Transcript Plate Tectonics

Plate Tectonics
Pacific Northwest
Mr. Rice
February 14, 2011
Introduction Video
In the beginning…
• Scientific evidence shows that out of a cloud and
fire storm from the sun, four billion six hundred
million years ago, earth was created…
• The sun burns the barren earth where there are
no seas and poisonous gases gasp the
inhospitable world…
• For thousands of years the earth is covered by
molten lava and is racked by volcanoes and
asteroids.
Eventually… layers form!
• Slowly, the earth cools and separates into multiple
different layers.
• Heavy metals, mostly iron, settles to the inner core
at the center of the earth.
• The inner core is slowly concealed in a nickel and
iron outer core that is less dense.
• Surrounding the inner and outer core is the mantle,
that is itself split in to many layers.
• Over the mantle is the Earth’s crust, a thin veneer of
rocky material that covers the planet like the
cracked, twisted, lumpy crust of an apple pie.
The Earth’s Layers
Plate Tectonics
• Once thought to be one solid piece of rock, the
earths crust is theorized to be made up of many
jostling plates.
• The plates are between 4-40 miles thick.
• These enormous blocks of Earth’s crust vary in
size and shape, and have definite borders that
cut through continents and oceans alike.
• There are nine major plates and many other
smaller plates.
Our World as Plates
How do Plates Move?
• Because the inner core is hot, because of
radioactive activity and the immense pressure,
rock melts as it dives downward.
• Then because of hot things rise and cold things
sink the liquid hot magma rises and hard rock
sinks, creating circulation.
• This circulation is called convection currents
• Convection currents are the reason that the light
plates move over the mantle.
Air Convection Currents
Convection Currents in the Earth
Types of Plate Boundaries
• Divergent Boundaries – Where earth is created
as two or more plates pull apart from each other.
• Convergent Boundaries – Crust is destroyed and
recycled back into the interior of the Earth as
one plate dives under another.
▫ Oceanic-Continental Convergent
▫ Continental-Continental Convergent
• Transform-Fault Boundaries – Where two plates
are sliding horizontally past each other.
Oceanic-Continental Convergence
• When an oceanic plate pushes
into and subducts under a
continental plate, the overriding
continental plate is lifted up and
a mountain range is created.
Even though the oceanic plate as
a whole sinks smoothly and
continuously into the subduction
trench, the deepest part of the
subducting plate breaks into
smaller pieces.
Continental-Continental Convergence
• When two continents meet head-on,
neither is subducted because the
continental rocks are relatively light
and, like two colliding icebergs, resist
downward motion. Instead, the crust
tends to buckle and be pushed upward
or sideways. The collision of India into
Asia 50 million years ago caused the
Eurasian Plate to crumple up and
override the Indian Plate. After the
collision, the slow continuous
convergence of the two plates over
millions of years pushed up the
Himalayas and the Tibetan Plateau to
their present heights. Most of this
growth occurred during the past 10
million years.
Different Types of Boundaries