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Earth Systems
Earth’s Layers and Plate Tectonics
How many layers is the Earth dived
into?
• The earth has four main layers and those
layers are divided even further into sub-layers.
• Scientists have learned about the structure of
the Earth through deep drilling and seismic
evidence.
How many layers is the Earth dived
into?
The earth has four distinct layers:
–Crust (continental and oceanic)
–Mantle (upper: asthenosphere and
lower)
–Outer Core
–Inner Core
Layers of Earth
What is the Crust?
• The crust or “thin shell” that covers the globe is the
first layer.
• 60-70% covered water
• 30-40% seven continental continents
What is the difference between Continental
Crust and Oceanic Crust?
• The continental crust is the rigid and brittle
layer of igneous, sedimentary, and
metamorphic rocks which form the
continents. The age of these rocks varies from
between 4 billion to 600 million years. Even
though it has all types of rocks the majority is
granitic rock, so continental crust has a
density of about 2.7 g/cm3 .
• It ranges in thickness of 20-70 km. The
thickest crust is found in mountain ranges.
What is the difference between Continental
Crust and Oceanic Crust?
• Oceanic crust is the layer of mostly basalt
found under the oceans.
• The average density of the oceanic crust is 3.3
g/cm³. It ranges in thickness of 5 -10 km.
• Oceanic crust is created at the mid-oceanic
ridges and destroyed at the oceanic trenches.
Oceanic crust is relatively young age and is
being created even today at mid-oceanic rift
zones. Maximum age is about 200 million
years.
Mid Ocean Ridge
Oceanic Trench
Is the crust one big piece or multiple
pieces?
• The Theory of Plate Tectonics (1960) states
that the Earth’s crust is made up of about a
seven major plates on which the continents
and oceans rest and that these plates are in
constant slow motion.
What are the seven major plates?
• North American Plate, Eurasian Plate, Pacific
Plate, Nazcan Plate, South American Plate,
Indo-Australian Plate, and African Plate.
Are there any combined regions?
• The crust and the upper part of the mantle is
called the lithosphere. This is a solid, rigid
area.
Crust and Lithosphere
Where is the mantle and what are its features?
• The mantle is located below the crust and it
contains mostly Fe, Mg, Si, Al, and O.
• The mantle has an upper portion and a lower
portion.
• The asthenosphere is the molten, ductile,
upper portion of the earth's mantle and it
reaches a depth of about 250 km.
• The asthenosphere is a solid but it flows like a
liquid –this is known as plasticity.
Where is the mantle and what are
its features?
• The rest of the mantle extends to 2900 km.
The mantle has convection currents which
result from differential temperatures (2800 ◦C
to 3200 ◦C) in mantle materials.
• Convection currents are the vertical (rising
and falling) movement of rock within the
mantle. Convection currents are the driving
force that causes tectonic plates to move
around the Earth's surface.
Convection Currents
Where is the core and what are its
features?
• The core is broken up into two sections (inner
and outer core).
Outer Core Features
• The outer core is less dense than the inner
core and it is about 2,200 km thick.
• The temperatures reach between 4000 ◦C –
5000 ◦C.
• Due to the great temperature, the outer core
made of LIQUID iron (Fe) and nickel (Ni).
Inner Core Features
• The inner core is about 1,250 km thick.
• The inner core is denser and has temperatures
reaching 6000 ◦C.
• Even though it is hotter than any other part of
the layers of the earth, it is NOT liquid. The
inner core is SOLID because of the intense
pressure applied on it from all the layers
above.
• The material in the core is mostly iron (Fe).
Magnetic Field
• The currents of the outer core, cause the inner
core to spin. It spins at a faster rate than the
rest of the planet. This leads to the creation
of the Earth’s magnetic field.
Layers of Earth
How did Alfred Wegner come up with
his idea?
• In 1911 Alfred Wegner (German
geophysicist/meteorologist) began his quest
to prove that the continents were once
connected due to what he called “continental
drift.” It all started when Wegner was
browsing in the university library when he
came across a scientific paper that listed
fossils of identical plants and animals found on
opposite sides of the Atlantic.
Alfred Wegner Continued…
Intrigued by this information, Wegner began to
look for, and find, more similar cases of similar
organisms separated by great oceans. Alfred
Wegner also noticed that the different large
landmasses of the Earth almost fit together
like a jigsaw. America fit closely to Africa and
Europe and Antartica, Australia, India, and
Madagascar fit next to the tip of Southern
Africa.
What did Alfred Wegner propose?
• In 1912, he proposed the theory of
continental drift which hypothesized that the
continents were slowly drifting around the
Earth. He claimed that millions of years
before present Earth, the continents were all
connected. He called this huge landmass
Pangaea.
Pangaea (100 mya)
Present
Comparison
What evidence helps to support his
theory of Pangaea?
• Geologist have discovered that the geological
structures of rocks in South West Africa and
South East Brazil were distinctively identical,
and the age of the two rocks were the same.
• Fossils of the same species were found on
several different continents. Wegner
proposed that species dispersed were
together and later carried to their present
position as continents drifted.
What evidence helps to support his
theory of Pangaea?
• Coal can be found underneath the cold and dry
Antarctic ice cap, though coal can only form in warm
and wet conditions.
• Glossopteris, a fern, was found on the continents of
South America, Africa, India, and Australia.
• Mesosaurus, an early freshwater reptile, fossils are
both found in Africa and South America. Since this
animal inhabited freshwater habitats, it could not
have swam in the ocean with is salt-water.
Mesosaurus and Glossopteris
Is there proof that the plates move?
• Even though the crust is solid rock, it sits on
top of a hot, soft, semi-solid material located
in the mantle. As the material in the upper
mantle moves, it drags the overlying plates
across the Earth’s surface. The plates are
moving about 1 centimeter to 15 centimeters
per year in different directions. GPS (Global
Positioning Units) and satellites are used track
this movement.
What is the name of the area between the
crust tectonic plates?
• The border between two tectonic plates is
called a boundary.
What types of boundaries are
there?
• Convergent boundaries are areas under
pressure that either result in subduction
which is the lithosphere plates are driven
down and destroyed in the molten magma or
in crustal uplifting that leads to mountain
building.
Convergent Boundary-Subduction
Convergent Boundary-Mountain
Divergent Boundary
• Divergent boundaries are areas under tension
where plates are pushed upward by magma
uprising from the mantle.
Divergent Boundary
Transform Boundary
• Transform boundaries are areas that are
moving laterally past one another and creating
a shearing force.
Transform Boundary
When the plates move and interact, can
this cause natural events on Earth?
• When plates interaction through collisions,
plates sliding past each other, plates splitting
from each other, it can lead to the formation
of mountains, volcano eruptions, sea-floor
spreading and earthquakes.
When do mountain chains form?
• Mountain chains form when continental landmasses
that have the same rock density converge. Since
they have similar density, one plate can’t be
subducted under the other. The pressure of the
impinging plates can only be relieved by thrusting
skyward forming mountain peaks. For example, the
Himalayas, which stretch 2900km along the border
between India and Tibet formed between 40-50 mya
when India and Eurasia, driven by plate movement
collided.
Himalayan Mountains
When do earthquakes occur?
• Movement occurs along faults. Faults are large
cracks in the Earth’s crust. Rocks on either side of a
fault are under pressure and get locked together.
When too much pressure builds up, the rocks
suddenly slide past each other and release the
pressure. The result is an earthquake (violent
shaking on the Earth’s crust). The San Andreas Fault
is a transform boundary that connects the Pacific
plate with the N.A. plate.
San Andreas Fault
How do volcanoes form?
• Volcanoes form when material from inside the
Earth reaches the surface. In convergent
boundaries one plate can submerge under
another and the heat and pressure turn rock
into magma, which can rise through the cracks
in the crust. In divergent boundaries, where
plates pull apart, magma rises through cracks
and forms volcanoes.
Parts of a volcano
Types of Volcanoes
Is this the only way that volcanoes
form?
• The Hawaiian Islands, which are entirely of
volcanic origin, have formed in the middle of
the Pacific Ocean more than 3,200 km from
the nearest plate boundary. These volcanoes
form due to a hot spot (a constant up flow of
magma in a stationary location).
Hot Spot
Hawaii Island Formation