Transcript KS4 Earth`s Structure 4992KB

KS4 Physics
Earth’s Structure
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Contents
Earth’s Structure
Earth and earthquakes
Seismic waves
More about plate boundaries
Continental drift
Summary activities
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Structure of the Earth
crust
mantle
inner core
outer core
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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.
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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.
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Plate boundaries 1 – conservative boundary
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Why do earthquakes happen?
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Features of an earthquake
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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
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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
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plate B
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Contents
Earth’s Structure
Earth and earthquakes
Seismic waves
More about plate boundaries
Continental drift
Summary activities
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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
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Plate boundaries 2 – destructive boundary
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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.
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oceanic plate
convection
current

This is known
as sea-floor
spreading.
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Plate boundaries 3 – constructive boundary
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Words about plate boundaries
subduction
sea-floor
spreading
friction
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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.
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Contents
Earth’s Structure
Earth and earthquakes
Seismic waves
More about plate boundaries
Continental drift
Summary activities
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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.

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Continental drift theory animation
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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.
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Contents
Earth’s Structure
Earth and earthquakes
Seismic waves
More about plate boundaries
Continental drift
Summary activities
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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.
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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.
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Anagrams
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Multiple-choice quiz
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