Hi everyone,
Took 14:40 minutes and got 5/6 correct.
------------------------------------------------------------------------------------------P1Paragraph one starts with presenting the subject at hand: the magnetic field and polarity.
We know that when conditions are normal the compass will point at north.
On the other hand, when the polarity is reversed the compass will point at south.
We are also given that this changes in polarity has been occurring at an increasing rate and that are not instantaneous.
Brief summary: Polarity changes occur more and more but not instantaneous
P2Paragraph 2 stresses the fact that the causes behind the change in polarity are not very well understood.
What we know is that the magnetic field is produced by the motion of free electrons in the outer core (outer core= zone between the mantle and its inner core).
What on the other hand we don't understand well is the role of heart's gravity and rotation, role that affects the temperature and the density of the fluids in the outer core.
The heat-fluid pattern of the outer core in fact might affect the magnetic field
Brief summary: The magnetic field and causes behind the changes
P3Paragraph 3 gives us 2 of the many explanation to this phenomenon.
The first one is the heat transfer hypothesis, according to which there is a creation of blobs (cold or warm) that affect the heat-fluid patterns of the outer core, impacting on the polarity change.
The second,
controversial, explanation is the asteroid impact one.
According to this theory an asteroid has an impact, its dust reaches the atmosphere, provoking the drop of the temperatures and consequently the increase of the ice caps. Such increase affects the rotational acceleration of the mantle, causing friction and possibly generating a change in polarity.
Brief summary: Two explanation the the phenomenon
P4Paragraph 4 evaluates the two theories in terms of accountability for the long term frequency increase.
The asteroid impact theory at first seems plausible because the temperature drop in the ocean would allow impacts from smaller asteroid to induce the ice caps growth and vice versa.
However the first theory is more credible since it relies solely on events which are earth based
Brief summary: accountability of the 2 theories
Main pointThe main point is to investigate the causes behind the shift in polarity
------------------------------------------------------------------------------------------1.Which one of the following statements regarding the Earth’s outer core is best supported by information presented in the passage?
Pre-thinking
Inference question
The earth outer core is described in P2. Outer core= area between the mantle and its inner core
(A) Heat circulation in the outer core controls the growth and diminution of the
polar ice caps.ice caps are nominated in P3 but are out of context here(B) Impact of asteroids on the Earth’s surface alters the way in which the outer
core vents its heat into the mantle.the impact causes friction in the mantle(C) Motion of electrons within the metallic fluid in the outer core produces the Earth’s magnetic field.
This statement seems more like a paraphrase of the information in P2(D) Friction and turbulence near the boundary between the outer core and the mantle are
typically caused by asteroid impacts.
the asteroid impact is a theory not a proven fact(E) Cessation of heat circulation within the outer core brings on multiple reversals in the Earth’s magnetic field.
cannot be inferred------------------------------------------------------------------------------------------2.The author’s objection to the second hypothesis discussed in the passage is most applicable to which one of the following explanations concerning the extinction of the dinosaurs?
Pre-thinking
Application question
The asteroid impact theory is rejected because it provides an explanation based on something that comes from space. So, what we are looking for is an explanation for the extinction of dinosaurs based on something coming from space
(A) The extinction of the dinosaurs was the result of gradual changes in the composition of the Earth’s atmosphere that occurred over millions of years.
Not in line with pre-thinking(B) The dinosaurs became extinct when their food supply was disrupted following the emergence of mammals.
Not in line with pre-thinking(C) The dinosaurs succumbed to the new, colder environment brought about by a buildup of volcanic ash in the atmosphere.
Not in line with pre-thinking(D) After massively overpopulation the planet, dinosaurs disappeared due to widespread starvation and the rapid spread of disease.
Not in line with pre-thinking(E) After radical climatic changes resulted from the impact of a comet, dinosaurs disappeared from the Earth.
in line with pre-thinking------------------------------------------------------------------------------------------3.The author mentions the creation of blobs of different temperatures in the Earth’s outer core (Highlighted) primarily in order to
Pre-thinking
Purpose question
The purpose is to give the reason for the change in polarity.
(A) present a way in which the venting of heat from the outer core might disturb the heat-circulation pattern within the outer core
Since disturbing the heat circulation pattern equals inducing a change in the polarity, correct(B) provide proof for the proposal that ventilation of heat from the outer core into the mantle triggers polarity reversal
Provide proof might be too extreme here.(C) give an example of the way in which heat circulates between the Earth’s outer core and the Earth’s exterior
[b]Not in line with pre-thinking[/b]
(D) describe how the outer core maintains its temperature by venting its excess heat into the Earth’s mantle
Not in line with pre-thinking(E) argue in favor of the theory that heat circulation in the Earth’s interior
produces the magnetic fieldNot in line with pre-thinkingSajjadAhmad would you please explain why B is wrong?
------------------------------------------------------------------------------------------4.Which one of the following statements regarding the polarity of the Earth’s magnetic field is best supported by information in the passage?
Pre-thinking
Inference question
Let's evaluate the statements
(A) Most, but not all, geophysicists agree that the Earth’s magnetic field may exist in two distinct polarity states.
Cannot be inferred(B) Changes in the polarity of the Earth’s magnetic field have occurred more often in the recent past that in the distant past.
Can be inferred: "and that these reversals have been taking place at an increasing rate."(C) Heat transfer would cause reversals of the polarity of the Earth’s magnetic field to occur more quickly than would asteroid impact.
Cannot be inferred(D) Geophysicists’ understanding of the reversal of the Earth’s magnetic field has increased significantly since the introduction of the heat-transfer hypothesis.
Cannot be inferred(E) Friction near the boundary of the inner and outer cores brings on reversal of the polarity of the geomagnetic field.
Cannot be inferred------------------------------------------------------------------------------------------5.Which one of the following can be inferred regarding the two proposals discussed in the passage?
Pre-thinking
Inference question
I would say that the first one is more credible than the second one
(A) Since their introduction they have sharply divided the scientific community.
Cannot be inferred(B) Both were formulated in order to explain changes
in the frequency of polarity reversal.
Cannot be inferred(C) Although no firm conclusions regarding them have yet been reached,
both have been extensively investigated.Cannot be inferred(D) They are not the only proposals scientists have put forward to explain the phenomenon of polarity reversal.
"Several explanations for this phenomenon have been proposed."(E)
Both were introduced some time ago and have since fallen into disfavor among geophysicists.Cannot be inferred------------------------------------------------------------------------------------------6.The author mentions each of the following as possible contributing causes to reversals of the Earth’s magnetic field EXCEPT
Pre-thinking
Detail question
Let's evaluate the statements
(A) changes in the way heat circulates within the outer core fluid
"The reversal phenomenon may be triggered when something disturbs the heat circulation pattern of the outer core fluid, and with it the magnetic field."
(B) extended periods of colder temperatures on the Earth’s surface
"In this scenario an extended period of cold and darkness results from the impact of an asteroid large enough to send a great cloud of dust into the atmosphere."
(C) the creation of circulation blobs of outer core material of different temperatures
"For example, such heat transfer could create hotter (rising) or cooler (descending) blobs of material from the inner and outer boundaries of the fluid core, thereby perturbing the main heat-circulation pattern."
(D) changes in circulation patterns in the Earth’s oceans
Not mentioned(E) clouding of the Earth’s atmosphere by a large amount of dust
"In this scenario an extended period of cold and darkness results from the impact of an asteroid large enough to send a great cloud of dust into the atmosphere. "------------------------------------------------------------------------------------------It is a good day to be alive!