Plate Tectonics
What’s Inside Earth? (26min)
Earth’s Layers
• Earth is described by the many different layers
that make it up:
– Outer Layers:
• Atmosphere
• Hydrosphere
• Biosphere
– Inner Layers:
• Lithosphere
• Mantle
• Core
Inner Layers
• The inner layers of Earth
are separated into three
different regions:
– Lithosphere – Consists of
the crust and upper mantle
– Mantle - Consists of the
asthenosphere and
mesosphere
– Core - Consists of the outer
core and inner core
The Lithosphere
• The lithosphere is the
layer of solid rock that
forms Earth’s outer
surface; dry land &
oceans
– Very thin: 5-50km thick
• 2 Layers:
1. Oceanic Crust
• Crust beneath the ocean
2. Continental Crust
•
Crust that forms the
continents.
Oceanic Crust
Lithosphere
Continental
Crust
The Mantle
• Earth’s largest layer
• 2 Layers:
1. Asthenosphere
•
•
Soft and bendable
Asthenes = Greek for “weak”
2. Mesosphere
•
Solid rock below the
asthenosphere.
The Core
• 2 parts:
1. Outer Core
•
Liquid – molten metal
(iron & nickel)
2. Inner Core
•
Solid metal (iron & nickel)
• Both Inner and Outer
cores make up 1/3 of
Earth’s mass but only
15% of its volume.
Earth’s Continents
• Earth has 7 continents, great landmasses
surrounded by water.
– Have these landmasses always been in their current
location or have they moved throughout history?
Drifting Continents
• 1910, German scientist Alfred Wegener was
curious about the relationship of the continents.
– Formed a hypothesis that Earth’s continents have
moved.
– He began to study:
• The landforms on Earth
• The fossils on different continents
Landforms
• In looking as Earth’s
landmasses he noticed
that the continents looked
like puzzle pieces that
could fit together.
• He believed that the
continents had once been
joined together in a single
landmass and had since
drifted apart – Pangaea,
“all lands”.
Permian – 225mya
Jurassic – 150mya
Triassic – 200mya
Cretaceous – 65mya
Present Day
Fossils
• When looking at the locations of fossil remains,
Wegener noted that they occurred at locations that
would have been connected during Pangaea.
Confirming Wegener’s Theory
• New technology in the
1950-60’s confirmed
Wegener’s theory of
Continental Drift – the
hypothesis that the
continents have slowly
moved across Earth’s
surface.
– Sonar bounces sound waves
off underwater objects.
• The time it takes for the echo
to arrive back indicates the
distance to the object.
Our Ocean Floor
• With the use of sonar we have been able to map
the ocean floor.
– Oceans cover ¾ of Earth’s surface and we can’t see
the bottom of the oceans. Without sonar we would
not know how the bottom of the oceans look.
• Characteristics of the Ocean Floor:
– Mid-Ocean Ridge
– Rift Valley
– Deep-Ocean Trenches
Mid-Ocean Ridge
• The mid-ocean ridge is an under water
mountain range that extends into all of Earth’s
oceans.
– Over 50,000km long
Mid-Ocean Ridge
• A valley runs the length of the mid-ocean
ridge, right down its center = Rift Valley.
– Twice as deep as the Grand Canyon.
Sea-Floor Spreading
• The ocean floor moves like a conveyor belt,
carrying the continents.
– Molten material rises from the mid-ocean ridge,
pushing older rock to both sides and creating new
ocean floor.
Subduction
• The ocean floor does not just keep getting
wider and wider. Instead it plunges into deep
underwater canyons called deep-ocean
trenches – Subduction Zones.
– The oceanic crust is more dense than the
continental crust. When the two meet the oceanic
crust sinks back into the mantle.
Subduction
Lithospheric Plates
• Earth’s lithosphere is not a solid outer crust but
cracked or broken into several pieces - Plates.
• The Theory of Plate Tectonics states that pieces
of Earth’s lithosphere are in constant, slow
motion, driven by convection currents in the
mantle.
– No plate can budge without affecting the other plates
surrounding it; plates collide, pull apart or grind past
each other.
• Links the ideas of continental drift and ocean
floor spreading.
Earth’s Lithospheric Plates
Plate Boundaries
• Plate boundaries are where two plates meet.
• Depending on the direction the plates are
moving you can have three different types of
plate boundaries:
1. Transform – sliding past
2. Divergent – moving apart
3. Convergent – moving together
Identifying Plate Boundaries
• Put the letter of the correct answer in the
space provided:
A.
C 1. Transform
_____
B.
_____
A 2. Divergent
_____
B 3. Convergent
C.
Transform Boundary
• Plates sliding past one
another, in opposite
directions
– Earthquakes often occur
here.
• Ex. San Andreas in,
California
Divergent Boundary
• Plates moving apart
• Oceanic spreading
centers
– Mid-Atlantic ridge
• Rift Valleys – on land
– Great Rift Valley in East
Africa.
Convergent Boundary
Moving together
– The density of the plates determines which one
comes out on top:
1. Oceanic vs. Continental
Subduction
Convergent Boundary
2. Oceanic vs. Oceanic
– Both oceanic crusts sink forming volcanic island
arc
Convergent Boundary
3. Continental vs. Continental
– Land masses fuse together
– Uplift and folding of land
– Major mountain ranges
• Himalayas