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In the mid-1970’s, Walter Alvarez, a geologist, was studying
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17 Jan 2020, 19:48
17 Jan 2020, 19:48
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In the mid-1970’s, Walter Alvarez, a geologist, was studying Earth’s polarity. It had recently been learned that the orientation of the planet’s magnetic field reverses, so that every so often, in effect, south becomes north and vice versa. Alvarez and some colleagues had found that a certain formation of pinkish limestone in Italy, known as the scaglia rossa, recorded these occasional reversals. The limestone also contained the fossilized remains of millions of tiny sea creatures called foraminifera. Alvarez became interested in a thin layer of clay in the limestone that seemed to have been laid down around the end of the Cretaceous Period. Below the layer, certain species of foraminifera—or forams, for short—were preserved. In the clay layer, there were no forams. Above the layer, the earlier species disappeared and new forams appeared. Having been taught the uniformitarian view, which held that any apparent extinctions throughout geological time resulted from ‘the incompleteness of the fossil record’ rather than an actual extinction, Alvarez was not sure what to make of the lacuna in geological time corresponding to the missing foraminifera, because the change looked very abrupt.
Had Walter Alvarez not asked his father, the Nobel Prize-winning physicist Luis Alvarez, how long the clay had taken to deposit, the younger Alvarez may not have thought to use iridium, an element rarely found on earth but more plentiful in meteorites, to answer this question. Iridium, in the form of microscopic grains of cosmic dust, is constantly raining down on the planet. The Alvarezes reasoned that if the clay layer had taken a significant amount of time to deposit, it would contain detectable levels of iridium. The results were startling: far too much iridium had shown up. The Alvarez hypothesis, as it became known, was that everything—not just the clay layer—could be explained by a single event: a six-mile-wide asteroid had slammed into Earth, killing off not only the forams but also the dinosaurs and all the other organisms that went extinct at the end of the Cretaceous period.
Had Walter Alvarez not asked his father, the Nobel Prize-winning physicist Luis Alvarez, how long the clay had taken to deposit, the younger Alvarez may not have thought to use iridium, an element rarely found on earth but more plentiful in meteorites, to answer this question. Iridium, in the form of microscopic grains of cosmic dust, is constantly raining down on the planet. The Alvarezes reasoned that if the clay layer had taken a significant amount of time to deposit, it would contain detectable levels of iridium. The results were startling: far too much iridium had shown up. The Alvarez hypothesis, as it became known, was that everything—not just the clay layer—could be explained by a single event: a six-mile-wide asteroid had slammed into Earth, killing off not only the forams but also the dinosaurs and all the other organisms that went extinct at the end of the Cretaceous period.
1. It can be inferred from the passage that had the scaglia rossa not exhibited a certain geological property then which of the following would most likely have been true?
(A) Walter Alvarez would not have used the distribution of foraminifera in limestone as the basis for a conjecture.
(B) Scientists would have been unable to determine a shift in the Earth’s magnetic fields.
(C) The rocks would not have been of any immediate utility to scientists.
(D) Iridium still would have been used to substantiate a hypothesis regarding the extinction of dinosaurs.
(E) The gap in foraminifera fossil record would have served an immediate purpose.
2. Proponents of the uniformitarian view would most likely argue that
(A) the clay layer actually contained foram too small for Alvarez to detect.
(B) the absence of foram suggested a mass extinction
(C) iridium could likely be found in the clay layer
(D) that the lack of forams in the clay reflected a gap in the fossil record
(E) the orientation of the earth’s magnetic field is capable of reversing
3. According to the passage, it can most likely be inferred that iridium
(A) can be used by scientists to determine the duration of an event
(B) causes mass extinctions in a short period
(C) gathers excessively in clay deposits
(D) helps scientists determine the orientation of the magnetic field
(E) leads to inaccurate conclusions regarding the chronology of an event
4. The Alvarezes concluded that a meteorite was responsible for a mass extinction because
(A) dinosaurs were prone to the effects of iridium
(B) it could account for the heightened presence of an element
(C) cosmic dust in the form of iridium constantly makes its way to the Earth’s surface
(D) the scaglia rossa had a sudden gap in traceable iridium
(E) the scientific community was unable to provide a more valid hypothesis
(A) Walter Alvarez would not have used the distribution of foraminifera in limestone as the basis for a conjecture.
(B) Scientists would have been unable to determine a shift in the Earth’s magnetic fields.
(C) The rocks would not have been of any immediate utility to scientists.
(D) Iridium still would have been used to substantiate a hypothesis regarding the extinction of dinosaurs.
(E) The gap in foraminifera fossil record would have served an immediate purpose.
Show: ::
A
2. Proponents of the uniformitarian view would most likely argue that
(A) the clay layer actually contained foram too small for Alvarez to detect.
(B) the absence of foram suggested a mass extinction
(C) iridium could likely be found in the clay layer
(D) that the lack of forams in the clay reflected a gap in the fossil record
(E) the orientation of the earth’s magnetic field is capable of reversing
Show: ::
D
3. According to the passage, it can most likely be inferred that iridium
(A) can be used by scientists to determine the duration of an event
(B) causes mass extinctions in a short period
(C) gathers excessively in clay deposits
(D) helps scientists determine the orientation of the magnetic field
(E) leads to inaccurate conclusions regarding the chronology of an event
Show: ::
A
4. The Alvarezes concluded that a meteorite was responsible for a mass extinction because
(A) dinosaurs were prone to the effects of iridium
(B) it could account for the heightened presence of an element
(C) cosmic dust in the form of iridium constantly makes its way to the Earth’s surface
(D) the scaglia rossa had a sudden gap in traceable iridium
(E) the scientific community was unable to provide a more valid hypothesis
Show: ::
B
Re: In the mid-1970’s, Walter Alvarez, a geologist, was studying
[#permalink]
30 Jun 2020, 05:01
30 Jun 2020, 05:01
1
In the passage says:
Then mentioned:
So the answer for question 1 is A.
Quote:
In the mid-1970’s, Walter Alvarez, a geologist, was studying Earth’s polarity. It had recently been learned that the orientation of the planet’s magnetic field reverses, so that every so often, in effect, south becomes north and vice versa. Alvarez and some colleagues had found that a certain formation of pinkish limestone in Italy, known as the scaglia rossa, recorded these occasional reversals.
Then mentioned:
Quote:
Alvarez was not sure what to make of the lacuna in geological time corresponding to the missing foraminifera, because the change looked very abrupt.
So the answer for question 1 is A.
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Re: In the mid-1970s, Walter Alvarez, a geologist, was studying
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21 Jun 2022, 10:11
21 Jun 2022, 10:11
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