Transcript Plate Tectonics-1-1

Section 1: Earth’s Interior
Who Studies Earth’s Interior?
Geologists
Scientists who study the forces that make and
shape planet Earth.
 They study the processes that create Earth’s
features and search for clues about Earth’s
history.
What kind of evidence do scientists use
to learn about the interior of the earth?
Direct
vs. Indirect
Direct evidence: from rock samples.
Scientists
drill up to 12 km into the earth. Forces blast
rock from as deep as 100 km.
Indirect evidence: from seismic waves
How do scientists study the Earth?

To reach the Earth’s core you would have to travel over 6,000
km (3,728 miles)!

Scientists record Seismic Waves – a vibration that travels
through Earth carrying the energy released during an
earthquake

Types of seismic waves –
P waves – travel through crust (6km/sec) and mantle
(8km/sec)
S waves – will not travel through liquid
http://aspire.cosmic-ray.org/labs/seismic/seismic.swf
What is the Earth’s structure?

The Crust

The Mantle

Lithosphere

Asthenosphere
The Core



Outer Core
Inner Core
What is the structure of the crust?
rock that forms the
Earth’s outer skin including the
rock under the ocean

A layer of

Two types of crust:
Continental Crust
Granite – less
dense
crust
Oceanic Crust
Basalt – more dense rock
What is the structure of the mantle?

Two major parts:
Lithosphere – upper part of
crust and mantle together;
floats on top of the asthenosphere
Asthenosphere –
softer than the mantle due to
increasing temperature and

pressure
The mantle is nearly 3,000 kilometers thick!
(1,864 miles)

What is the structure of the core?
Two parts

liquid
Outer Core –
; behaves like
a thick liquid; forces the solid inner core
spin causing Earth’s
magnetic field
Inner Core – solid; extreme
pressure squeezes the atoms
of iron and nickel so that they
to

cannot spread out to become liquid

Inner core and outer core are just
slightly smaller than the
moon
Chemical Layers
Physical Layers
Section 2: Convection and the Mantle
How does Heat transfer?
 Radiation – heat transfer
empty space; ex.
sunlight
through
 Conduction – heat
transfer through
contact
direct
 Convection- heat
transfer by
of heated
movement
fluids
How do convection currents affect
the Earth?

Heating and cooling a
fluid changes its
density; warmer fluids
have a lower density and
float; colder fluids have
a higher density and
sink
Section 3: Drifting Continents
Were the continents once together?

Wegner hypothesized that all
the continents had moved from a
supercontinent known as Pangaea.
Alfred
What is the evidence for Wegner’s idea?

Evidence of Continental Drift:
Landforms – similar mountain ranges
Fossils – similar fossils of a fernlike plant existed
on both continents
Climate – tropical plant fossils found in cold
climates
Section 4: Sea-Floor Spreading
What is happening in the ocean?
 Using sonar scientists
discovered mountains
under the ocean

The longest chain of
mountains in the world is
under the ocean and is
known as the MidOcean ridge!
Side-scan sonar locates
missing plane
Courtesy of NOAA.
Side-scan sonar image of the
remains of the submarine USS O-9
(SS-70) off the Isle of Shoals, New
Hampshire in more than 400 feet of
water.
Courtesy of NOAA.
What is sea-floor spreading?

Harry Hess suggested that
at the mid-ocean ridge
molten material rises
from the mantle and
erupts; pushing older
rock to both sides
 This process is known as
sea-floor spreading!
What is the evidence for Sea-floor
spreading?
 Evidence from
Molten Material
 Evidence from
Magnetic Strips
 Evidence from
Drilling Samples
How can the ocean floor keep from
getting wider and wider?

The older ocean floor
plunges into deep-ocean
trenches in a process
known as subduction
 Sea-floor spreading
and subduction work
together like a giant
conveyer belt!
Section 5: What is the theory of plate
tectonics?

The Earth’s lithosphere is
cracked into separate
sections known as plates
 Geological theory states that
these plates are in
constant, slow motion,
driven by the convection
currents in the
mantle
How is the theory of plate tectonics
different from continental drift?
drift is based on the movement of
the continents DUE to plate tectonics
 Continents are NOT the same as plates
 Tectonic plates can be made up of both
oceanic crust and continental crust
 Continental
What happens where the plates meet?

Plate Boundaries –
edges of the
lithosphere meet; faults
where the
form along these boundaries:
Transform
Divergent
Convergent
What are Transform boundaries?

The place where two
plates slip past each
other, moving in
opposite directions
Earthquakes occur
frequently at these
boundaries
What are Divergent Boundaries?

The place where two
plates move apart,
or diverge and create a
rift valley

Most occur at the mid-
ocean ridge although
some can occur on land
What are Convergent
boundaries?
 The place where two plates come
together, or converge creating a
collision
Subduction occurs at
convergent boundaries

density
crust
The
of the
determines which curst will be on
top – if both plates are the same
density they form a
mountain range