History of geological science: Continental Drift is not plate tectonics. Jigsaw fit of continents was noted by Alfred Wegener, a german meteorologist he proposed

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History of geological science Continental
Drift is not plate tectonics.Jigsaw fit of
continents was noted by Alfred Wegener, a german
meteorologist he proposed Continental Drift
in 1915 saying the continents once fit together
as one and naming the supercontinent Pangaeathe
idea was considered absurd-gtno mechanism for
moving continents
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Wegeners evidence1. fit of continents2.
matching up past glaciations3. distribution of
equatorial climate belts4. distribution of
fossils/ fauna across continents5. matching up
of rocks/geologic unitsCriticism explanation
for how it could happen did not make
sense---continental crust cant plow through the
ocean crust
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Wegener-Continental Drift
This animation presents a view of the continents
at the level of map precision available to Alfred
Wegener, who proposed that the continents once
existed as a vast supercontinent, Pangea, that
later fragmented. Test the fit of the continents
for yourself by clicking and dragging a continent
to a new location then, using the arrow keys on
your keyboard, rotate the continent into
position. ?PC version ?Mac version
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2. Matching up of past glaciations
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3. Equatorial climate belts
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4. Matching up of fauna
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5. Matching up of rocks, geological units
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The story unfolds paleomagnetismAs we talked
about earlier, Earth has a magnetic field.It is
due to convection of the molten Fe in the outer
core (geodynamo)magnetic north pole is not the
geographic north pole- the difference for a given
location is the declination the Earths
magnetic field has a component of direction (N-S)
and a dip angle (magnetic inclination)both can
be recorded in magnetic minerals
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the direction of the field is easily recorded in
some minerals, especially magnetite just like a
compass needles, tiny grains of magnetite (or a
few other Fe bearing minerals) crystallize in
rocks at the surface. The little magnetic domains
in these minerals align with the magnetic field
(once they are below the curie Temperature)this
gives1) direction to magnetic N pole2) the dip
of the field which depends on latitude.
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More troublePaleomagnetic analysis along with
radiometric dating indicated the magnetic N pole
was moving all over the place with time-worse
yet, different continents gave different polar
paths -gt this was called apparent polar
wanderWait! If the same data were interpreted
to reflect a fixed pole but wandering continents,
everything worked. YIKES!But still, how do
continents drift???
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More info ocean depth
Hard to know the shape of the ocean floor-not
until WWII did sonar develop to measure
bathymetry (shape of seafloor surface). Right
in the middle of the Atlantic Ocean, there was a
big mountain range! There was also high heat
flow, a particular type of earthquake (reflecting
tensional forces) and sediment thickness
increased away from the mountain range
Seafloor bathymetry showed flat seafloor but big
mountain range in middle of the Atlantic...and
there was high heatflow in these mountains... and
these mountain ranges were locations of
particular type of earthquakes....
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One last piece of infomaps of earth quake
locations was not random--rather EQ found along
distinct belts including the mountain range in
the Atlantic
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Harry Hesss hypothesis

• Proposed the idea of sea-floor spreading
• Seafloor spreads and cracks
• Magma ascends and forms new oceanic crust made of
  volcanic rock
• Crust must be consumed somewhere--said it
  descends in ocean trenches.
• Testable as will be shown
• -gt got the big picture right but in detail more
  than just crust that is created and destroyed

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How to test the hypothesis
Paleo magnetics gets used again Geologists
working on volcanic rocks on land noticed that
the magnetic field of the Earth flipped
directions on an irregular basis (this has to do
with the geodynamo, and yes it could happen today
or tomorrow) These are called polarity
reversals Magnetometers towed across the
Mid-Atlantic Ridge revealed stripes of
alternating magnetic direction recorded in the
ocean crust--and it was symmetrical across the
ridge!
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Sea Floor Spreading
This animation shows progressive stages in the
opening of the Atlantic Ocean. The youngest rocks
(in red) clearly outline the mid-ocean ridge
system, complete with transform faults. The
oldest ocean crust (in blue), is confined to
offshore regions adjacent to the United States,
Canada and western Africa. This distribution
demonstrates that the North Atlantic began to
open before the South Atlantic. ?PC version ?Mac
version
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Magnetic Reversals
The polarity of Earth's magnetic field reverses
with time. The main figure demonstrates how
sea-floor anomalies, also known as magnetic
stripes, develop during sea-floor spreading. The
inset image records the reversal of Earth's
dipole. ?PC version ?Mac version
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Zoomable Art ?PC ?Mac
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Finally, radiometric dating of the volcanic rock
away from the ridge was the final proofThe
rocks got older away from the ridge confirming
that Hesss basic idea, that ocean crust was
created and destroyed allowing the continents to
move, was indeed correct.Next How Plate
Tectonics works