sd3_cb_ans_05

advertisement
Answers to coursebook questions
5: The fragile crust
Unit 5.1
1 a
False: Triassic reptiles could not have swum the distances required to populate
different continents.
b True: There are similar mountain ranges in the USA and Europe, and also in
Africa and South America.
c False: Many of the continents that do not have glaciers now were once cold
enough to have them.
d True: Coal deposits above the Arctic Circle suggest the land has floated there
from warmer climates.
e False: The rock of the ocean floor is much younger than that of the continents.
f False: Continental rock is less dense than the rock of the ocean floor and floats
on it.
g True: Magnetic stripes on the ocean floor suggest that new rock is made along
mid-ocean ridges.
2 Six pieces of evidence that suggest the continents were once joined are: the shape of
the continents; fossil remains of the same fern-like plants and Triassic reptiles; rock
formations in mountains on different continents; ancient glaciers; coal above the
Arctic Circle; and magnetism in ancient rocks.
3 a Gondwana: Australia, Antarctica, South America, Africa, India
b Laurasia: North America, Europe, most of Asia
4 The evidence that Australia once was far colder than it is now: valleys made by
glaciers; the remains of a small dinosaur called Leaellynasaura found near Apollo
Bay which had larger-than-normal optic lobes allowing it to see in the 24-hour
darkness of an Antarctic winter.
5 Five surprising facts about the ocean floor when it was first mapped were: huge
volcanic mountain ranges exist down the centre of the oceans; the rock of the ocean
floor is much younger than that of the continents; deep ocean trenches exist; the
rock of the continents is less dense than that of the ocean floor; the ocean floor has
magnetic stripes that indicate that the rock is of different ages.
6 The longest mountain range in the world is the Mid-Atlantic Ridge, being
65 000 km long.
7 The ocean floor often has magnetic stripes because as the lava flows out of the midocean ridge it cools and solidifies; it adopts the magnetism of the Earth at that
moment; the magnetic field of Earth changes every now and then, forming ‘stripes’
of magnetism.
8 The rock of the ocean floor is like a conveyor belt in that it forms new rock at the
mid-ocean ridge and then transports it over many years into the trench and
subduction zone formed where the ocean plate hits and dives under the continental
plate.
© Pearson Education Australia (a division of Pearson Australia Group Pty Ltd) 2006.
This page from the Science Dimensions 3 Teacher’s Edition CD may be photocopied for classroom use.
Answers to coursebook questions
5: The fragile crust
9 a
Tectonic plate: sheet of crust, partly molten bottom and top—layer of mantle
that all shifts as one
b Mantle: molten rock under intense pressure and temperature—the layer under
the crust
c Crust: Thin layer of solid rock that we live on—the ‘skin’ of the Earth
10 The crust is 8 to 64 km thick.
11 The oldest rocks on the ocean floor are those closest to the trenches and the
youngest are next to the ridges.
12 Convection currents are caused by hot material rising and cooler material dropping.
13 Convection currents can take millions of years to cycle around the mantle.
14 The mantle is kept hot because the crust traps heat like a blanket; patches are
continually being heated by radioactive decay of uranium, thorium and potassium.
15 The theory of plate tectonics suggests that the Earth’s crust is made from a series of
rock plates that shift around on convection currents in the mantle.
16 The temperatures along the ridges are higher than elsewhere in the ocean because
this is where magma emerges and cools to become solid rock. This hot lava will heat
the water around it.
17 It would be impossible for coal to form in the Arctic or Antarctic now because it is
too cold there for the plants that make up coal to grow.
18 Diagrammatic answer required
19 Smoke rises up a chimney on a rising, hot, convection current of air warmed by the
fire.
20 If the mantle cooled and became solid, the plates would stop moving.
21 Another possible reason why Australia doesn’t have any glaciers now could be
global climate change raising the temperature of the whole planet. Hence, Australia
could still be in the same position, but the climate would be too warm for glaciers to
exist.
22 If an average lifetime is 80 to 100 years, then the plate on which Australia sits will
move northward at between 5 × 80 = 400 cm to 5 × 100 = 500 cm per year. This is
equivalent to 4 to 5 metres.
Unit 5.2
1 a transform or scraping
b spreading
c collision
2 a conservative: transform or scraping (a)
b destructive: collision (c)
c constructive: spreading (b)
© Pearson Education Australia (a division of Pearson Australia Group Pty Ltd) 2006.
This page from the Science Dimensions 3 Teacher’s Edition CD may be photocopied for classroom use.
Answers to coursebook questions
5: The fragile crust
3 A fault is a weakness in the Earth’s crust.
4 A rift valley is the crack or valley caused by a fault.
5 Examples of rift valleys: East African Rift Valley, the Jordan Rift Valley holding
the Sea of Galilee, Dead Sea and Gulf of Aqaba.
6 The mid-ocean ridge constantly tries to heal itself, forming a ‘rock scab’ that is the
ridge itself. Magma keeps breaking through the scab, however, oozing out and
forcing the repair to happen all over again.
7 a faster
b heavier
c ocean plate
8 A subduction zone is where one plate (usually the ocean plate) dives another
(continental) plate. Friction causes earthquakes along it and melts the rock. The
molten rock may have enough pressure to break the surface to form volcanoes.
9 The deepest underwater trench is the Mariana Trench, located in the western Pacific
Ocean. Its depth is 11 033 m.
10 Island chains created by the collision of two ocean plates: the islands of Japan,
Indonesia, the Philippines, the Caribbean and the Aleutians.
12 The Andes Mountains lie parallel to the Peru-Chile trench.
13 At a scraping or transform boundary, plates scrape along each other. These don’t
make mountains or volcanoes but do produce lots of earthquakes, some very strong.
Although most of these boundaries are underwater, some are on land.
14 A major transform boundary is the San Andreas fault, which runs 1300 km through
California, USA, directly under San Francisco and close to Los Angeles (often
called LA).
15 a rock L
b rock E
c rock J
16 a
b
c
d
e
f
g
collision
spreading
collision
collision
collision
scraping
collision
17 a
b
c
d
e
spreading
transform
spreading
collision
spreading
© Pearson Education Australia (a division of Pearson Australia Group Pty Ltd) 2006.
This page from the Science Dimensions 3 Teacher’s Edition CD may be photocopied for classroom use.
Answers to coursebook questions
5: The fragile crust
f
spreading
18 Diagrammatic answer required
19 a
b
c
d
e
f
g
h
Himalayas: Indo-Australian plate with Eurasian plate
Andes: South American plate with Nazca plate
Mid-Atlantic Ridge: African plate with South- and North-American plates
Caribbean islands: North American plate with Caribbean plate
Japan: Pacific plate with Eurasian plate
Mariana Trench: Philippine plate with Pacific plate
San Andreas fault: Pacific plate with North-American plate
Dead Sea: Indo-Australian plate with African plate
20 Assuming an average lifetime of between 70 and 90 years, the Himalayas will grow
between 70 and 90 centimetres. If you reach 100, they will have grown 1 metre.
21 a A further 10 m will take 1000 years.
b A further 100 m will take 10 000 years.
c A further 1 km (1000 m) will take 100 000 years.
Mediterranean Sea: the Red Sea needs to widen another 260 km (500 – 240 km).
260 km = 26 000 000 cm. So the time taken would be: 26 000 000/20 =
1 300 000 years = 1.3 million years.
b Atlantic Ocean (6100 km): time = 29 300 000 years = 29.3 million years
c Pacific Ocean (14 000 km): time = 68 800 000 years = 68.8 million years
22 a
Unit 5.3
1 The friction between the plates is normally enough to stop movement of the plates
for a while. The plates are still pushing, however, and the pressure will build until it
overcomes the friction. That’s when the plates will move, suddenly.
2 The deepest the focus can be below the surface is 200 km.
3 A seismometer detects an earthquake. The graph it produces is called a seismograph.
4 Body: Primary (P) and secondary (S)
Surface waves: Rayleigh (R) and Love (L)
5 Refraction is what happens to waves as they change speed on entering a new
material.
6 Different densities and temperatures of the rock below the surface cause changes in
speeds of P and S waves and cause them to be bent or refracted.
7 S waves apparently do not pass through the Earth’s core since there is always a
‘shadow’ opposite the epicentre. S waves cannot pass through liquid, indicating that
the outer core must be liquid.
8 A single seismograph tells us how far away a quake is but gives no information
about its direction.
© Pearson Education Australia (a division of Pearson Australia Group Pty Ltd) 2006.
This page from the Science Dimensions 3 Teacher’s Edition CD may be photocopied for classroom use.
Answers to coursebook questions
5: The fragile crust
9 Scientists can predict how far an earthquake is away from them by measuring the
time difference between the arrival of the P and the S waves from an earthquake.
10 The two surface seismic waves are Rayleigh (R) and Love (L) waves.
11 Diagrammatic answer required
12 a
Body waves travel through the body of the Earth, while surface waves travel the
longer distance across the surface.
b The focus is the point underground where the quakes starts. It is the point of
slippage. The epicentre is the place on the surface directly above it.
c A longitudinal wave is a ‘push-pull’ wave, and moves particles back and forth in
the direction of the movement of the wave. A transverse wave is an ‘up-down’
wave that moves particles at right angles, or sideways, to the direction of the
movement.
13 a P waves, sound
b S and L waves, water waves, light
14 Diagrammatic answer required
15 a
b
c
d
e
f
g
h
i
L (and sometimes R)
S and L
P
P and S
P
L
R
R
S and L
16 The branch bends and stores a lot of energy. It gets to a point where it suddenly
breaks, releasing all of this stored energy suddenly. Earthquakes move and bend
rock and store energy as they do. They release all that energy when the quake
occurs, just like the broken branch.
17 All of Australia sits on the Indo-Australian plate. There are no major boundaries
running through it. Papua New Guinea and New Zealand both straddle the IndoAustralian and Pacific plates and sit on a boundary where earthquakes can be
expected.
18 a
b
c
d
2500 km
1300 km
2150 km
6350 km
19 If P and S waves arrive at the same time then you must be at the epicentre of the
quake (actually, you must be at the focus itself!).
20 a 7.8 min or 7 min 48 s
b 2.6 min or 2 min 36 s
© Pearson Education Australia (a division of Pearson Australia Group Pty Ltd) 2006.
This page from the Science Dimensions 3 Teacher’s Edition CD may be photocopied for classroom use.
Answers to coursebook questions
5: The fragile crust
c 5 min
d 1.6 min or 1 min 36 s
21
Arrival time
of P waves
(h:min:s)
10:24:00
Arrival time
of S waves
(h:min:s)
10:32:00
Time
difference
(min:s)
8:00
Time (min)
Distance of
epicentre (km)
8.0
6200
04:48:20
4:52:50
4:30
30 ÷ 60 = 0.5
so time is 4.5
min
2900
2:55:21 p.m.
3:01:21 p.m.
6:00
6.0
4150
7:37:03 p.m.
7:42:33 p.m.
5:30
5.5
3700
14:08:34
14:11:46
3:12
3.2
1950
20:21:02
20:25:50
4:48
4.8
3150
05:45:10
05:50:10
5:00
5.0
3300
11:28:00
11:34:30
6:30
6.5
4650
08:08:56
08:12:56
4:00
4.0
2500
15:21:04
15:28:40
7:36
7.6
5800
22 a
The tectonic plates involved in the earthquake that triggered the 2004 Boxing
Day tsunami were Eurasian and Indo-Australian plates.
b The earthquake occurred at a collision boundary.
Unit 5.4
1 Three types of faults are normal, revere and transcurrent.
2 Diagrammatic answers required
3 If the rock that makes the fault scarp is hard, it will weather slowly. If soft, it will
weather quickly and will be carried away by erosion, leaving a rounded rise instead.
4 Australian examples of horst and graben are the Spencer and St Vincent gulfs in
South Australia.
5 Loch Ness is a Scottish lake that has filled part of a transcurrent fault.
6 A substance shows plastic behaviour if it can bend and fold without breaking.
7 Rock can act in a plastic way if it is under extreme pressure and temperatures,
typically found in folding.
8 Diagrammatic answer required
9 It is evident that the Himalayas were once below the sea because fossilised seashells
have been found high on Mt Everest.
© Pearson Education Australia (a division of Pearson Australia Group Pty Ltd) 2006.
This page from the Science Dimensions 3 Teacher’s Edition CD may be photocopied for classroom use.
Answers to coursebook questions
5: The fragile crust
10 Diagrammatic answer required
11 An igneous intrusion is solid rock formed when magma has cooled and solidified
below ground.
12 Hot spots are located under the Hawaiian islands (Pacific Ocean), Yellowstone
National Park (USA), Reunion Island (Indian Ocean), the Azores, the Canary
Islands, Cape Verde, Ascension Island, St Helena, Tristan de Cunha, Gough Island
and Bouvet Island (all in the Atlantic Ocean) and under Bass Strait.
13 The Hawaiian Islands in order from youngest to oldest: Hawaii, Maui, Oahu, Kauai
14 If the magma at a hot spot boils underground water, it can then force its way to the
surface as geysers, steaming lakes and mud pools.
15 Examples of fossils fuels: oil, petrol, kerosene, natural gas, coal
16 Intense heat and pressure is needed to convert kerogen into hydrocarbons. Weak
spots can provide these conditions. The other idea is that oil and gas would be
squeezed into the more porous rock that weak spots would provide.
17 Kerogen is a tar-like substance made from decomposed plant and animal matter. A
hydrocarbon is the actual chemical energy store in fossil fuel and is thought to have
come from ‘cooking’ kerogen.
18 Shaking a can of soft drink builds up pressure in it. When its top is popped the
pressure is suddenly relieved by spraying liquid out from its top. A composite
volcano does something similar. Pressure builds until it ‘pops’ its top, spraying lava
and ash everywhere.
19 Diagrammatic answer required
20 The mountains and volcanoes of New Zealand are both caused by the collision of
the Pacific with the Indo-Australian plates. Mountains have buckled up and
volcanoes have formed from the subduction zone.
21 Evidence that the Hawaiian Islands are moving westwards: the oldest island Kauai is
in the far west; the youngest Hawaii is in the far east; a new underwater volcano,
Loihi, is forming east of Hawaii; volcanic activity is only under Hawaii and Loihi.
22 The natural gas reserves of Bass Strait would be expected to be about longitude
40S due to the weakness caused by a hot spot. Because the Indo-Australian plate is
moving north the reserves may be a little north of 40S.
23 a Diagrammatic answer required
b Layer K was laid down first, followed by J, I, H, G, F, E and D on top. All were
laid flat. Pressure folded the layers upwards, forming an upward fold or
anticline. Erosion removed the top of the fold, until D and E were nearly worn
away. The erosion left the surface flat once more. Sediment laid new layers: C
first, then B and A on top.
© Pearson Education Australia (a division of Pearson Australia Group Pty Ltd) 2006.
This page from the Science Dimensions 3 Teacher’s Edition CD may be photocopied for classroom use.
Answers to coursebook questions
5: The fragile crust
Chapter review
1 A map of the world in the future will be different from what it is now because all of
the plates and their continents are shifting. Some will join, others will part, some
will slide along each other.
2 The mysteries of the ocean floor were discovered only in the 20th century with the
invention of sonar and the need for good ocean-floor maps in World War II.
3 a
The north poles of ancient rocks that are magnetic all point in different
directions. When the continents are pieced together the north piles all point in
the same direction, suggesting the continents have shifted and twisted.
b Magnetic stripes exist parallel to the mid-ocean ridges. The stripes closest to the
ridges are the newest and the ones further out are older, suggesting that they are
moving away from the ridges and towards the trenches.
4 Convection currents push the rock of the mantle around. The bottoms of the plates
are partially molten or ‘soggy’ and will be carried with the mantle as it moves
underneath them.
5 Magma is molten rock full of gas (mainly steam). Its density is less than the
surrounding rock and so it will push upwards through the covering tectonic plate.
6 The ocean floor is like a conveyer belt as it carries the newly created rock from the
mid-ocean ridges across the ocean towards the trenches.
7 The longest mountain ridge (about 65 000 km long) is down the middle of the
Atlantic. The highest is the Himalayas on the border of India and China/Tibet.
8 Dense materials sink and lighter materials float. The rock of the continental plates is
less dense than the rock of the ocean plates. The continents thus will ‘float’ on the
ocean floor, and the ocean plate will sink under the continent.
9 Plate boundaries are where plates separate, collide or scrape over each other.
Friction will occur and will stop movement until the pressure is sufficient to
overcome the friction. When it does, the plate slips and an earthquake results.
10 The subduction zone is completely molten 200 km below the surface.
11 Primary, secondary, Raleigh and Love waves are all detected by the seismometer.
They are in the order P first, S next and R and L basically together and last.
12 Diagrammatic answer required
13 a S and L
b P
c R
14 Diagrammatic answer required
15 Three different ways mountain ranges can form are: continent/continent collision,
forming folded mountains; volcanic action at plate boundaries or hot spots; normal
faults create horst and graben which can erode into mountain ranges and basins.
© Pearson Education Australia (a division of Pearson Australia Group Pty Ltd) 2006.
This page from the Science Dimensions 3 Teacher’s Edition CD may be photocopied for classroom use.
Answers to coursebook questions
5: The fragile crust
16 A fault is a weak spot or break in the crust along which the crust can move in an
earthquake. There is no break in the crust when folded. The crust buckles instead of
breaking and shifting.
17 A cinder cone has steeper sides than a shield volcano because it is simply a pile of
rock. The pile will build until the rock begins to tumble further down the slopes. A
shield volcano is made from cooled lava. Being molten it will spread further than
solid rock.
18 The mantle is solid but still able to move due to the extreme pressures and
temperatures there. Other ‘solid’ substances that can ‘move’ are plasticine, clay and
mud.
19 The Earth is like toast on soup in that both have slabs of moving solid crust floating
on a hot, thick liquid.
20 All the current continents were part of Pangaea. Hence, it is literally all the lands. Its
‘babies’ are Gondwana and Laurasia.
21 The theory of continental drift assumes that only the continents are shifting. The
theory of plate tectonics involves much larger slabs of rock (which also carry the
shifting continents).
22 The temperature near the ceiling of a room is always hotter than at floor level
because of convection currents. The warmer air rises and the cooler air drops: the
temperature will increase as you go higher in the room.
23 One easy way of remembering what P, S, R and L waves do is P = push/pull, S =
shake, R = roll, L = leftovers!
© Pearson Education Australia (a division of Pearson Australia Group Pty Ltd) 2006.
This page from the Science Dimensions 3 Teacher’s Edition CD may be photocopied for classroom use.
Download