Reading Passage 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.

Paleontologists 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.

“Nothing is sure but death and taxes, and of course that north is north GMAT Reading Comprehension”- is a reading comprehension exercise for the GMAT. Candidates must be extremely skilled in GMAT reading comprehension. This GMAT reading comprehension section contains 4 comprehension questions. The GMAT Reading Comprehension questions are designed to assess candidates' ability to comprehend, analyzation, and application skills. GMAT Reading Comprehension Practice Questions can help candidates who are actively preparing.

Solutions and Explanation

1. The main purpose of the passage is to

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

2. “Magnetic reversal” refers to

1. the atoms in rock crystals pointing toward the magnetic north pole.
2. north becoming south and south becoming north.
3. the reversal of direction in ancient lava flows.
4. a reversal of the direction of convection currents in the outer core of the earth.
5. 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?

1. solidification of rocks formed from magmas
2. the extinction of certain species 700,000 years ago
3. the rapid change from “normal” to “reversed” polarity
4. the change in the direction of convection currents in the earth’s outer core
5. lava flows “pointing” to magnetic north

4. It is reasonable to infer from the passage that

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

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