Download Plate Tectonics

Plate Tectonics
The Earth’s Crust in Motion…
Earth’s Interior
•
•
Scientists have not been able to
directly study much of the earth’s
interior due to high temperatures and
pressures. They do get much of the
information they possess from the
study of seismic waves (shock waves
produced by earthquakes). These are
measured by an instrument known as
a seismograph.
There are 3 types of seismic waves
– Primary waves (P waves). These
are the fastest seismic wave.
They travel through any material
but are slowed by less dense
materials such as liquids & gases.
They are push/pull waves.
– Secondary waves (S waves).
These are slower waves that will
not travel through liquids. They
are upward waves that cause the
land they travel through to move
at right angles.
– Surface waves (L waves). These
bend and twist Earth’s surface &
cause the most damage at the
surface.
Structure of the Earth’s Interior
The Core
• The center of the earth.
• The core is split into 2 layers
the solid inner core and the
liquid outer core. Both layers
are made of iron and nickel.
• The composition of the core
and rotation of the Earth
causes a magnetic field called
the magnetosphere.
• The inner core is very dense
due to pressure & has a
temperature of around 50000C.
• The diameter of the inner core
is approximately 2600 km
(1616 miles). It is found 5150
km (2781 miles) below the
surface.
• The outer core (liquid) is 2900
km (1802 miles) below the
surface and 2250 km (1398
miles) thick.
The Mantle
• The middle layer of the Earth.
• The largest layer of the Earth.
(80% of volume 68% of mass).
• The mantle is made mostly of
silicon, oxygen, magnesium
and iron.
• There is more iron as you get
closer to the core.
• The temperatures range from
870C near the crust to 2200C
near the core.
• The mantle is a solid but it can
flow like a liquid so it has a
property known as
plasticity(This is similar to
mercury or Jell-O or silly putty).
• Sample of the mantle have
been taken beneath the ocean.
The Crust
• The thin outermost layer of the
•
•
Earth.
The crust is made mostly of
silicon, oxygen and 6 trace
elements.
There are 2 types of crust.
– Continental crust – crust
beneath the continents.
Average thickness is 32
km (19.84 miles). It is
thicker beneath mountains.
Mostly made of igneous
rocks granite and basalt.
– Oceanic crust –crust
beneath the ocean.
Averages 8 km (5 miles)
thick. Mostly made of
basalt.
•
Lithosphere- The topmost solid
part of the earth where life exists.
The lithosphere is made of 7
major plates that are split into
minor plates.
The Moho
• Short for Mohorovičić
discontinuity.
• A thin layer of AIR
between the crust and
mantle.
• It explained jumps on
the seismograph.
• Identified in 1909 by
Andrija Mohorovičić, a
Croatian seismologist
The letter A is the Moho
Continental Drift
•
•
•
The theory made by German
meteorologist Alfred Wegner in
1912. It said that the continents
used to all be together in a
supercontinent called Pangea
which drifted apart and are still
moving.
3 pieces of evidence to support
this theory
– 1.continent boundaries fit
together like a
puzzle
– 2.fossils of same organisms
found on different continents
• a. Mesosuras- reptile
• b. Glosopteris- fern plant
– 3.Glaciar evidence in different
climates
*Wegner was not believed for a
long time because he could not
give a way for the continents to
move. The discovery of
lithospheric plates and sea floor
spreading helped to give his
theory more credibility.
Supercontinent
Pangea – means all lands
Tens of Millions of years!
Plate Tectonics and Sea Floor
Spreading
• Plate tectonics – theory that
earth’s crust is made of plates
that move driven by convection
currents in the asthenosphere
and sea floor spreading.
• (Based on continental drift
ideas but stronger).
• Sea floor spreading – a
hypothesis that there is a crack
between plates under the sea
that allows magma to reach
the surface and form new
seafloor
How does it work?
Plates – pieces of the
lithosphere
Plates fit closely together
along cracks called Plate
Boundaries
Convection Currents in
asthenosphere cause
movement
Earth’s Puzzle
• What plate do we live on?
• What plates do we border?
• USGS Earth’s Plates
• How far do we move every year?
Types of Boundaries
• Divergent
• Convergent
• Transform
A
Divergent
•plates are
moving apart
•new crust is
created
•Magma is
coming to the
surface
B
Convergent
•plates are coming
together
•crust is returning
to the mantle
•Subduction
(pushing down) is
occurring
C
Transform
•plates are
slipping past
each other
•crust is not
created or
destroyed
A
Divergent
Continental crust
 rift valley
B
Convergent
2 continental plates 
mountain range
C
Transform
Plates move
against each
other
Stress builds up
Oceanic crust  midocean ridge
2 oceanic plates or
oceanic +
continental
subduction or
underwater
mountains
Stress is released
earthquake
The Big Picture
The Big Picture 2