Nothing is sure but death and taxes, and of course that north is north

Question

Nothing is sure but death and taxes, and of course that north is north and south is south, and thus it has always been, so they say. But they’d be wrong. You can perhaps be sure about death and taxes, but you might want to reconsider the rest of it. In fact, at many times in our planet’s history, north has become south and south has become north, in a process called magnetic reversal.

Paleogeologists have discovered the existence of these mysterious phenomena (in a field of study known as paleomagnetism) by investigating rocks. When rocks are being formed from magmas, atoms within their crystals respond to the earth’s magnetic field by “pointing” toward the magnetic north pole. By age dating the rocks and noting their magnetic alignment, scientists can determine where on earth the north pole was located at that time because as the rocks solidified, they trapped that information within them. The study of ancient lava flows has revealed that at certain periods in the earth’s history magnetic north was directly opposite its present location. In fact, it has been determined that the north/south reversal has occurred on average every 500,000 years and that the last reversal took place about 700,000 years ago. Scientists call those periods of “normal” polarity (the magnetic orientation of our modern era) and “reversed” polarity (the magnetic orientation of the reverse situation) by the name “magnetic chrons.”

Although the fact of such reversals is clear, why and how they happen and their effects on the planet are subjects of considerable debate. Because no one knows precisely how the earth’s magnetic field is produced, it becomes difficult to say how it might be reversed. Among explanations proposed are a reversal of the direction of convection currents in the liquid outer core of the earth and a collision between the earth and a meteorite or comet. And while the precise effects of a reversal are not known, there can be little doubt that the earth would receive during the process a great deal more damaging ultraviolet radiation than it now does and that such occurrences have been correlated with the extinction of certain species in the geologic past.    1 
 1. The main purpose of the passage is to

A. explain what is meant by “normal” polarity and its relationship to “magnetic chrons.”
B. present opposing hypotheses concerning the earth’s magnetic field and argue that one of them is adequate.
C. explain the process of magnetic reversal and how it was discovered.
D. discuss the difference between “normal” and “reversed” polarities and how the difference affects convection currents in the earth’s outer core.
E. set forth a time table for magnetic reversal.

2 
 2. “Magnetic reversal” refers to

A. the atoms in rock crystals pointing toward the magnetic north pole.
B. north becoming south and south becoming north.
C. the reversal of direction in ancient lava flows.
D. a reversal of the direction of convection currents in the outer core of the earth.
E. a disturbance in the regular 500,000 year cycle of the magnetic field.

3 
 3. According to the passage, which of the following was crucial to the discovery of magnetic reversal?

A. solidification of rocks formed from magmas
B. the extinction of certain species 700,000 years ago
C. the rapid change from “normal” to “reversed” polarity
D. the change in the direction of convection currents in the earth’s outer core
E. lava flows “pointing” to magnetic north

4 
 4. It is reasonable to infer from the passage that

A. in spite of past reversals, “normal” polarity is now firmly established.
B. if the earth collides with a meteorite, the magnetic field will be reversed.
C. the earth’s magnetic field was produced about 700,000 years ago.
D. reversal of the direction of convection currents would signal a magnetic reversal.
E. a magnetic reversal could present a danger to humans.

RC Butler 2022  -  Practice Two RC Passages Everyday.   
Passage # 175 Date: 02-May-2022
 This question is a part of RC Butler 2022 .  Click here for Details

Source: Cliffs Test Prep.

VIGHNESHKAMATH · Answer

In my opnion, following is the answers:
1-C
2-B
3-A
4-E

wadhwakaran · Answer

Broad Idea: Magnetic Reversal

P1: You can be sure of death and taxes but not North & South because in case of Magnetic reversal it flips
P2: Investigation of the rocks revealed the phenomenon and the average time after which N becomes S and S becomes N. The current polarity is called Normal Polarity and the opposite is called Reversed Polarity.
P3: Existence of magnetic reversal is certain but effect and why it happens is not clear. One explanation has been provided for it. Also, MR is correlated to extinction of the then existing species.

1. The main purpose of the passage is to

A. explain what is meant by “normal” polarity and its relationship to “magnetic chrons.”  Only discussed in para 1, therefore, incorrect  
B. present opposing hypotheses concerning the earth’s magnetic field and argue that one of them is adequate.  No different hypotheses are present in the passage. 
C. explain the process of magnetic reversal and how it was discovered.  Discussed in P1 and P2 
D. discuss the difference between “normal” and “reversed” polarities and how the difference affects convection currents in the earth’s outer core.  first part of the option holds but the second part is incorrect 
E. set forth a time table for magnetic reversal.  no such time table has been set forth but a previous period of change in polarity has been discussed.

2. “Magnetic reversal” refers to

A. the atoms in rock crystals pointing toward the magnetic north pole.
B. north becoming south and south becoming north.  Correct simple definition 
C. the reversal of direction in ancient lava flows.
D. a reversal of the direction of convection currents in the outer core of the earth.
E. a disturbance in the regular 500,000 year cycle of the magnetic field.

3. According to the passage, which of the following was crucial to the discovery of magnetic reversal?

A. solidification of rocks formed from magmas  Yes because the solidification of magmas happened in accordance to the Earth's Magnetic Field in line with North Pole 
B. the extinction of certain species 700,000 years ago  Nope, the passage states it might be a possibility 
C. the rapid change from “normal” to “reversed” polarity  out of scope as the passage discussed about the time period after it happens. whether it is a rapid change or gradual is not mentioned 
D. the change in the direction of convection currents in the earth’s outer core  P3 says X and Y are linked to the MR, X means change in direction of convection currents and Y means the collision between meteorite and Earth 
E. lava flows “pointing” to magnetic north Incorrect

4. It is reasonable to infer from the passage that

A. in spite of past reversals, “normal” polarity is now firmly established.  Out of scope 
B. if the earth collides with a meteorite, the magnetic field will be reversed.  X and Y together signal a MR 
C. the earth’s magnetic field was produced about 700,000 years ago.  Incorrect Earth's Magnetic Field was not produced 700,000 years ago 
D. reversal of the direction of convection currents would signal a magnetic reversal.  X and Y together signal a MR 
E. a magnetic reversal could present a danger to humans.  Correct as mentioned in P3

Nothing is sure but death and taxes, and of course that north is north

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Nothing is sure but death and taxes, and of course that north is north

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