Transcript NAVLANTMETOCCEN MASTER SLIDES

Plate Tectonics
What Goes On Beneath Our Feet
The Beginning Of Time


The time when the earth was born was called the Precambrian Era.
In this Era All of the continents were joined together in one huge
island called Pangea
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PLATE TECTONICS
Major Tectonic Plates of the World
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 In
addition to the continents drifting, large blocks of
heavier ocean floor are also being pushed about the
surface of the earth.
 The
study of this is known as “Plate Tectonics”. There
are about 20 oceanic and continent plates.
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Earth’s Plates
 The
pieces of the shell are Earth's tectonic plates (12 major
ones) and they float across a layer of soft rock like rafts in
a stream, their motions driven by forces generated deep in
the Earth.
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Continental Drift Reversed
Through the great
expanse of geologic
time, this slow
movement remakes the
surface of Earth,
expands and splits
continents, and forms
and destroys ocean
basins.
Drift Reversed
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How Old is The Earth
 The
age of Earth has been subject to debate.
Scientists now use an age of 4.6 billion years.
 Catastrophism
is the thought that Earth is very
young, and events described in the Bible are
responsible for the appearance of Earth’s features.
 The
principle of uniformitarianism was
introduced in 1788. This principle states that the
forces which shaped the Earth are identical to the
forces which are working today.
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Plate Movement
 At
their boundaries, the plates spread apart, converge,
and slide past one another.
 These
boundaries are the most geologically active regions
on Earth.
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Overview
 Here,
new land (crust) is born and old land is consumed.
 Hot
springs spew out mineral-rich waters, volcanoes
erupt, and earthquakes tremble -- resulting in devastating
tsunamis, floods, and mudslides.
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Alfred Wegener
1880 – 1930

In 1910, Wegener noticed the
matching coastlines of the
Atlantic continents -- they
looked on maps like they had
once been fit together.

He first spoke on the topic in
January of 1912, where he put
forth the idea of "continental
displacement" or what later
was called continental drift.
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Harry Hess
1906-1969
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Harry Hess proved Wegener's basic idea correct and clarifed the
mechanism that broke the once-joined continents into the seven
continents which we are now familiar with.
The continents are attached to the plates and do not move
independently of them. But the plates themselves shift and change
shape, carrying the continents along.
In 1960 he hypothesized that the seafloor was spreading from vents
in the Rift, where hot magma oozed up.
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John Tuzo Wilson
1908 - 1993
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During the 1960's he refined
and championed the theory of
plate tectonics, which was
then held in disrepute
Introduced the idea of "hot
spots" which remain
stationary under the moving
plates and produce chains of
islands like Hawaii and Japan
First to identify "transform
faults" which link trenches
(where the plates collide) and
rifts (where the plates pull
apart)
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Plate Movement
 When
the heat cells in the center of the
earth begin to move in a circular motion due
to convection the plates that sit on top of the
magma begin to move.
 Because magma is molten rock it doesn’t
move very fast so the moving of plates
takes a very long time
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PLATE TECTONICS
 Convection
currents in the mantle rise beneath the MidAtlantic Ridge and spread laterally along the base of the
plates.
 The
rocks flow back down into the mantle beneath
subduction zones.
 Magma
is present at very shallow depths immediately
beneath the Mid-Atlantic Ridge, not at deeper levels in the
convecting mantle.
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Divergent - Convergent

The plates move apart, away from the mid-ocean ridges
(Divergent).
The new crust eventually cools, and over time it is pushed to the
side by still more melted rock rising up from within the Earth, in
a continuous process (Convergent).
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
Plate Boundaries
The lithospheric plates interact with the neighboring plates in
several ways.
Divergent plate boundaries – Boundaries between plates moving
apart, further classified as:
Divergent oceanic crust – for example, the Mid-Atlantic Ridge
Divergent continental crust - for example, the Rift Valley of East
Africa.
Extension of
divergent
boundaries
causes splitting
and rifting.
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Plate Boundaries
♦Convergent Plate Boundaries - Regions where plates are pushing together
can be further classified as:
♦Oceanic crust toward continental crust - for example, the west coast of
South America
♦Oceanic crust toward oceanic crust - occurring in the northern Pacific
♦Continental crust toward continental crust – one example is the Himalayas
Compression
at convergent
boundaries
produces
buckling and
shortening.
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Compression
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M
o
u
nt
ai
ns
Mountains are formed when two plates collide into each other
and cause the land to crinkle and fold.
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Plate Boundaries
♦Transform plate boundaries - locations where crustal plates move past one
another, for example, the San Andreas fault.
Translation at transform boundaries causes shear.
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 Transform
plate boundary: plates slide past each other.
 The
San Andreas fault in California is an example of a
transform plate boundary, where the Pacific Plate slides
past the North American Plate.
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Tectonic Formations
 Some
formations that are formed by plate tectonics
are: mountains, ridges, valleys, trenches,
volcanoes.
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Ridges – Volcanic Mountains
 Ridges
are formed when the pulling apart of
a fault in the ocean floor causes magma or
“lava” to ooze through and form a bump on
the ocean floor.
 Over time these bumps turn into a formation
like the woops on a dirt bike track, accept
its on the bottom of the ocean floor.
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Ridge System
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Valleys

Valleys are formed
when two plates,
continential or
oceanic, collide
together if the land
isn’t pushed
upward it gets
pushed down and
forms a valley.
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Trenches – Undersea Valley
 Trenches
are formed when two plates push toward each
other and there is a valley in between the plates.
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 Eventually,
after more than 150 million years, the cold
crust is carried to subduction zones (places where one
plate sinks beneath another), where it sinks back into the
Earth -- dipping beneath another oceanic plate, or beneath
a continent -- and melts once more.
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PLATE TECTONICS
 The
North American and the Eurasian Plates are made
of rigid mantle and oceanic and continental crust.
 The
Mid-Atlantic Ridge is the boundary between the two
plates. New oceanic crust is created at the ridge.
 The
Mid-Atlantic Ridge is an example of a divergent
plate boundary. Because the plates are diverging, the
distance between North America and Europe is increasing.
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Volcanoes
 Volcanoes
are formed
when magma makes
its way to the surface,
accumulates a
mountain as it cools
and then is a giant
mountain of cold
magma.
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RING
OF
FIRE
 Subduction
zones, like the so-called Ring of Fire that
surrounds the basin of the Pacific Ocean, are among the
most violent on Earth.
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RING OF FIRE
 The
scraping of one plate on another generates powerful
earthquakes; the heating of the plate within the depths of the
mantle releases fluids which melt the rock over it,
producing molten rock (magma) that surface as volcanoes.
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EARTHQUAKES – Transform Faults
 Earthquakes,
too, can occur outside of the plate boundaries.
 Within
the interior of a plate, stresses -- from buckling,
stretching, or compression of the rock -- can build up, until
the rock finally breaks crating an Earthquake.
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The End
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Directed by: Phyllis Butler
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