evolution through natural selection.

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    Seafloor Spreading

    The process by which new oceanic crust is formed at mid-ocean ridges and pushed away.

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    Paleomagnetism

    Study of magnetic fields in rocks, indicating historical positions of continents.

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    Wadati-Benioff Zones

    Areas of deep earthquakes linked to tectonic plate interactions like subduction.

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    Tuzo Wilson

    First scientist to propose the tectonic plate model.

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    Crust

    Outermost layer of the Earth, consisting of continental and oceanic types.

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    Mohorovičić Discontinuity (Moho)

    Boundary between Earth's crust and mantle where seismic wave speed changes.

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    Lithosphere

    Outermost physical layer of the Earth, broken into tectonic plates.

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    Asthenosphere

    Layer below the lithosphere, characterized by weak, flowing behavior due to heat.

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    Study Notes

    Sevier Orogeny and Plate Tectonics

    • A layer of shallow ocean limestone was brought to the top of a mountain by the convergent forces of the Sevier Orogeny near Sun River Canyon, Montana.
    • "Revolution" in science refers to significant paradigm shifts that force scientists to re-evaluate their understanding, like Darwin's evolution, Mendel's genetics, Watson-Crick-Franklin DNA model, and Einstein's relativity, impacting various fields.
    • Plate tectonics is a revolutionary geological theory explaining Earth's dynamic surface, attributing earthquakes, mountains, and volcanoes to the movement of massive sections of the Earth's outer layers.

    Wegener's Continental Drift Hypothesis

    • Wegener synthesized evidence from similar rocks, mountains, fossils, and glacial formations across oceans, proposing continents once formed a single landmass.
    • Continental coastlines had a jigsaw-like fit (e.g., South America and Africa).
    • Evidence included fossils of Mesosaurus and Lystrosaurus found on separate continents, implying land bridges couldn't explain the trans-oceanic distributions of land-dwelling creatures.
    • Glacial deposits in warm areas and tropical plant fossils in frozen regions were evidence against land bridges.
    • Wegener couldn't explain the mechanism of continental drift, a critical gap in his theory that hindered acceptance.

    Evidence supporting Plate Tectonics

    • Ocean floor mapping revealed the Mid-Atlantic Ridge, a basaltic mountain range.
    • Harry Hess proposed seafloor spreading, a process where new oceanic crust forms at mid-ocean ridges.
    • Seafloor sediment thickness provided evidence against stationary ocean floors, and supported the concept of seafloor spreading and plate movement.
    • Paleomagnetism (study of magnetic fields in rocks) provided crucial evidence for plate motion with symmetrical magnetic patterns on either side of mid-ocean ridges, revealing sea floor spreading.
    • Earthquake epicenters followed the shapes of oceanic plates sinking into the mantle, forming Wadati-Benioff zones. Linking earthquakes to plate motion.

    Layers of the Earth: Chemical and Physical

    • The Earth has three major chemical layers: crust, mantle, and core. The crust has continental and oceanic forms.
    • Seismic waves provide understanding of the Earth's interior and have been used to identify the Mohorovičić Discontinuity (Moho), the boundary between the crust and the mantle.
    • Physical layers include lithosphere, asthenosphere, mesosphere, outer core, and inner core.
    • Lithosphere is broken into plates, with plate boundaries actively shaping Earth's surface.
    • Asthenosphere is the mechanically weak layer below the lithosphere that allows for plate movement.

    Types of Plate Boundaries

    • Plate boundaries are categorized as convergent, divergent, and transform.
    • Convergent boundaries (destructive): Plates move towards each other, leading to subduction (one plate descending beneath another) or collision (both plates have similar densities, causing uplift).
    • Divergent boundaries (constructive): Plates move apart, creating new crust, like at mid-ocean ridges or rift valleys. This can be narrow, like the East African Rift, or broad, like the Basin and Range region of the western United States.
    • Transform boundaries (conservative): Plates slide past each other, creating earthquakes. A notable example is the San Andreas Fault.

    The Wilson Cycle

    • The Wilson Cycle describes the continuous opening, closing, and reopening of ocean basins, generating supercontinents like Pangea.
    • Driving mechanisms of plate movement include ridge push, slab pull, and gravitational sliding.
    • Hotspots are fixed points of volcanic activity unrelated to plate boundaries, creating island chains as the plate moves over them, like the Hawaiian Islands.

    Additional Concepts

    • Active margins are locations where oceanic and continental plates meet with significant movement, leading to mountain building and earthquakes. Passive margins form at the juncture of plates where one plate is made up of both continental and oceanic lithosphere.
    • Subduction processes often lead to the formation of volcanic arcs, which are curved chains of volcanoes.
    • Collision zones result in the formation of tall, non-volcanic mountains, high earthquake activity, and little volcanism.

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    Description

    Explore the geological concepts behind the Sevier Orogeny and Wegener's Continental Drift Hypothesis. This quiz covers significant scientific revolutions and the forces that shape Earth's structure, highlighting key evidence from mountain formations to fossil discoveries.

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