Download Unit 4

Unit 5
TECTONIC ACTIVITY
LEARNING AIMS
After studying this unit you should be able to:
1. explain what the theory of continental drift is about
2. describe what the earth is like inside
3. talk about processes involved in a volcanic eruption
KEY WORDS
continental drift, tectonic plate, plate boundary, crust, mantle, core, molten rock, friction, volcanic eruption,
earthquake
LEAD-IN
1.
2.
3.
What is the Ring of Fire?
How many tectonic plates are on earth?
How many active volcanoes are in the world?
EX 1 – In pairs or small groups, answer these questions.
1.
2.
3.
Why do the east coast of South America and the west
coast of Africa seem to fit each other?
As coal is formed from plants that need a warm
climate, why is there coal in an island near the Arctic?
Can volcanoes and earthquakes occur anywhere in the
world?
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Unit 5
EX 2 – Now skim this article and check your answers to the questions above.
Moving continents
A The belief that continents have not always been fixed in their present positions was first suggested
as early as 1596 by the Dutch map maker Abraham Ortelius. Ortelius suggested that the Americas were
‘torn away from Europe and Africa ... by earthquakes and floods’, and went on to say, ‘The vestiges of
the rupture reveal themselves if someone brings forward a map of the world and considers carefully the
coasts of the three [continents].’ However, it was not until 1912 that the idea of moving continents was
seriously considered as a full-blown scientific theory, when the theory of continental drift was
introduced in two articles by a 32-year-old German meteorologist named Alfred Lothar Wegener. He
contended that all the present continents used to form one ‘supercontinenť, which he called ‘Pangaea’
(the Greek for ‘all lands’ - the second syllable is usually pronounced ‘jee’ or ‘gay’), and that this began
to split apart around 200 million years ago.The parts drifted across the Earth, eventually breaking into
the various smaller continents that exist today.
B Wegener`s theory was based in part on what appeared to him to be the remarkable fit of the
South American and African continents, first noted by Ortelius three centuries earlier. Wegener was
also intrigued by the occurrences of unusual geologic structures and of fossils - of both plants and
animals - found on the matching coastlines of South America and Africa, which are now widely
separated by the Atlantic Ocean. He reasoned that it was physically impossible for most of these
creatures to have swum or have been transported across the vast ocean. To him, the presence of
identical fossils along the coastal parts of Africa and South America was the most compelling
evidence that the two continents were once joined.
C In Wegener`s mind, the drifting of continents after the break-up of Pangaea explained not only
the matching fossil occurrences but also the evidence of dramatic climate change on some
continents. For example, indications that there were once glaciers in regions of South Africa led to
the conclusion that this land must once have been situated much further away from the tropics.
Other mismatches of geology and present-day climate included the occurrence of coal - the product
of ancient temperate or tropical forests - in Spitzbergen, an island that is now close to the North
Pole.
D
At the time Wegener introduced his theory, the scientific community firmly believed the
continents and oceans to be permanent features on the earth`s surface. Not surprisingly, his proposal
was not well received, even though it seemed to agree with the scientific information available at the
time. A fatal weakness in Wegener`s theory was that it could not satisfactorily answer the most
fundamental question raised by his critics: what kind of forces could be strong enough to move such
large masses of solid rock over such great distances?
E After Wegener`s death in 1930, new evidence from ocean floor exploration and other studies
rekindled interest in his theory, ultimately leading, in the early 1960s, to the development of the theory
of plate tectonics.This scientific concept has revolutionised our understanding of the dynamic planet
upon which we live.The theory states that the earth`s outermost layer is fragmented into a dozen or more
plates of various sizes that are moving relative to one another as they ride on top of hotter, more mobile
material.
F The theory has provided explanations to questions that scientists had speculated upon for
centuries – such as why earthquakes and volcanic eruptions occur in very specific areas around the
world, and how and why mountain ranges like the Alps and Himalayas formed.
EX 3 – This is how
Pangaea may have
looked
around
225
million years ago. With
your partner, can you
identify the presentday continents and
sub-continents?
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Unit 5
EX 4 – Answer the questions below using no more than three words from the article for each
answer. Then compare your answers with your partner.
1. In Ortelius`s opinion, what caused continents to be separated?
2. In the theory of continental drift, what was given the name ‘Pangaea’?
3. Apart from shape and geological structures, what similar phenomena are found in South America and Africa?
4. What do indications of glaciers in South Africa and coal in Spitzbergen provide evidence of?
5. According to the 1960s theory, what does the top layer of the earth consist of?
6. What natural phenomena may have been created by movement on the earth`s surface?
EX 5 – You are going to hear a geography lecture about earthquakes and volcanoes.
The lecture is in two parts.
Part 1
First try and match the words below with their meanings. Cooperate with your partner. Then listen and check
your answers.
1 crust
a The place where two plates meet.
2 mantle
b A place a long way from a plate boundary where volcanoes happen.
3 core
c The layer of solid rock at the earth`s surface.
4 plate
d The layer of molten rock beneath the crust.
5 plate boundary e A piece of the earth`s crust.
6 hot spot
f The layers of liquid rock and solid iron at the earth`s centre.
Now read the questions below. Listen again and answer the questions with your partner. Make notes as you listen.
1. How thick is each of the earth`s layers? Describe each of these layers.
2. Explain why the plates move about.
3. Where are most earthquakes and volcanoes found?
4. Why are hot spots different from other volcanoes?
Part 2
Look at the diagram below. Two plates are mentioned on the recording. Listen and write their names in the
diagram.
Now draw arrows to show plate movements and put a circle round the zone of activity where there is friction,
earthquakes and melting of rock.
Listen again and sort the statements below into the correct order to show how volcanoes can happen at plate
boundaries.
• Molten rock rises.
• Friction melts the rock.
• Plates rub together.
• Volcanoes erupt on the surface.
• Plates move toward each other.
Work with your partner. Imagine you are a geography teacher and you want to explain how volcanoes can happen
at plate boundaries. Use the diagram above.
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Unit 5
EXTRA PRACTICE
EX 1 – Read the article “Moving continents” again. It has six paragraphs labelled A – F.
Which paragraph contains the following information? You may use any letter more than
once.
1. How later developments revived consideration of the theory of continental drift.
2. Evidence that some areas used to be situated in much warmer or cooler regions.
3. Something that Wegener`s theory could not explain.
4. A reason why living organisms can`t have moved from one continent to another.
5. An apparent contradiction in the reaction to the theory of continental drift.
6. An outline of a theory that explains how continental drift occurs.
EX 2 – Read this text about the effects of a volcanic eruption on the weather. Then
complete the summary below using words from the box. There are more words than you
need.
One of the most powerful volcanic eruptions ever recorded took place in 1815. In April of that year, Mount
Tambora, in what`s now Indonesia, erupted with catastrophic violence, ejecting over a million and a half tonnes of
ash, which darkened the sky over a radius of 500 kilometres. Much of it reached the upper atmosphere and
remained there for the next two years. To a considerable extent, this blocked solar radiation from reaching the
earth, significantly lowering temperatures, particularly in the northern hemisphere.
The following year, 1816, became known as ‘the year without a summer’. Southern Italy had the unusual
experience of seeing snowflakes, and the sun was masked by a cloud of what looked like smoke. During the spring
growing season, temperatures were abnormally low, and crops were ruined by hail and rain.
The resulting shortages made food very expensive across Europe, and thousands of people died of starvation.
There was social unrest, as the poor took to the streets, and high levels of violence.
In the north-eastern United States, the spring of 1816 arrived late and was exceptionally cold, with rain, frost and
snow continuing into June. Crops were destroyed, animals died, and tens of thousands of people were forced to move
to the richer soil and better growing conditions of the Midwest. So, indirectly, the volcanic eruption contributed to the
rapid settlement of this region.
Another side-effect of the eruption was that Mary Shelley wrote her novel Frankenstein when the bad weather forced
her to stay indoors during a holiday in Switzerland.
disease
storms
drought
sunlight
dust
floods
temperatures
hunger
ice
lava
migration
night
riots
snow
The eruption of Mount Tambora in 1815 filled the air with 1 …………………… The amount of
2.…………….. was reduced. The effects on the weather of 1816 included 3 ………………… in places where it
was a rare occurrence, and 4 ……………….that severely damaged crops. Many Europeans suffered from
5………………….., and there were serious 6…………………in many towns. In the USA there was
considerable 7………………….. from affected areas to the more fertile Midwest.
Mount Tambora today
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