Transcript KS4 Earth`s Structure 4763KB

KS4 Physics
Earth’s Structure
1 of 20
32
© Boardworks Ltd 2005
2004
Contents
Earth’s Structure
Earth and earthquakes
Seismic waves
More about plate boundaries
Continental drift
Summary activities
1
2 of 20
32
© Boardworks Ltd 2005
2004
Structure of the Earth
crust
mantle
inner core
outer core
1
3 of 20
32
© Boardworks Ltd 2005
2004
Tectonic plates
The Earth’s crust is made of sections called tectonic plates.
Where two plates meet is called a plate boundary.
Convection currents in the mantle plates move these tectonic
plates, which can move towards each other, move away from
each other and or move past each other.
1
4 of 20
32
© Boardworks Ltd 2005
2004
Plate boundaries 1 – sliding plates
Two plates can slide past each other, but this doesn’t always
happen smoothly. The large friction forces involved mean
that strain builds up and the plates move suddenly when the
strain gets too much.
plate A
plate B
This sudden movement of plates is called an earthquake
and it can be very destructive.
1
5 of 20
32
© Boardworks Ltd 2005
2004
Plate boundaries 1 – conservative boundary
1
6 of 20
32
© Boardworks Ltd 2005
2004
Why do earthquakes happen?
1
7 of 20
32
© Boardworks Ltd 2005
2004
Features of an earthquake
1
8 of 20
32
© Boardworks Ltd 2005
2004
Cross-section of the Earth – labels
Which part of this cross-section of the Earth should each
label point to?
crust
outer core
mantle
inner core
1
9 of 20
32
© Boardworks Ltd 2005
2004
Effect of an earthquake
An earthquake has occurred in the area shown in this picture.
If the plates moved in the directions indicated by the arrows,
what would the location would look like after the earthquake?

plate A
1
10ofof20
32
plate B
© Boardworks Ltd 2005
2004
Contents
Earth’s Structure
Earth and earthquakes
Seismic waves
More about plate boundaries
Continental drift
Summary activities
1
11ofof20
32
© Boardworks Ltd 2005
2004
Primary and secondary waves
During an earthquake there are two types of seismic waves
that are released from the epicentre. These are called
primary waves (P waves) and secondary waves (S waves).
Primary or P waves are the faster type of seismic waves.
They are longitudinal waves and when they hit the Earth’s
surface they make objects and buildings vibrate vertically.
P waves can travel through solids and liquids.
Secondary or s-waves are the slower type of seismic waves.
They are transverse waves and when they hit the Earth’s
surface they make objects and buildings vibrate horizontally.
S waves can only travel through solids.
1
12ofof20
32
© Boardworks Ltd 2005
2004
Effects of different seismic waves
P-waves arrive
first and shake
buildings
vertically.
This causes
little damage.
1
13ofof20
32
S-waves arrive
next and shake
buildings
horizontally.
This can cause
a lot of damage.
© Boardworks Ltd 2005
2004
Seismic waves inside the Earth
Waves within a layer
change direction
gradually because
there is a gradual
change in density.
S wave shadow
- only P waves
are detected in
this region.
earthquake
focus
At a layer boundary
there is a big change in
direction because there
is a big change in
density between layers.
1
14ofof20
32
© Boardworks Ltd 2005
2004
Words about seismic waves
epicentre
1
15ofof20
32
The faster type of seismic
wave, that is longitudinal
and makes buildings
vibrate up and down.
primary
waves
The location where the
shift in plates occurred
producing seismic waves.
secondary
waves
The slower type of seismic
wave, that is transverse
and makes buildings
shake from side to side.
© Boardworks Ltd 2005
2004
Comparing seismic waves
Complete this table comparing the properties of the two types
of seismic waves.
P wave
S wave
Type of wave
Speed
Media wave can
travel through
Damage caused
on Earth’s
surface
1
16ofof20
32
© Boardworks Ltd 2005
2004
Questions about seismic waves
mantle
wave A
wave B
outer core
1. What type of wave is wave A? How can you tell this?
2. Explain the path of wave B in terms of density.
3. What is the S wave shadow?
1
17ofof20
32
© Boardworks Ltd 2005
2004
Contents
Earth’s Structure
Earth and earthquakes
Seismic waves
More about plate boundaries
Continental drift
Summary activities
1
18ofof20
32
© Boardworks Ltd 2005
2004
Plate boundaries 2 – colliding plates
What happens at a plate boundary where an oceanic plate
and a continental plate collide?
The thinner, more dense oceanic plate is driven down into
the mantle. This is known as subduction.
thicker, less dense
continental plate
convection current
thinner, more dense
oceanic plate
convection current
melted oceanic plate
1
19ofof20
32
© Boardworks Ltd 2005
2004
Plate boundaries 2 – destructive boundary
1
20ofof20
32
© Boardworks Ltd 2005
2004
Plate boundaries 3 – plates moving apart
What happens at a plate boundary when oceanic plates
move apart due to convection currents in the Earth’s mantle?

oceanic plate
Magma moves
up to the
convection
surface, cools
current
and forms new
oceanic plate.
1
21ofof20
32
oceanic plate
convection
current

This is known
as sea-floor
spreading.
© Boardworks Ltd 2005
2004
Plate boundaries 3 – constructive boundary
1
22ofof20
32
© Boardworks Ltd 2005
2004
Words about plate boundaries
subduction
sea-floor
spreading
friction
1
23ofof20
32
The force that causes
earthquakes.
When an oceanic plate is
pushed down into the
mantle as it collides with
a continental plate.
When two oceanic plates
move apart to create new
crust.
© Boardworks Ltd 2005
2004
Contents
Earth’s Structure
Earth and earthquakes
Seismic waves
More about plate boundaries
Continental drift
Summary activities
1
24ofof20
32
© Boardworks Ltd 2005
2004
What is continental drift theory?
It is thought that all the continents were once joined together
in a huge supercontinent called Pangaea.
Over millions of years the continents drifted apart
because the tectonic plates they were on moved apart
due to convection currents in the Earth’s mantle.

1
25ofof20
32
© Boardworks Ltd 2005
2004
Continental drift theory animation
1
26ofof20
32
© Boardworks Ltd 2005
2004
Evidence for continental drift theory
There are a number of pieces of evidence to support the
theory of continental drift:
1. The shapes of the continents fit like a jigsaw.
2. The rock strata on separated continents are identical.
continent A
continent B
3. The fossil records on separated continents are identical.
1
27ofof20
32
© Boardworks Ltd 2005
2004
Contents
Earth’s Structure
Earth and earthquakes
Seismic waves
More about plate boundaries
Continental drift
Summary activities
1
28ofof20
32
© Boardworks Ltd 2005
2004
Glossary (1)
 continental drift – The theory that millions of years ago
all the continents formed a huge supercontinent and have
been slowly drifting apart ever since.
 core – The central region of the Earth below the mantle.
The outer part is liquid and the inner part is solid.
 crust – The thin, rocky, outer layer of the Earth.
 earthquake – A sudden movement of the Earth’s crust,
which causes vibrations that travel through the Earth.
 mantle – The layer of the Earth, between the crust and the
core, which is mostly solid rock that can flow very slowly.
 P waves – These are the fastest type of seismic waves.
They are longitudinal waves and can travel through solids
and liquids.
1
29ofof20
32
© Boardworks Ltd 2005
2004
Glossary (2)
 plate boundary – An area where two tectonic plates meet.
 S waves – These are the slowest type of seismic waves.
They are transverse waves and can only travel through solids.
 sea-floor spreading – This occurs under oceans where
plates move apart and magma rises to the surface and cools
to form new crust.
 seismic waves – Vibrations that travel through the Earth
as a result of an earthquake.
 subduction – This occurs where plates move together and
one of the plates is driven down into the mantle.
 tectonic plates – Large sections of the Earth’s crust and
upper mantle that move slowly over the surface of the Earth.
1
30ofof20
32
© Boardworks Ltd 2005
2004
Anagrams
1
31ofof20
32
© Boardworks Ltd 2005
2004
Multiple-choice quiz
1
32ofof20
32
© Boardworks Ltd 2005
2004