Download C1b 6.2 The Restless Earth

The Changing World
The Restless Earth
Tectonic plates
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The crust is made of about twelve plates.
These are like big rafts floating on the semi-molten
mantle.
Convection currents within the mantle cause the
plates to move.
Although they only move about 2 cm/year this can
have huge effects over long periods of time.
Sea floor spreading
When two oceanic plates move apart
molten rock rises to the surface.
sea floor spreading
oceanic plate
magma rising
Continental Drift
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On average, the plates only drift
about 2cm/year. However 2cm
multiplied by a million is a long way!
Scientists think the continents were
originally all together in a supercontinent called Pangaea.
Over millions of years they have
drifted to their present positions on
the floating tectonic plates.
Pangaea
Millions
of years
Continental Drift
Evidence for Continental Drift
The theory is supported by several
pieces of evidence.
For example, if we consider Africa and
South America there is:
– The “jig-saw fit”
– The similarities in the rock layers
from Africa and South America.
– Similarities in the type and age of
fossils.
– Evidence of related species that
definitely did not swim the Atlantic
Ocean!
Jig Saw fit
Similar rocks
and fossils
How does it work?
• How do convection currents
actually work?
• Place potassium permanganate
crystals at bottom of beaker of
water
• Start to heat water with
bunsen
• Diagram in book of what
happens
Plate boundaries
What happens when plates meet
• Constructive plate boundary – new ocean floor
is created
• Destructive plate boundary – oceanic plates
slide under continental plates – subduction
• Conservative plate boundary – plates slide past
each other - Earthquakes
Effects at Plate Boundaries
When a continental plate and an oceanic plate
meet, the effects include:
plates juddering past each other producing earthquakes
the continental plate buckles upwards whilst the
oceanic plate subducts (goes underground)
volcanoes result from the
rising magma (melted
oceanic plate)
volcano
oceanic
plate
magma rising
continental plate
Activity
• Find the words and
write a sentence
about how each one
has something to do
with plate tectonics.
– Drift
– Earthquake
– Fossil
– Jigsaw
– Magma
– Pangaea
– Plates
– Subduct
– Volcano
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Rocks
Types of rocks
There are three main types of rocks:
1.Igneous - formed when molten rock cools.
2.Sedimentary – formed by the “cementing together”
of small grains of sediment.
3.Metamorphic – rocks changed by the effect of heat
and pressure.
All of these are involved in a continuous flow of rock from
the surface underground only to emerge again later as part
of the on-going rock cycle.
Igneous rocks
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These are rocks formed by the cooling of molten
rock (magma.)
Magma cools
and solidifies
forming
igneous
rocks.
volcano
magma
Types of igneous rocks
Igneous rocks divide into two main groups:
– Intrusive igneous
– Extrusive igneous.
• Intrusive igneous
rocks, like granite,
are formed when
magma solidifies
within the ground.
• Extrusive igneous
rocks, like basalt,
are formed when
magma solidifies
above the ground.
Igneous rocks and crystal size
The more slowly a rock changes from liquid to solid the
bigger the crystals grow.
Intrusive igneous rocks,
like granite, usually have
clearly visible crystals.
Intrusive igneous
rocks that cool
really slowly can
have very big
crystals.
Extrusive igneous rocks,
like basalt, have crystals
that are usually small.
Extrusive igneous
rocks that cool
really quickly can
have a glassy
appearance.
Chemical and Physical Weathering
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Surface rocks seem to be gradually reduced in size by
weathering processes.
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Chemical weathering is when chemicals, such as those
in acid rain, ‘eat’ away certain rocks.
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Physical weathering is to do with the rocks being broken
down by the action of wind, rain and sun. For example,
during the freezing and thawing of water in the cracks of
rocks, the expansion of water makes the rocks splinter.
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The small broken fragments wash into rivers and,
eventually, reach the sea where they settle as sediment.
Sedimentary rocks
Sedimentary Rocks are rocks formed when particles
of sediment build up and are “cemented together”
by the effect of pressure and minerals.
Fragments washed to the sea
Rocks are broken
up by the action
of weather
sea
Sedimentary
rocks
Sedimentary rocks
Sedimentary Rocks tend to have visible grains of sediment.
Sometimes they contain fossils.
They are usually softer than igneous rocks.
Examples of sedimentary rocks are sandstone and mudstone.
Getting older
Sandstone is
formed from the
cementing
together of
grains of sand.
Metamorphic rocks
Metamorphic rocks are formed by the effect of heat
and pressure on existing rocks.
This can greatly affect the hardness, texture or layer
patterns of the rocks.
Pressure from
surface rocks
metamorphic
rock
Magma
heat
forming
here
Metamorphic rocks
Marble, slate and schist are metamorphic.
– Limestone is a rock often formed from the
sediment of shells. Temperature and pressure
cause the rock to reform as small crystals that
are much harder. It is used as a hard and
decorative stone in buildings, sculptures etc.
– Slate is formed when pressure squeezes
mudstone into plate like grey sheets. It is used in
roofing.
– Schist and mica are formed when mudstone is
subjected to very high temperatures as well as
pressure. Again they contain layers which is
typical of many (not all) metamorphic rocks.
Activity
Match the rock with the correct description.
Give an example of this type of rock.
Rock type
Description
intrusive
igneous
Large crystals, hard rock
metamorphic
Sandy texture, soft rock
extrusive
igneous
Small crystals, hard rock
sedimentary
Wavy layers of crystals
The rock cycle
Activity
Crack the code! What should this really say?
•
Weathering
(Giant
hewer) leads to fragments collecting in the
sea and forming (amsedimentary
seen dirty) rocks such as
mudstone
sandstone
chalk, (sum
to end) and (and
so nest).
•
pressure
metamorphic
Heat and (perusers)
can lead to (a chem
import)
rocks such as (stale)
and (ambler).
slate
marble
•
Some of these will melt and eventually cool as
intrusive
they approach the surface to form (I ruin
vets)
(goigneous
in use) rocks such as (get
rain).
granite
What gases would have formed the original
atmosphere around planet Earth?
1.
2.
3.
4.
Hydrogen and helium
Oxygen and nitrogen
Methane and ammonia
Carbon dioxide and water
What gases form the majority of the present
atmosphere around planet Earth?
1.
2.
3.
4.
Hydrogen and helium
Oxygen and nitrogen
Methane and ammonia
Carbon dioxide and water
What gas protects us against dangerous UV
radiation?
1.
2.
3.
4.
Sulphur dioxide
Nitrogen oxide
Methane
Ozone
What gas is a major cause of the greenhouse
effect?
1.
2.
3.
4.
Sulphur dioxide
Nitrogen oxide
Carbon dioxide
Chlorine dioxide
What process increases atmospheric carbon
dioxide levels?
1.
2.
3.
4.
Photosynthesis
Respiration
Formation of Fossil fules
Formation of carbonate rocks
What layer of the Earth is around 50Km thick
and high in silicon and oxygen?
1.
2.
3.
4.
Inner core
Outer core
Mantle
Crust
What layer of the Earth is mostly molten iron
and nickel?
1.
2.
3.
4.
Inner core
Outer core
Mantle
Crust
What layer of the Earth is made of viscous
semi-molten magma?
1.Inner core
2.Outer core
3.Mantle
4.Crust
What type of rock is formed by solidification of
molten magma?
1.
2.
3.
4.
Igneous
Metamorphic
Sedimentary
Fossilised
What type of rock is formed by cementation of
small particles of weathered rock?
1.
2.
3.
4.
Igneous
Metamorphic
Sedimentary
Fossilised
What type of rock is formed by the effect of heat
and pressure upon other rocks?
1.
2.
3.
4.
Igneous
Metamorphic
Sedimentary
Fossilised
What type of rock is least likely to contain
fossils?
1.
2.
3.
4.
Igneous
Metamorphic
Sedimentary
Fossilised
What is the process where tectonic plates
separate and magma creates new solid crust?
1.
2.
3.
4.
Weathering
Ageing
Sea floor spreading
Sedimentation
What is the process where tectonic plates move
gradually apart?
1.
2.
3.
4.
Continental breakfast
Continental drift
The rock cycle
Subduction
Which of these is not evidence for continental
drift theories?
1.
2.
3.
4.
Similarities of fossils
Similarities of rock layers
Jig-saw fit of coastal shapes
Similarities of climate