SEAFLOOR SPREADING AND MAGNETIC REVERSAL | SCIENCE 10 - Week 8 Part II

00:07:53
https://www.youtube.com/watch?v=Fr44e9BBX7k

Summary

TLDRThe video explores the evidence supporting plate tectonics, particularly the seafloor spreading theory and magnetic reversal. Initially, continental drift theory proposed by Wegener suggested continents were once a unified supercontinent, Pangaea. However, lacking an explanation for the mechanism of movement, it wasn't widely accepted. Later discoveries in the 1950s and 1960s revealed mid-ocean ridges and led to the seafloor spreading theory by Harry Hess and Robert Dietz. This theory posits that new oceanic crust forms at these ridges as magma rises, then cools and spreads the seafloor apart, giving rise to new bodies of water. Evidence supporting this includes younger rocks closer to ridges and symmetric magnetic stripes indicating magnetic reversals on the seafloor, which demonstrate a historical record of these shifts. The phenomenon of magnetic reversal happens when Earth's magnetic poles flip, further supporting the spreading of the seafloor. This process helps explain continental drift and current ocean expansion or shrinking patterns.

Takeaways

  • 🌍 Continental drift theory suggests Pangaea split into continents.
  • 🧭 Seafloor spreading theory explains new ocean crust formation.
  • 🗻 Mid-ocean ridges are sites where new seafloor is created.
  • 🔄 Magnetic reversal shows Earth's poles switching over time.
  • 🧲 Magnetic stripes in oceanic rocks indicate past pole reversals.
  • 🆕 Youngest ocean rocks are found near mid-ocean ridges.
  • ❗ Seafloor spreading contributes to continental drift.
  • 🔄 Equal-sized magnetic stripes prove seafloor spreading.
  • 🌊 Seafloor spreading helps oceans expand or shrink.
  • 🧪 Evidence from fossils, rocks, and geomagnetic data support these theories.

Timeline

  • 00:00:00 - 00:07:53

    The lesson aims to explain seafloor spreading and magnetic reversal as evidence of plate tectonics. Previously, the Continental Drift Theory by Wegener suggested a supercontinent Pangea existed 200 million years ago and broke apart. The theory was initially rejected due to lack of a mechanism for drift. Enhanced exploration in the 1950s-60s led to the discovery of mid-ocean ridges, providing grounds for the Seafloor Spreading Theory proposed by Hess, where magma creates new oceanic crust at these ridges. This process helps explain different rates of ocean size changes and provides core support for tectonic shifts.

Mind Map

Video Q&A

  • Who proposed the seafloor spreading theory?

    The seafloor spreading theory was proposed by Harry Hess and Robert Dietz.

  • What does the seafloor spreading theory explain?

    The seafloor spreading theory explains that new seafloor is created at mid-ocean ridges where hot material rises, cools, and forms new oceanic crust.

  • Why was the continental drift theory not initially accepted?

    The theory of continental drift was not initially accepted because it did not explain how continents moved.

  • What is seafloor spreading?

    Seafloor spreading is the process where new ocean floor is created at mid-ocean ridges and shifts continents apart.

  • What is magnetic reversal?

    Magnetic reversal refers to the switching of Earth's magnetic poles, which is recorded in oceanic rocks and supports seafloor spreading.

  • How do rock and sediment patterns support seafloor spreading?

    Rocks at the mid-ocean ridge are younger, and sediments are thinner compared to those at continents.

  • Why is the Atlantic Ocean getting wider?

    The Atlantic Ocean is getting wider due to faster seafloor spreading compared to subduction rates.

  • How do magnetic stripes indicate seafloor spreading?

    Magnetic reversals are recorded as stripes in rocks on the ocean floor, showing equal size and polarity which indicate spreading from the ridge.

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  • 00:00:20
    [Music]
  • 00:00:23
    today's discussion will focus on the
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    learning competency
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    enumerate the lines of evidence that
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    support plate movement
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    at the end of the lesson you should be
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    able to one
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    explain the seafloor spreading theory
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    and number two describe magnetic
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    reversion
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    as evidence of the sea floor spreading
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    previously you learned about continental
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    drift theory which suggests that around
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    200 million years ago
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    a super continent called pangea broke
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    down into smaller super continents named
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    loratia and gondwanaland
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    these supercontinents broke into
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    continents that we have
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    in the present time this theory was
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    supported by the following evidences
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    first the continental jigsaw puzzle
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    evidence from fossils
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    evidence from rocks
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    the glacial striation
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    and the cold deposits
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    despite the evidence as presented by
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    wagener his idea that the continents
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    were once joined together was not
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    accepted by the scientific society
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    because he wasn't able to explain how
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    this drifting took place
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    this made scientists conduct further
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    studies in search
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    for the answer during the 1950s and
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    1960s
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    new techniques and modern gadgets
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    enabled scientists
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    to make better observations and gather
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    new information about the ocean floor
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    they have discovered underwater features
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    deep within the ocean
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    scientists found a system of ridges or
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    mountains in the seafloor similar to
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    those
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    found in the continents these are called
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    mid ocean ridges
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    one of this is the famous mid-atlantic
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    ridge
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    an undersea mountain chain in the
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    atlantic ocean
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    in the early 1960s scientist harry hess
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    together with robert jetz suggested an
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    explanation to the continental drift
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    this is the sea floor spreading theory
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    [Music]
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    according to this theory hot less dense
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    material from below the earth's crust
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    rises towards the surface of the mid
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    ocean ridge
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    this material flows sideways carrying
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    the seafloor away from the ridge
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    and creates a crack in the crust the
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    magma flows out of the crack
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    cools down and becomes the new sea floor
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    over time the new oceanic crust pushed
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    the old oceanic crust
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    far from the ridge
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    the process of seafloor spreading allow
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    the creation of new bodies of water
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    for example the red sea was created as
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    the african plate and the arabian plate
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    moved away from each other
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    seafloor spreading is also pulling the
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    continents of
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    australia south america and antarctica
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    away from each other in the east pacific
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    rise
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    the east pacific rise is one of the most
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    active sites of sea floor spreading
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    with more than 14 centimeters every year
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    in the place where two oceanic plates
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    collide or where an oceanic plate and a
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    continental plate collide
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    a subduction zone occurs
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    the rate of formation of a new sea floor
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    is not always as fast as the destruction
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    of the old seafloor at the subduction
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    zone
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    this explains why the pacific ocean is
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    getting smaller
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    and why the atlantic ocean is getting
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    wider
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    what is the reason behind this if the
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    subduction
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    is faster than seafloor spreading the
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    ocean shrinks
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    when the sea floor spreading is greater
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    than the subduction
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    then the ocean gets wider and here are
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    the findings that support
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    seafloor spreading theory one rocks are
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    younger at the mid-ocean ridge
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    second rocks far from the mid-ocean
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    ridge
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    are older
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    third sediments are thinner at the ridge
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    and number four rocks at the ocean floor
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    are younger than those at the continents
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    the sea floor spreading theory was
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    strengthened with the discovery of the
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    magnetic reversal patterns
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    in rocks a magnetic compass tells us the
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    directions
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    on earth it also proves that the earth
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    has a magnetic field
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    the needle of a magnetic compass usually
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    points to the north pole of the earth
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    which is actually the south magnetic
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    pole at present now
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    what is magnetic reversal how does
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    magnetic reversal happen
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    and how does it prove sea floor
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    spreading
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    the earth's magnetic field is generated
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    in the very hot molten outer core
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    and has already existed since the birth
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    of our planet
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    the earth's magnetic field is a dipole
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    one that has a north pole
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    and a south pole
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    magnetic reversal is also called
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    magnetic flip
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    of the earth it happens when the north
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    pole is transformed into a south pole
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    and the south pole becomes the north
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    pole
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    this is due to the change in the
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    direction of flow in the outer core
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    the occurrence of magnetic reversals can
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    be explained through the magnetic
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    patterns in magnetic rocks
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    especially those found in the ocean
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    floor when lava solidifies
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    iron-bearing minerals crystallized as
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    this crystallized
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    the minerals behave like tiny compasses
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    and align with the earth's magnetic
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    field
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    so when the magnetic reversal occurs
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    there is also a change in the polarity
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    of the rocks
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    this allowed scientists to visualize the
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    magnetic stripes in the ocean floor
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    and to construct a magnetic polarity
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    time scale
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    over the last 10 million years there has
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    been an average
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    of four to five reversals per million
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    years
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    new rocks are added to the ocean floor
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    at the ridge which approximately equal
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    amounts
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    on both sides of the oceanic ridge
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    the stripes on both sides are of equal
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    size and polarity
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    which seem to be mirror images across
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    the ocean ridge
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    what does this indicate it indicates
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    that
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    indeed the sea floor is spreading
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    and that ends our lesson i hope you
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    learned something today
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    thank you for watching
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    [Music]
  • 00:07:52
    you
Tags
  • plate tectonics
  • seafloor spreading
  • magnetic reversal
  • continental drift
  • mid-ocean ridge
  • Pangaea
  • subduction
  • magnetic stripes
  • oceanic crust
  • tectonic plates