Download Notes: The Theory of Plate Tectonics

Notes: The Theory of Plate Tectonics
 Plate Tectonics is a _________ developed in the late 1960s, to explain how
the outer layers of the Earth ________ and __________.
 A theory was needed to explain why there are __________ prone areas,
why ____________ eruptions occur only in specific areas, and why there
are ocean __________ and ______________.
Some Previous Ideas
 Expanding Earth idea…In the beginning the Earth’s _________ was evenly
_________ over the ____________ ... but got stretched and thinned when
the _________ expanded forming the ocean __________.
 But, ocean _________ are too wide to have formed by any reasonable
__________.
 Contracting Earth idea…in the ____________ the Earth’s _________ was
evenly spread over the _________ ... as the mantle ___________, the
crust wrinkled forming ____________ and ocean ____________.
 But, wrinkles forming ____________ and ___________ should have
formed more evenly rather than in _____________ bands.
 Geosynclines idea … weight of __________ dumped off the edge of the
___________ sinks the _________ down into the __________ ...
eventually, it ___________ up to form _____________ ranges
 But, we see lots of ________ sinking down from the weight of
__________, but can’t find any that are ___________. Law of
___________ says that if you don’t see it happening now, you can’t
__________ it happened in the past.
Theory of Continental Drift
 Developed by _________ __________ in the early 1900’s, it said that the
___________ are like rafts ____________ over the ___________ crust.
 Wegener suggested that throughout Earth’s ________ the continents have
________ and __________ numerous times.
 Wegener called the most recent unified landmass __________. It began to
break apart about _______ million years ago.
 Wegener said that when ___________ ___________, ___________
ranges formed
 When ___________ separated or ___________, ocean __________
formed.
 Continental Drift Theory provided answers to some big mysteries. Like…
 The apparent ______________ fit of the ____________. This had been
noticed since the early days of map-making.
 And … The presence of identical ________ on widely __________
continents belonging to organisms that could not have __________ the
ocean or lived in the kind of __________ currently found in those locations.
 And …The presence of _________ tracks and deposits in areas that are,
today, far too _________ for glaciers. The ___________ of the tracks
were also problematic.
 But, Continental Drift Theory had its problems too. Like…
 Wegner was a ____________, who came up with his theory from watching
_____ flows. This didn’t ________ the geologists.
 But the biggest problem was that Wegner couldn’t provide an ___________
for how the continents were able to _________ that made sense.
 He said the continents ________ due to the earth’s _________ … and
________ through oceanic crust like an ice-breaker plowing through
________.
 People said that Wegner cited no __________, only __________. This led
some people to offer alternative ideas to ridicule ____________ Drift
 For example people noticed that a lot of the continents looked like _______
… suggesting that the __________ were dripping off ______________.
 Some geologist comments ...
 “Anyone who ________ his reputation for scientific sanity would _______
dare support such a __________.”
 "If we are to believe this __________, we must ________ everything we
have learned in the last 70 years and start all over __________,"
 __________ went back to his ice flows and _____ before seeing his ideas
gain ___________.
Plate Tectonics
 In the 1940’s _____________, Harry Hess, discovered a _______ down
the ________ of the Atlantic __________
 __________ analysis showed that the ________ of the ridge was very
______, like a long continuous ___________
 Analysis of ________ taken from the ocean bottom also showed a
symmetrical age pattern, ___________ in the middle, _________ at the
edges
 Geologists knew that the direction of _________ _________ changed
every million years or so.
 They also knew that when _________ cools, the __________ minerals
record the direction of ____________ North.
 When they checked the ocean crust around the ________ they found that
they recorded the _______ in long parallel stripes which corresponded to
the historical _________ of magnetic North
 Geologists now had strong ___________ that new ________ was being
__________ in the __________ of the Atlantic Ocean
 In fact, __________ is a volcanic island that sits right on _____ of the
Mid-Atlantic Ridge.
 If new crust was being ________ at the center of the mid-ocean ridge,
then somewhere else the old crust was being __________. Otherwise the
earth would be getting larger and larger.
 Confirming this was that the age of the ocean crust around the world
showed that none of it was older than ____ MY, less than a ___th of the
age of the _______ continental crust. Something was eating up the
crust!
 Oceanographers began to wonder about the long deep ________ they had
also discovered in the oceans, particularly the __________. Often these
trenches had _________ mountain chains along one side and had frequent
_____________.
 Geologists discovered that __________ crust was being warped
__________ into the __________ and being consumed at these
____________.
 As the ocean sediments and crust _________ the lighter elements would
well _________ forming the volcanic ___________ chains behind the
trench.
 These _________ formed a ring around the Pacific, characterized by
___________ and strong _____________ called the “________ ____
_______ ”
 With the discovery that ______ crust was being formed at Mid-Ocean
________ and _______ crust was being recycled at ________, Wegener’s
ideas got a new lease on life.
 With this new knowledge scientists were able to understand the _______
that was _________ enough to ________ continents and how the different
plate movements produced different __________!
 What makes the plates move? ___________
 What makes the plates stop? Convection ______ ______. Or something
______ the _______ together
 How fast do plates move? The ________ ________ has the ________
rate (less than ______ cm/yr), and the ______ ________ _______ near
Easter Island, in the South Pacific about 3,400 km west of Chile, has the
_________ rate (more than ____ cm/yr).
 Geologists eventually discovered that Earth’s ______ was cracked into many
_______, called _________, that are in constant _______ as a result of
sea-floor spreading.
 Different kinds of plate interactions are responsible for ________,
__________, and _____________.
 The solution to another _________ was suggested by the moving oceanic
crusts. The __________ has many long chains of ___________ that seem
to have been made one at a time in order. The ___________ chain is an
example of one of these.
 The ________ chain extends far ________ the surface island. The
Pacific island chains record the _________ of the Pacific plate over
_________.