Download 9 Geography Investigating Australia`s Physical Environments Term 1

9 Geography
Investigating Australia’s Physical Environments
Term 1 Week 4
ORIGINS OF THE CONTINENT – SCIENTIFIC PERSPECTIVE: CONTINENTAL DRIFT
Glossary
Define the following words in your exercise book:
Continental Drift, Tectonic plates, Fault mountains, Fold mountains, Tectonic processes, Core,
Mantle, Crust
Structure of the Earth:
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Outer.......................
Inner........................
Plate Tectonics
The Earth’s Surface or crust is split into a number of plates.
These plates fit together like a giant jigsaw puzzle. The plates float on semi-molten rocks of the
Earth’s mantle. Heating from the Earth’s core causes the semi-molten material in the mantle to
churn in currents. These currents, called convection currents, carry the crustal plates up to as much
as 15 centimetres per year.
The movement of the plates is known as the theory of continental drift. Scientists believe that about
225 million years ago all the continents were joined. Since then they have broken up and moved
apart to form the continents we know today.
9 Geography
Investigating Australia’s Physical Environments
Term 1 Week 4
Continental Drift
In the short term, it seems as though the continents are
stable, but the continents are mobile and have moved
around earth over millions of years. The Earth’s solid
outer crust is made up of a number of massive pieces –
called continental plates – that float on top of the
underlying mantle of liquid magma. The continents sit
on top of these continental plates. Currents in the
magma make the plates move
Do you think that they continents have always looked as they do now, of have they changed shape
or location throughout the Earth’s history?
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In early 1915, the German scientist Alfred Wegener developed a theory that the continents once
formed a giant supercontinent that he called Pangaea. He speculated that Earth took this form about
245 million years ago, during the Triassic period of the Mesozoic era. (The Mesozoic is the era in
which dinosaurs lived.) A few years after Wegener proposed his theory, South African geologist
Alexander Du Toit further theorized that Pangaea divided into two supercontinents 205 million years
ago. Du Toit called the northern supercontinent Laurasia and the southern one Gondwanaland.
9 Geography
Investigating Australia’s Physical Environments
Term 1 Week 4
P…………………………
L……………………….
&
G…………………………………
Proposed by ……………………
Proposed by ……………………
Fold Mountains
Most of the world’s great mountain regions are formed when
crustal rocks buckle as one plate slides under another
(subduction). Some of the crust is forced down and becomes
part of the magma; other rocks are forced upwards and bent or
folded.
Fault Mountains
Faulting occurs when rocks crack and sections move up or
down. This process forms both mountains and rift valleys.
Rocks behave differently under pressure, depending on
how brittle they are. Rocks close to the surface tend to be
more brittle and will snap under pressure. Faults are
formed when these rocks break.
Evidence for Continental Drift and Plate Tectonics
Many fossils have been found which link continents together and support the idea that the
continents were once joined together. They show that a plant or animal lived on the edge of two (or
more) continents. This shows that the two areas would have had to have a similar climate (and so a
similar latitude and longitude). An example is Antarctic Beech.
Fossil evidence has also shown that areas of land which were previously underwater or at least at a
low altitude have been uplifted. Fossil seashells have been found high in the Himalayas. The highest
mountain range on Earth was under the sea until about 30 million years ago, when India collided
with Asia and the rocks were thrust upwards to form the Himalayas.
There is a continuous system of large ridges located some distance from the continents, often in
mid-ocean. There are also deep open trenches at many places in ocean floors. These provide
evidence of plate movement together (ridges) and apart (trenches). This theory has been confirmed
by paleomagnetism and core sampling.
9 Geography
Investigating Australia’s Physical Environments
Term 1 Week 4
Questions:
How are plate tectonics and continental drift related?
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What is subduction, and how does it relate to the formation of mountains?
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Unscramble the following words:
daonawng
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sgredi
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ecro
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atlfu
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ontnecnit
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lodf
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telamn
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tcincote
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alestp
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tploygoenloa
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ocvnceitno ctesnurr
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lontem atimlare
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niod-urtlanaias tlaep
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Homework: Internet research (due next lesson)
 What did Alfred Wegener propose in 1912?
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 What does Pangea mean?
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 When did Pangea start breaking up?
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 What paleontological observations supported Wegener’s theory?
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