Transcript Section 5: What is the theory of plate tectonics?

Section 1: Earth’s Interior
Who Studies Earth’s Interior?
Geologists
Scientists who study the forces that
shape planet Earth.
They study the processes that create Earth’s
features and search for clues about Earth’s
history.
make and

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
inner core to spin causing
Earth’s magnetic field
 Inner Core – solid; extreme
pressure squeezes the
atoms of iron and nickel so

Outer Core –
; behaves
like a thick liquid; forces the solid
that they 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 through
space; ex.
empty
sunlight
 Conduction – heat
transfer through
contact
direct
 Convection- heat
transfer by
movement of
heated
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
Alfred
hypothesized that all the
continents had
moved from a
supercontinent known as
Pangaea.
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 Mid- Ocean
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.
http://www.dailymail.co.uk/news/article-2112456/Titanicpictures-Extraordinary-sonar-images-map-shipwreck-oceanfloor.html
SONAr image of the Titanic (2.5 miles below sea level)
Debris field surrounding the stern of the ship
Bow and stern
sections rest 1.5
miles apart from
each other.
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
cracked
is
into
separate sections known as
plates

theory
Geological
states that these plates are
constant
in
, 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
where the
of
the lithosphere meet;
faults 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
creating a
collision
converge
Subduction occurs at
convergent boundaries

density
crust
The
of the
determines which curst will be
on
– if both plates are the
top
same density they form a
mountain range