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Plate Tectonics
Earth’s Layers
The Earth's rocky
outer crust solidified
billions of years ago,
soon after the Earth
formed.
This crust is not a solid
shell; it is broken up into
huge, thick plates that
drift atop the soft,
underlying mantle.
The Crust
• Outermost layer
• 5 – 100 km thick
• Made of Oxygen, Silicon, Aluminum
The Mantle
• Layer of Earth
between the crust
and the core
• Contains most of
the Earth’s mass
• Has more magnesium and
less aluminum and silicon than
the crust
• Is denser than the crust
The Core
• Below the mantle
and to the center of
the Earth
• Believed to be
mostly Iron,
smaller amounts of
Nickel, almost no
Oxygen, Silicon,
Aluminum, or
Magnesium
Tectonic Plates
Plate Tectonics
• Greek – “tektonikos” of a builder
• Pieces of the lithosphere that move around
• Each plate has a name
• Fit together like jigsaw puzzles
• Float on top of mantle similar
to ice cubes in a bowl of water
The Keys Features of Plate Tectonics
(1) The Earth’s crust is constantly being created and
destroyed (recycled).
(2) Ocean crust, formed at divergent margins, is mafic
and dense.
(3) As ocean crust ages and cools, its great density relative
to the continents results in subduction as plates converge.
[As a result, old ocean crust cannot persist, whereas old
parts of the buoyant continents can survive for eons.]
(4) The other kind of plate margins, transforms, are
parallel to the current motion of the plates.
How Plates Move
http://pubs.usgs.gov/gip/dynamic/unanswered.html
Mechanisms of Plate Tectonics:
1
RidgePush
2
3 Mantle
drag
convective flow of mantle
Mechanisms of Plate Tectonics:
4
PlumeDriven
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
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
Stress is released
earthquake
Different Types of Boundaries
http://pubs.usgs.gov/gip/dynamic/understanding.html
Divergent Boundary –
Arabian and African Plates
Divergent Boundary –
Iceland
http://pubs.usgs.gov/gip/dynamic/understanding.html
Divergent Boundary - Oceanic
http://www.geology.com
Divergent Boundary - Continental
http://www.geology.com
Convergent Boundary – Indian and Eurasian Plates
Convergent Boundary – Oceanic
& Continental
http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com
Convergent Boundary – Oceanic & Oceanic
http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com
Convergent Boundaries - Continental
http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com
Transform Boundary – San
Andreas Fault
www.geology.com
Ridge Segment
Divergent and
transform boundaries
can occur together at
mid-ocean ridges
Scripps Classroom Connection