Continental Drift &Plate
Tectonics
Whitney Isbell for use with my 8th Grade Science Class
http://www.middleschoolscience.com 2013
Earth’s Layers
The Earth's solid
rocky outer crust
formed 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
• Lithosphere is made up of the crust
and the upper mantle. The
lithosphere makes up the plates that
move on top of the Asthenosphere.
The Mantle
• Layer of Earth
between the crust
and the core
• Contains most of
the Earth’s mass
• A think liquid like
silly putty
• Molten rock
The Core
• Below the mantle
and to the center of
the Earth
• Outer Core is molten
metal
• Inner Core is solid
metal
Continental Drift
Alfred Wegener 1900’s continents were
once a single land mass that drifted apart.
Fossils of the same plants and animals are
found on different continents
Shape of the continents fit together like
puzzle pieces
Rocks are found in different continents
that are the same composition
Called this supercontinent Pangea, Greek
for “all Earth”
245 Million years ago
Could not explain why the plates moved
http://members.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml
Evidence of Pangea
Tectonic Plates
In the 1960’s scientists
discovered seafloor
spreading and
convection of the
mantle caused the
plates to move.
This was the beginning
of the theory of plate
tectonics
Convection: Heat rises and cool things sink due to density. Magma (molten
rock) that is close to the outer core is hotter and begins to rise. As the magma
(molten rock) gets closer to the crust it begins to lose heat and sink back
down towards the core. This creates convections currents which cause the
plates to move.
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
Sea Floor Spreading
Sea Floor Spreading
• Mid Ocean Ridges –
underwater mountain chains;
largest is the Mid-Atlantic
Ridge where the Atlantic ocean
is pulling apart and new land is
being formed.
• Magma rises to the surface
and solidifies and new crust
forms
• Older Crust is pushed
farther away from the ridge
How Plates Move
Convection
Currents
http://pubs.usgs.gov/gip/dynamic/unanswered.html
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
Mid Ocean Ridges
http://www.geology.com
You can see the
Mid-Atlantic
Ridge from
space
Magma rises to the surface when plates
are pulling apart and form new land
Divergent Boundary – Continental
Rift Valleys (Great African Rift Valley)
http://www.geology.com
New Land was
formed in Africa
when two plates
were pulling apart
Convergent Boundary – Indian and Eurasian Plates
Convergent Boundary – Oceanic & Continental
Oceanic Plates are denser
and will subduct (sink)
under continental plates.
The sinking oceanic plate
will form new magma.
http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com
Convergent Boundary – Oceanic & Oceanic
Because plates are not
the same size the larger
oceanic plate will
subduct under the less
dense oceanic plate and
form new magma.
http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com
Convergent Boundaries - Continental
Two continental
plates will buckle
against each
other and from
folded mountains.
http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com
Transform Boundary – San Andreas Fault
www.geology.com
Two plates that are sliding past
each other will create earthquakes
and faults.
• Fundamental Questions
• What was the early theory of continental drift; who
developed it, and when was it developed?
• What were the discoveries that led to a theory of plate
tectonics, and when were these discoveries made?
• What is Earth's lithosphere made of, and how does it affect
crustal features?
• What features of the Earth's crust do convergent, divergent,
and transform boundaries form?
• What land features formed by the movement of tectonic
plates can be observed using images from space?