1. A/Prof. Orsola De Marco 9850 4241 orsola.demarco@mq.edu.au
ASTR178 Other Worlds
A/Prof. Orsola De Marco

2. Help questions (For this week)
Announcements
Website of the book. It contains many articles and links:
Help questions (For this week)
What does the word Moon mean?
1-28, page 232, 233.
Most of the questions in this chapter are relevant since I covered this chapter pretty thoroughly.

3. The Moon Practical All instructions have been posted on the website.
Download the instructions and the sky chart.
Go out at least 5 times between 14 August and 27 August ~8-9PM.
Plot the Moon position on the Sky Chart provided, including the Moon’s phase.
Always go out at the same time for instance sometime between 8 and 9 pm. IF YOU DO NOT THE EXPERIMENT WILL NOT WORK.
Answer the questions.
Return the work to the boxes by September 17.

4. How to use a Sky Chart

5. In last class
A quick wrap up of the magnetic fields in the Solar System.
Earth’s energy sources
The Greenhouse effect
Earth’s inner layers (we started it, we will finish in this class).
What does the word Moon mean?

6. In this class Earth’s inner layers Plate tectonics
A few rock definitions
Earth’s early atmosphere and the rise of oxygen
Earth’s current atmosphere, temperature, pressure and circulation.
The Human effect on the atmosphere and climate.
We started talking about the moon, but this will be the subject of Week 4, Class 1.
What does the word Moon mean?

7. Figure 9-7 Chemical Differentiation and the Earth’s Internal Structure
(a) The newly formed Earth
was molten throughout its volume. Dense
materials such as iron (shown in orange) sank
toward the center, while low-density materials
(shown in blue) rose toward the surface.
(b) The present-day Earth is no longer completely molten
inside. A dense, solid iron core is surrounded by a
less dense liquid core and an even less dense
mantle. The crust, which includes the continents
and ocean floors, is the least dense of all; it floats
atop the mantle like the skin that forms on the
surface of a cooling cup of cocoa.

8. Figure 9-8 Seismic Waves
Earthquakes produce two kinds of waves
that travel through the body of our planet. One kind, called P
waves, are longitudinal waves. They are analogous to those produced by
pushing a spring in and out. The other kind, S waves, are transverse
waves analogous to the waves produced by shaking a rope up and down.

9. Richard Dixon Oldham (Irish) 1858-1936
Hypothesized the existence of a molten core.
Figure 9-9 The Earth’s Internal Structure and the Paths of Seismic Waves
Seismic waves follow curved paths because of differences in the density
and composition of the material in the Earth’s interior. The paths curve
gradually where there are gradual changes in density and composition.
Sharp bends occur only where there is an abrupt change from one kind of
material to another, such as at the boundary between the outer core and
the mantle. Only P waves can pass through the Earth’s liquid outer core.
Inge Lehmann (Danish)
Hypothesized the existence of the inner core

11. Figure 9-10 Temperature and Melting Point of Rock Inside the Earth
The temperature (yellow curve) rises steadily from the Earth’s surface to its center.
The melting point of the Earth’s material (red curve) is also shown on this
graph. Where the temperature is below the melting point, as in the mantle and
inner core, the material is solid; where the temperature is above the melting
point, as in the outer core, the material is liquid. (Adapted from T. Grotzinger,
T. H. Jordan, F. Press, and R. Siever, Understanding Earth, 5th ed., W. H. Freeman, 2007)

12. Plate tectonics Alfred Wegener (German) 1880-1930
Figure Fitting the Continents Together
Africa, Europe, Greenland, North America,
and South America fit together remarkably well. The fit is especially convincing
if the edges of the continental shelves (shown in yellow) are used, rather than
today’s shorelines. This strongly suggests that these continents were in fact
joined together at some point in the past. (Adapted from P. M. Hurley)
Weneger had the original idea (1912) but lacked a good mechanism for plate tectonics. Arthur Holmes had the idea (in the 1930s)that this was the convective motion of the mantle.
Arthur Holmes (British)

13. Roethosaurus – Early-mid Jurassic From Queensland!
Figure The Breakup of the Supercontinent Pangaea
(a) The shapes of the continents led Alfred Wegener to conclude that more than 200 million
(2x108) years ago, the continents were merged into a single
supercontinent, which he called Pangaea. (Adapted from F. Press, R. Siever, T. Grotzinger,
and T. H. Jordan, Understanding Earth, 4th ed., W. H. Freeman, 2004)
Roethosaurus – Early-mid Jurassic
From Queensland!

14. Figure 9-12 The Breakup of the Supercontinent Pangaea
(b) Pangaea first split into two smaller land masses, Laurasia and Gondwana. (Adapted from F. Press, R. Siever, T. Grotzinger,
and T. H. Jordan, Understanding Earth, 4th ed., W. H. Freeman, 2004)

15. Figure 9-12 The Breakup of the Supercontinent Pangaea
(c) Over millions of years, the continents moved to their present-day locations. Among the evidence
confirming this picture are nearly identical rock formations 200 million
years in age that today are thousands of kilometers apart but would have
been side by side on Pangaea. (Adapted from F. Press, R. Siever, T. Grotzinger,
and T. H. Jordan, Understanding Earth, 4th ed., W. H. Freeman, 2004)

16. Tectonic activity is cyclic
What we know of the tectonic movement (Pangaea to today) lasted ~200 million years.
Before then another cycle had taken place. The supercontinent before Pangaea was named Rodenia ( million years ago).
Tectonic activity has a ~500 million year “cycle”.
“Pangaea Ultima” a possible next supercontinent
science-at-nasa/2000/ast06oct_1/

17. Types of tectonic activity
Converging – subduction zones (Chile coast) Himalayas
Spreading – mid-Atlantic rift
Sliding – St. Andreas fault
Figure The Mid-Atlantic Ridge
This artist’s rendition shows the Mid-Atlantic
Ridge, an immense mountain ridge that rises up from the floor of the
North Atlantic Ocean. It is caused by lava seeping up from the Earth’s
interior along a rift that extends from Iceland to Antarctica. (Courtesy of
M. Tharp and B. C. Heezen)

18. All plate boundaries are sources of volcanism and earthquakes
Figure The Earth’s Major Plates
The boundaries of the Earth’s major plates are the scenes of violent seismic and geologic
activity. Most earthquakes occur where plates separate, collide, or rub
together. Plate boundaries are therefore easily identified simply by
plotting earthquake epicenters (shown here as dots) on a map. The colors
of the dots indicate the depths at which the earthquakes originate. (Data
from Harvard CMT catalog; plot by M. Boettcher and T. Jordan.)
Show Science Bulletins “Earthquakes today”:

19. Constructive and destructive plate boundaries
Figure The Mechanism of Plate Tectonics
Convection currents in the asthenosphere, the soft upper layer of the mantle, are
responsible for pushing around rigid, low-density crustal plates. New crust
forms in oceanic rifts, where lava oozes upward between separating
plates. Mountain ranges and deep oceanic trenches are formed where
plates collide.
Figure The Mid-Atlantic Ridge (insert)
This artist’s rendition shows the Mid-Atlantic
Ridge, an immense mountain ridge that rises up from the floor of the
North Atlantic Ocean. It is caused by lava seeping up from the Earth’s
interior along a rift that extends from Iceland to Antarctica. (Courtesy of
M. Tharp and B. C. Heezen)

20. Figure 9-17 The Separation of Two Plates
The plates that carry Africa and Arabia are moving apart, leaving a great rift that has been
flooded to form the Red Sea. This view from orbit shows the northern Red Sea,
which splits into the Gulf of Suez and the Gulf of Aqaba. (Gemini 12, NASA)

21. Figure 9-18 The Collision of Two Plates
The plates that carry India and
China are colliding. Instead of one plate being subducted
beneath the other, both plates are pushed upward, forming the
Himalayas. Mount Everest is one of the snow-covered peaks near the
center of this photograph taken from orbit. (Apollo 7, NASA)

22. The St. Andreas Fault – a type of conservative plate boundary

23. A few “rock” terms
Chemical elements make minerals (single atom or compounds)
Single atom: diamond, gold nugget.
Compound: feldspar=K,Al,Si,O; quartz=Si,O)
One or more minerals make rocks
Rock: granite = feldspar + quartz
Feldspar
Quartz
Granite
Figure 9-19 Igneous, Sedimentary, and Metamorphic Rocks
(a) Igneous rocks such as basalt are created when molten materials solidify. This example
contains iron-rich minerals that give it its dark color. (b) Sedimentary
rocks such as sandstone are typically formed when loose particles of soil
or sand are fused into rock by the presence of other minerals, which act
as a cement. (c) Metamorphic rocks are produced when igneous or
sedimentary rocks are subjected to high temperatures and pressures
deep within the Earth’s crust. Marble (left) is formed from sedimentary
limestone; schist (right) is formed from igneous rock. (W. J. Kaufmann III;
specimens courtesy Mineral Museum, California Division of Mines)

24. Plate tectonics and the variety of rocks
An example: In the early Earth CO2 was outgassed from volcanos. As it dissolved in the oceans it formed carbonate minerals. One such mineral, calcite became part of sedimentary rocks such as limestone, which were later subducted, mixed up resulting in, e.g., marble is a metamorphic rock.
Figure 9-19 Igneous, Sedimentary, and Metamorphic Rocks
(a) Igneous rocks such as basalt are created when molten materials solidify. This example
contains iron-rich minerals that give it its dark color. (b) Sedimentary
rocks such as sandstone are typically formed when loose particles of soil
or sand are fused into rock by the presence of other minerals, which act
as a cement. (c) Metamorphic rocks are produced when igneous or
sedimentary rocks are subjected to high temperatures and pressures
deep within the Earth’s crust. Marble (left) is formed from sedimentary
limestone; schist (right) is formed from igneous rock. (W. J. Kaufmann III;
specimens courtesy Mineral Museum, California Division of Mines)

25. Earth’s early atmosphere
Early atmosphere: H, He, C, O, …. Same mix as the solar nebula
H, He easily escape, some H forms H2O which remains
Early atmosphere very dense and filled with water vapour
Earth cools, vapour becomes liquid, forms oceans
Earth would be very cold at this point, but CO2 outgassed from volcanoes is a green-house gas and keeps Earth warmer than it would be otherwise.
CO2 is a green-house gas: in the atmosphere to keep the Earth warm
Some CO2 dissolves in water and goes in the oceans where it is locked in rocks – some CO2 remains in the atmosphere
When we release too much CO2 in the atmosphere we increase the green-house effect and … the end of the story when we talk more about the roasting surface of Venus!

26. The rise of Oxygen and complex life
Photosynthesis + Respiration: regulation of O2
Figure The Increase in Atmospheric Oxygen
This graph shows how the amount of oxygen in the atmosphere (expressed as a percentage of its
present-day value) has evolved with time. Note that the atmosphere
contained essentially no oxygen until about 2 billion years ago. (Adapted
from Preston Cloud, “The Biosphere,” Scientific American, September 1983, p. 176)

27. Q40. This photograph shows the soil at Daspoort
Tunnel near Pretoria, South Africa. The whitish layer that extends
from lower left to upper right is 2.2 billion years old.
Its color is due to a lack of iron oxide. More recent soils typically
contain iron oxide and have a darker color. Explain
what this tells us about the history of the Earth’s atmosphere.
A40. The facts stated in the question tell us that the Earth’s atmosphere did not contain oxygen in much abundance 2.2 billion years ago when the whitish layer formed. The high oxygen content in the more recent darker material formed when there was more oxygen and so is oxygen rich.

28. Life on Earth Humans (~100,000 yr ago)
Cambrian explosion (~500 Myr ago)
Protoplanetary disk(~4.5 Gyr ago)
First life (~3.8 Gyr ago)

29. The rise of oxygen Science Bulletin’s piece

30. Comparing Earth’s, Venus’ and Mars’ atmospheres
Read the Book’s 9.5: comparison atmospheres to understand the importance of and the reason for the differences in this table.

31. Pressure decreases with altitude. Temperature is more complicated …
At hundreds of degrees, why is the Shuttle not burning up?
50% of the atmosphere is in the troposphere.
Figure Temperature Profile of the Earth’s Atmosphere
This graph shows how the temperature in the Earth’s atmosphere varies with altitude. In
the troposphere and mesosphere, temperature decreases with increasing
altitude; in the stratosphere and thermosphere, temperature actually
increases with increasing altitude.
Airheated by land rises in the troposphere expanding as it goes up, expending energy and cooling.

32. Figure 9-24 Circulation Patterns in the Earth’s Atmosphere
The dominant circulation in our atmosphere consists of six convection cells, three
in the northern hemisphere and three in the southern hemisphere.
In the northern temperate region (including the continental United
States), the prevailing winds at the surface are from the southwest
toward the northeast. Farther south, within the northern tropical
region (for example, Hawaii), the prevailing surface winds are from
northeast to southwest.

33. The Earth biosphere Figure 9-25 The Earth’s Biosphere
This image, based on data from the
SeaWIFS spacecraft, shows the distribution of plant life over
the Earth’s surface. The ocean colors show where free-floating
microscopic plants called phytoplankton are found. (NASA Visible Earth)

34. The Earth biosphere
Climate can vary by natural causes (uneven Sun’s radiation, Earth’s axis precession …).
CO2 levels can also vary naturally (intense periods of volcanic activity: extinction 250 million years ago driven by volcanoes in Siberia ….).
However, human influence ha been far above these natural chances (deforestation, destruction of the ozone layer, increase in CO2 emission).

35. Figure 9-26 The Human Population
Data and estimates from the U.S. Bureau of the
Census, the Population Reference Bureau, and the United Nations
Population Fund were combined to produce this graph showing the
human population from 500 B.C. to 2000 A.D. The population began to rise
in the eighteenth century and has been increasing at an astonishing rate
since 1900.

36. Figure 9-27 The Deforestation of Amazonia
The Amazon, the world’s largest rain
forest, is being destroyed at a rate of 20,000 square kilometers per year
in order to provide land for grazing and farming and as a source for
lumber. About 80% of the logging is being carried out illegally. (Martin
Wendler/Okapia/Photo Researchers)

37. 90% of Ozone is between 40 and 60 km above ground.
Ozone is O3. It is broken down by UV light so it absorbs UV light and protects us from it. It is then made by a reaction of O2 an O. It is also destroyed by reacting with O, a reaction that is catalysed by other chemicals such as CFCs
Figure The Antarctic Ozone Hole
These two false-color
images show that there was a net
decrease of 50% in stratospheric ozone
over Antarctica between October 1979
and September The amount of
ozone at midlatitudes, where most of
the human population lives, decreased
by 10 to 20% over the same period.
(GSFC/NASA)

38. Figure 9-29 Atmospheric Carbon Dioxide Is Increasing
This graph shows measurements of atmospheric carbon dioxide in parts per million (ppm).
The sawtooth pattern results from plants absorbing more carbon dioxide
during the spring and summer. The CO2 concentration in the atmosphere
has increased by 21% since continuous observations started in 1958.
(NOAA/Scripps Institution of Oceanography)

39. Figure 9-30 Atmospheric CO2 and Changes in Global Temperature
This figure shows how the
carbon dioxide concentration in our atmosphere (upper
curve) and the Earth’s average surface temperature (lower
curve) have changed since 1000 A.D. The increase in CO2
since 1800 due to burning fossil fuels has strengthened
the greenhouse effect and caused a dramatic
temperature increase. (Intergovernmental Panel on Climate
Change and Hadley Centre for Climate Prediction and
Research, U.K. Meteorological Office)

40. An Inconvenient Truth, by Al Gore http://video. google. com/videoplay
Figure 9-31 A Melting Antarctic Ice Shelf
Global warming caused the Larsen B ice shelf to break up in early This ice shelf,
which was about the size of Rhode Island, is thought to have been part of
the Antarctic coast for the past 12,000 years. (NASA/GSFC/LaRC/JPL, MIST
Team)

41. Observations of the Moon
Aristotle thought that the lunar imperfections were actually changes in density and the Moon was a perfect orb.
Plutarch ( AD) suggested that it was due to canyons and valleys and might be inhabited.
It was Galileo that finally put the matter to rest using a telescope.
Influence of the Moon on human life.

42. The Moon Note the Sun The space suite Lunar surface is old
Apollo 16, April
Note the Sun
The space suite

43. One small step for (a) man, one giant leap for mankind
Must watch the great Aussie movies “The Dish”.

44. Key Ideas
The Earth’s Energy Sources: All activity in the Earth’s atmosphere, oceans, and surface is powered by three sources of energy.
Solar energy is the energy source for the atmosphere. In the greenhouse effect, some of this energy is trapped by infrared absorbing gases in the atmosphere, raising the Earth’s surface temperature.
Tidal forces from the Moon and Sun help to power the motion of the oceans.
The internal heat of the Earth is the energy source for geologic activity.

45. Key Ideas
The Earth’s Interior: Studies of seismic waves (vibrations produced by earthquakes) show that the Earth has a small, solid inner core surrounded by a liquid outer core. The outer core is surrounded by the dense mantle, which in turn is surrounded by the thin low-density crust.
Seismologists deduce the Earth’s interior structure by studying how longitudinal P waves and transverse S waves travel through the Earth’s interior.
The Earth’s inner and outer cores are composed of almost pure iron with some nickel mixed in. The mantle is composed of iron rich minerals.
Both temperature and pressure steadily increase with depth inside the Earth.

46. Key Ideas
Plate Tectonics: The Earth’s crust and a small part of its upper mantle form a rigid layer called the lithosphere. The lithosphere is divided into huge plates that move about over the plastic layer called the asthenosphere in the upper mantle.
Plate tectonics, or movement of the plates, is driven by convection within the asthenosphere. Molten material wells up at oceanic rifts, producing seafloor spreading, and is returned to the asthenosphere in subduction zones. As one end of a plate is subducted back into the asthenosphere, it helps to pull the rest of the plate along.

47. Key Ideas
Plate tectonics is responsible for most of the major features of the Earth’s surface, including mountain ranges, volcanoes, and the shapes of the continents and oceans.
Plate tectonics is involved in the formation of the three major categories of rocks: igneous rocks (cooled from molten material), sedimentary rocks (formed by the action of wind, water, and ice), and metamorphic rocks (altered in the solid state by extreme heat and pressure).

48. Key Ideas
The Earth’s Magnetic Field and Magnetosphere: Electric currents in the liquid outer core generate a magnetic field. This magnetic field produces a magnetosphere that surrounds the Earth and blocks the solar wind from hitting the atmosphere.
A bow-shaped shock wave, where the supersonic solar wind is abruptly slowed to subsonic speeds, marks the outer boundary of the magnetosphere.
Most of the particles of the solar wind are deflected around the Earth by the magnetosphere.
Some charged particles from the solar wind are trapped in two huge, doughnut-shaped rings called the Van Allen belts. An excess of these particles can initiate an auroral display.

49. Key Ideas
The Earth’s Atmosphere: The Earth’s atmosphere differs from those of the other terrestrial planets in its chemical composition, circulation pattern, and temperature profile.
The Earth’s atmosphere evolved from being mostly water vapor to being rich in carbon dioxide. A strong greenhouse effect kept the Earth warm enough for water to remain liquid and to permit the evolution of life.

50. Key Ideas
The appearance of photosynthetic living organisms led to our present atmospheric composition, about four-fifths nitrogen and one-fifth oxygen.
The Earth’s atmosphere is divided into layers called the troposphere, stratosphere, mesosphere, and thermosphere. Ozone molecules in the stratosphere absorb ultraviolet light.
Because of the Earth’s rapid rotation, the circulation in its atmosphere is complex, with three circulation cells in each hemisphere.

51. Key Ideas
The Biosphere: Human activity is changing the Earth’s biosphere, on which all living organisms depend.
Industrial chemicals released into the atmosphere have damaged the ozone layer in the stratosphere.
Deforestation and the burning of fossil fuels are increasing the greenhouse effect in our atmosphere and warming the planet. This can lead to destructive changes in the climate.

52. Which of the following has the smallest effect on the motions of the Earth's atmosphere and oceans?
solar energy
the Earth’s internal heat
tidal forces
both B and C
This is a misleading question. All of these have comparably large effects on the atmosphere and oceans.
Q9.1

53. Which of the following has the smallest effect on the motions of the Earth's atmosphere and oceans?
solar energy
the Earth’s internal heat
tidal forces
both B and C.
This is a misleading question. All of these have comparably large effects on the atmosphere and oceans.
A9.1

54. What energy source creates clouds in our atmosphere?
The Sun
Earth’s internal heat
Tidal interactions with the Moon
The solar wind
None of the above
Q9.2

55. What energy source creates clouds in our atmosphere?
The Sun
Earth’s internal heat
Tidal interactions with the Moon
The solar wind
None of the above
A9.2

56. What energy source leads to mountain building on Earth?
The Sun
Earth’s internal heat
Tidal interactions with the Moon
The solar wind
None of the above
Q9.3

57. What energy source leads to mountain building on Earth?
The Sun
Earth’s internal heat
Tidal interactions with the Moon
The solar wind
None of the above
A9.3

58. In the greenhouse effect,
some infrared radiation emitted by the Earth’s surface is absorbed by the atmosphere.
some ultraviolet radiation emitted by the Earth’s surface is absorbed by the atmosphere.
vegetation traps thermal energy near the surface.
infrared radiation from the Sun is captured as it enters the Earth’s atmosphere.
infrared radiation from the Sun is reflected by the Earth’s atmosphere into space.
Q9.4

59. In the greenhouse effect,
some infrared radiation emitted by the Earth’s surface is absorbed by the atmosphere.
some ultraviolet radiation emitted by the Earth’s surface is absorbed by the atmosphere.
vegetation traps thermal energy near the surface.
infrared radiation from the Sun is captured as it enters the Earth’s atmosphere.
infrared radiation from the Sun is reflected by the Earth’s atmosphere into space.
A9.4

60. Which of the follow best describes the natural greenhouse effect (not including human influence) on Earth?
There is no natural greenhouse effect.
The natural greenhouse effect keeps Earth’s average temperature relatively constant and above freezing.
The natural greenhouse effect has continuously increased the average temperature of the atmosphere and surface over the past 4.56 billion years.
The natural greenhouse effect has continuously decreased the average temperature of the atmosphere and surface over the past 4.56 billion years.
Q9.5

61. Which of the follow best describes the natural greenhouse effect (not including human influence) on Earth?
There is no natural greenhouse effect.
The natural greenhouse effect keeps Earth’s average temperature relatively constant and above freezing.
The natural greenhouse effect has continuously increased the average temperature of the atmosphere and surface over the past 4.56 billion years.
The natural greenhouse effect has continuously decreased the average temperature of the atmosphere and surface over the past 4.56 billion years.
A9.5

62. Which of the following is not an important greenhouse gas?
Carbon dioxide
Methane
Water
Ammonia
All of these are important greenhouse gases.
Q9.6

63. Which of the following is not an important greenhouse gas?
Carbon dioxide
Methane
Water
Ammonia
All of these are important greenhouse gases.
A9.6

64. Which of the following is a correct statement about seismic waves used to map the Earth’s interior structure?
P waves are longitudinal and are able to travel through solids and liquids; S waves are transverse and can only travel through liquids.
P waves are transverse and are able to travel through solids and liquids; S waves are longitudinal and can only travel through liquids.
P waves are transverse and are able to travel through solids and liquids; S waves are longitudinal and can only travel through solids.
P waves are longitudinal and are able to travel through solids and liquids; S waves are transverse and can only travel through solids.
Q9.7

65. Which of the following is a correct statement about seismic waves used to map the Earth’s interior structure?
P waves are longitudinal and are able to travel through solids and liquids; S waves are transverse and can only travel through liquids.
P waves are transverse and are able to travel through solids and liquids; S waves are longitudinal and can only travel through liquids.
P waves are transverse and are able to travel through solids and liquids; S waves are longitudinal and can only travel through solids.
P waves are longitudinal and are able to travel through solids and liquids; S waves are transverse and can only travel through solids.
A9.7

66. The Earth’s magnetic field is generated by
electric currents in the liquid outer core; the field has never changed direction.
electric currents in the liquid inner core; the field has never changed direction.
electric currents in the liquid outer core; the field has reversed many times in the past.
electric currents in the liquid inner core; the field has reversed many times in the past.
electric currents caused by interactions with the solar wind.
Q9.8

67. The Earth’s magnetic field is generated by
electric currents in the liquid outer core; the field has never changed direction.
electric currents in the liquid inner core; the field has never changed direction.
electric currents in the liquid outer core; the field has reversed many times in the past.
electric currents in the liquid inner core; the field has reversed many times in the past.
electric currents caused by interactions with the solar wind.
A9.8

68. The Red Sea rift is
formed by two tectonic plates moving apart.
a subduction zone, where one plate is pushed under the other.
a fold in the middle of a plate caused by compressing forces on both sides of the plate.
a hot spot in Earth’s mantle, which is spreading two plates apart.
the result of a earthquake that occurred thousands of years ago.
Q9.9

69. The Red Sea rift is
formed by two tectonic plates moving apart.
a subduction zone, where one plate is pushed under the other.
a fold in the middle of a plate caused by compressing forces on both sides of the plate.
a hot spot in Earth’s mantle, which is spreading two plates apart.
the result of a earthquake that occurred thousands of years ago.
A9.9

70. The Mid-Atlantic Ridge is best described as
a line of undersea mountains caused by two plates colliding and pushing each other upward.
a fold in the middle of a plate caused by compressing forces on both sides of the plate.
a region where one plate is being subducted beneath another.
a site where two plates are moving apart, allowing molten subsurface rock to rise upward.
a region in the middle of a plate that happens to lie over a hot spot in the mantle.
Q9.10

71. The Mid-Atlantic Ridge is best described as
a line of undersea mountains caused by two plates colliding and pushing each other upward.
a fold in the middle of a plate caused by compressing forces on both sides of the plate.
a region where one plate is being subducted beneath another.
a site where two plates are moving apart, allowing molten subsurface rock to rise upward.
a region in the middle of a plate that happens to lie over a hot spot in the mantle.
A9.10

72. The Earth shows very little evidence of meteor impacts because
plate tectonics is continuously recycling the Earth’s crust.
wind and rain have continually eroded the Earth’s surface.
very few meteors struck the Earth in the past.
vegetation has covered the craters.
Both A and B are correct.
Q9.11

73. The Earth shows very little evidence of meteor impacts because
plate tectonics is continuously recycling the Earth’s crust.
wind and rain have continually eroded the Earth’s surface.
very few meteors struck the Earth in the past.
vegetation has covered the craters.
Both A and B are correct.
A9.11

74. If the early atmosphere of the Earth was composed of carbon dioxide, why does the present atmosphere contain oxygen molecules?
Volcanoes slowly enriched the Earth’s atmosphere with oxygen.
When life first developed on the Earth, this life produced oxygen from carbon dioxide by photosynthesis.
Rainwater slowly broke down carbon dioxide into its components.
Oxygen was captured from space over many millions of years.
Solar radiation breaks down CO2.
Q9.12

75. If the early atmosphere of the Earth was composed of carbon dioxide, why does the present atmosphere contain oxygen molecules?
Volcanoes slowly enriched the Earth’s atmosphere with oxygen.
When life first developed on the Earth, this life produced oxygen from carbon dioxide by photosynthesis.
Rainwater slowly broke down carbon dioxide into its components.
Oxygen was captured from space over many millions of years.
Solar radiation breaks down CO2.
A9.12

76. Ozone is a molecule made up of three oxygen atoms
Ozone is a molecule made up of three oxygen atoms. The ozone layer that protects the Earth’s surface from ultraviolet light
has been present and stable for as long as we have been measuring it.
has shown gradual changes over the last 20 years with a hole appearing over Antarctica.
shows no holes yet but appears to be getting thinner.
shows rather large seasonal changes with large holes appearing over the North and South Poles during their respective winters.
is no longer present.
Q9.13

77. Ozone is a molecule made up of three oxygen atoms
Ozone is a molecule made up of three oxygen atoms. The ozone layer that protects the Earth’s surface from ultraviolet light
has been present and stable for as long as we have been measuring it.
has shown gradual changes over the last 20 years with a hole appearing over Antarctica.
shows no holes yet but appears to be getting thinner.
shows rather large seasonal changes with large holes appearing over the North and South Poles during their respective winters.
is no longer present.
A9.13

78. The oxygen in our atmosphere is chemically reactive, combining with other elements to form compounds, and is also being used by respiratory life. Despite this, the amount of oxygen in our atmosphere is not decreasing because it is being replenished by
outgassing from seawater.
volcanic eruptions.
biological activity, such as photosynthesis.
meteors and comets, which bring oxygen to the Earth.
solar radiation breaking down CO2.
Q9.14

79. The oxygen in our atmosphere is chemically reactive, combining with other elements to form compounds, and is also being used by respiratory life. Despite this, the amount of oxygen in our atmosphere is not decreasing because it is being replenished by
outgassing from seawater.
volcanic eruptions.
biological activity, such as photosynthesis.
meteors and comets, which bring oxygen to the Earth.
solar radiation breaking down CO2.
A9.14