Transcript Shortly after the Earth formed, heat released by colliding particles

The Earth’s Interior
Interior is characterized by gradually
increasing temps, pressure, and
density at increasing depths.
There are 3 main
layers in Earth’s
interior:
The top layer is called the
CRUST
– Oceanic: thin but dense (heavy, “sinks”);
composed of basalt rock
– Continental: thick but less dense; large variety
of rock, mainly granite.
Earth’s 2 main layer is called
the Mantle: 85% of the Earth’s
volume.
• The Mantle has a thin, solid part below the
crust.
• Next is a viscous layer similar to pudding or
silly putty (convection currents in this
viscous layer causes tectonic plates to slide)
• The bottom layer of the mantle is very
thick. It is solid.
Earth’s 3rd main layer is called
the Core
– Outer core: liquid iron that generates Earth’s
magnetic field
– Inner core: solid iron
Continental Drift: Alfred
Wegener’s theory
• Continents moved horizontally to their
current location.
• Believed that all continents were once one
large landmass called: PANGEA
Evidence of Continental Drift
• Fossils of mesosaurus and glossopteris
– Found widely in rocks on separate landmasses
• Rock types:
– Mountain ranges in South America and Africa are the
same.
• Climate evidence:
– Fossils of tropical plants found near Arctic Ocean
– Scratches in rocks made by glaciers found in South
Africa
Scientists did not support
Wegener’s theory because…
• He could not prove how, when, or why the
continental plates moved.
Sea Floor Spreading
• Harry Hess found evidence which helped
support the theory of continental drift.
• His theory was sea floor spreading.
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Evidence to support Sea Floor
Spreading
• Reverse Magnetic Polarity:
– The rocks were deposited with different
magnetic polarity based on the spin of the earth
• Age of rocks:
– The farther you are away from the spreading
center the older the age of the rock
Important things to remember from
the Theory of Plate tectonics:
• The lithosphere (crust & upper mantle) is
broken into puzzle pieces called tectonic
plates.
• Oceanic plates are more dense than
continental.
• Therefore, oceanic plates will be subducted
(pushed underneath) continental.
There are three types of
possibilities for plate collisions
When 2 plates collide…
• Oceanic to continental:
subduction
When 2 plates collide…
• Oceanic to oceanic:
volcanic ring or
islands
When 2 plates collide…
• Continent to continent:
mountain building
When plates move away from
each other under water…
• A mid-ocean ridge is
formed.
• Magma rises from within
the mantle at the midocean ridge. Magma is
called lava once it hits
Earth’s surface and flows
out to create new ocean
floor. This is a
constructive process since
there is a buildup of new
ocean floor.
When 2 plates slide past each
other…
• Two plates grind together and slip past each
other horizontally
No material made or destroyed
• Slipping causes…EARTHQUAKES!
• http://www.classzone.com/books/
earth_science/terc/content/
So how do the plates move?
• Remember the asthenosphere layer in the
mantle? It is the heated, soft-plastic-like
layer similar to silly-putty.
• The outward flow of heat from Earth’s
interior creates convection currents in this
soft layer, allowing it to flow slowly.
The motion is called convection cells
Global Positioning Systems (GPS)
• Scientists have been using GPS to verify
where plates used to be. They measure the
current speed of plate movements (in cm/yr)
with GPS, then backtrack. They also
observe offset geologic features such as
mountains, mid-ocean ridges, and
subduction zones.