It is now generally accepted that dinosaurs (and large numbers of other animals and plants) went extinct about 65 million years ago, when Earth was hit by a giant asteroid (a rocky, planet-like celestial body). This extinction episode is called the K-T extinction, since it marks the boundary between the Cretaceous (spelled with a “K” in German) and Tertiary geologic periods. Remarkably, researchers now believe they have traced the object that caused the K-T catastrophe back to its source. If they are right, a collision in the asteroid belt nearly 100 million years before the K-T impact sealed the fate of the dinosaurs. The asteroid belt, which lies between Mars and Jupiter, is filled with millions of small and large asteroids orbiting the Sun (the largest, Ceres, is almost 600 miles across), and astronomers have recognized for some time that the belt is the major source of Earth’s meteorites (asteroids or parts of asteroids that have survived the fall to Earth’s surface). Occasional collisions, and gravitational perturbations of asteroid orbits by other solar system bodies, can send these objects hurtling toward Earth. Close similarities in mineralogical composition between asteroids and various meteorite groups confirm their connection. (The similarities are deduced using a method of spectral analysis called “reflectance spectroscopy,”which involves analysis of the light reflected from an object. Because minerals absorb light of specific, characteristic wavelengths and reflect the rest, the peaks and valleys in the spectrum of light reflected from an asteroid serve as fingerprints for the minerals present on its surface.)
In the asteroid belt, the largest rocky survivor of the collision thought to be the precursor to the K-T impact is known to astronomers as the asteroid Baptistina, which was discovered in 1890 by the French astronomer Auguste Charlois. Baptistina is about 26 miles across but it was once much larger, since it is, so to speak. the matriarch of an extended asteroid family, a large group of fragments all traveling together in roughly the same orbital path and, as far as can be determined from spectral analyses, all with a similar mineral makeup.
What is the evidence that connects the Baptistina family of asteroids to the K-T impact? It is, admittedly, circumstantial, but it is compelling. The idea was proposed in a 2007 report by a group of astronomers who used computer simulations to examine how the Baptistina asteroid family(BAF for short) had evolved over time. They began by carefully mapping out the exact locations and sizes of all known objects in the family, and then, working backward, calculated how their positions have changed through time due to the gravitational pull of other bodies, including other asteroids, the Sun, and the planets. They found that the BAF’s present-day configuration is best explained by the breakup of a single large object (at least 100 miles across) during an asteroid belt collision about 160 million years ago.
The calculations also showed that many fragments from the collision would have escaped the asteroid belt altogether, and some would have ended up in the vicinity of Earth. The researchers concluded that our planet must have experienced an increase in asteroid impacts for a period of about 100 million years after the collision. In fact, studies of the number and rate at which impact craters formed on the Moon and Earth had already shown this. The K-T collision took place during this period. While this does not prove that the impactor came from the Baptistina family, there is also another piece of corroborating evidence that bolsters the argument.
Spectral analysis of BAF asteroids indicates that they are composed of an uncommon type of extraterrestrial material that is especially rich in carbon; meteorites matching this composition are relatively rare in the world’s collections. However, sediments deposited at the K-T boundary contain a unique chemical marker that is specific to this carbon-rich meteorite family. Thus both the timing and composition fit. The conclusion that an asteroid “shower”generated by the breakup of Baptistina was the source of the K-T impactor seems highly likely; the astronomers who did the work estimated the probability at greater than 90 percent. They also concluded that around 20 percent of the large asteroids that are currently in the vicinity of Earth originate from the BAF.
1
It is now generally accepted that dinosaurs (and large numbers of other animals and plants) went extinct about 65 million years ago, when Earth was hit by a giant asteroid (a rocky, planet-like celestial body). This extinction episode is called the K-T extinction, since it marks the boundary between the Cretaceous (spelled with a “K” in German) and Tertiary geologic periods. Remarkably, researchers now believe they have traced the object that caused the K-T catastrophe back to its source. If they are right, a collision in the asteroid belt nearly 100 million years before the K-T impact sealed the fate of the dinosaurs. The asteroid belt, which lies between Mars and Jupiter, is filled with millions of small and large asteroids orbiting the Sun (the largest, Ceres, is almost 600 miles across), and astronomers have recognized for some time that the belt is the major source of Earth’s meteorites (asteroids or parts of asteroids that have survived the fall to Earth’s surface). Occasional collisions, and gravitational perturbations of asteroid orbits by other solar system bodies, can send these objects hurtling toward Earth. Close similarities in mineralogical composition between asteroids and various meteorite groups confirm their connection. (The similarities are deduced using a method of spectral analysis called “reflectance spectroscopy,”which involves analysis of the light reflected from an object. Because minerals absorb light of specific, characteristic wavelengths and reflect the rest, the peaks and valleys in the spectrum of light reflected from an asteroid serve as fingerprints for the minerals present on its surface.)
According to paragraph 1,all of the following statements about asteroids in the asteroid belt are true EXCEPT:
AThey revolve around the Sun.
BThey are all smaller than 600 miles across.
CTheir orbits can be changed by the gravitational pull of other space objects.
DThey travel closer to Earth than to other planets in their normal orbits.
2
In the asteroid belt, the largest rocky survivor of the collision thought to be the precursor to the K-T impact is known to astronomers as the asteroid Baptistina, which was discovered in 1890 by the French astronomer Auguste Charlois. Baptistina is about 26 miles across but it was once much larger, since it is, so to speak. the matriarch of an extended asteroid family, a large group of fragments all traveling together in roughly the same orbital path and, as far as can be determined from spectral analyses, all with a similar mineral makeup.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
ABaptistina was once much larger than its current 26 miles across and is the source of a large group of fragments that are similar in mineral composition and travel together.
BBaptistina is the matriarch of an asteroid family that extends for 26 miles along its orbital path.
CBaptistina travels in roughly the same orbital path as a large group of fragments whose mineral composition has been determined through the use of spectral analysis.
DBaptistina was once 26 miles long before fragments broke off from it and created an asteroid family.
3
In the asteroid belt, the largest rocky survivor of the collision thought to be the precursor to the K-T impact is known to astronomers as the asteroid Baptistina, which was discovered in 1890 by the French astronomer Auguste Charlois. Baptistina is about 26 miles across but it was once much larger, since it is, so to speak. the matriarch of an extended asteroid family, a large group of fragments all traveling together in roughly the same orbital path and, as far as can be determined from spectral analyses, all with a similar mineral makeup.
According to paragraph 2， which of the following is true of Baptistina in the asteroid belt?
AIt was named after a French astronomer.
BIt is the largest asteroid to have been identified by Auguste Charlois.
CIt is currently the largest rocky object in the asteroid belt.
DIt is the largest fragment left over from an earlier collision.
4
What is the evidence that connects the Baptistina family of asteroids to the K-T impact? It is, admittedly, circumstantial, but it is compelling. The idea was proposed in a 2007 report by a group of astronomers who used computer simulations to examine how the Baptistina asteroid family(BAF for short) had evolved over time. They began by carefully mapping out the exact locations and sizes of all known objects in the family, and then, working backward, calculated how their positions have changed through time due to the gravitational pull of other bodies, including other asteroids, the Sun, and the planets. They found that the BAF’s present-day configuration is best explained by the breakup of a single large object (at least 100 miles across) during an asteroid belt collision about 160 million years ago.
The word “compelling”in the passage is closest in meaning to
Apersuasive
Bsubstantial
Cclear
Drevealing
5
What is the evidence that connects the Baptistina family of asteroids to the K-T impact? It is, admittedly, circumstantial, but it is compelling. The idea was proposed in a 2007 report by a group of astronomers who used computer simulations to examine how the Baptistina asteroid family(BAF for short) had evolved over time. They began by carefully mapping out the exact locations and sizes of all known objects in the family, and then, working backward, calculated how their positions have changed through time due to the gravitational pull of other bodies, including other asteroids, the Sun, and the planets. They found that the BAF’s present-day configuration is best explained by the breakup of a single large object (at least 100 miles across) during an asteroid belt collision about 160 million years ago.
According to paragraph 3， astronomers did which TWO of the following when examining how the BAF had evolved over time? To receive credit, you must select TWO answer choices.
AEstimated the size of the asteroid belt 160 million years ago
BRecorded the current locations and sizes of all known BAF objects
CStudied the breakup of large asteroids other than Baptistina
DEstimated how the gravity of other bodies would have affected the position of BAF objects
6
The calculations also showed that many fragments from the collision would have escaped the asteroid belt altogether, and some would have ended up in the vicinity of Earth. The researchers concluded that our planet must have experienced an increase in asteroid impacts for a period of about 100 million years after the collision. In fact, studies of the number and rate at which impact craters formed on the Moon and Earth had already shown this. The K-T collision took place during this period. While this does not prove that the impactor came from the Baptistina family, there is also another piece of corroborating evidence that bolsters the argument.
Paragraph 4 implies which of the following about the fragments that escaped the asteroid belt after the collision described?
AIt would have taken more than 100 million years for any of them to reach Earth.
BThere were actually more of them than researchers first realized.
CSome of them eventually collided with the Moon.
DSome later reentered the asteroid belt.
7
Spectral analysis of BAF asteroids indicates that they are composed of an uncommon type of extraterrestrial material that is especially rich in carbon; meteorites matching this composition are relatively rare in the world’s collections. However, sediments deposited at the K-T boundary contain a unique chemical marker that is specific to this carbon-rich meteorite family. Thus both the timing and composition fit. The conclusion that an asteroid “shower”generated by the breakup of Baptistina was the source of the K-T impactor seems highly likely; the astronomers who did the work estimated the probability at greater than 90 percent. They also concluded that around 20 percent of the large asteroids that are currently in the vicinity of Earth originate from the BAF.
Why does the author include the information that “sediments deposited at the K-T boundary contain a unique chemical marker that is specific”to the BAF asteroids?
ATo provide evidence that BAF asteroids are unusually rich in carbon
BTo explain why comparatively few meteorites in the world’s collections are rich in carbon
CTo explain why astronomers are reasonably sure that the K-T impactor resulted from the breakup of Baptistina
DTo identify the finding that made it possible for astronomers to calculate the probability that the breakup of Baptistina would cause an asteroid shower
8
Spectral analysis of BAF asteroids indicates that they are composed of an uncommon type of extraterrestrial material that is especially rich in carbon; meteorites matching this composition are relatively rare in the world’s collections. However, sediments deposited at the K-T boundary contain a unique chemical marker that is specific to this carbon-rich meteorite family. Thus both the timing and composition fit. The conclusion that an asteroid “shower”generated by the breakup of Baptistina was the source of the K-T impactor seems highly likely; the astronomers who did the work estimated the probability at greater than 90 percent. They also concluded that around 20 percent of the large asteroids that are currently in the vicinity of Earth originate from the BAF.
Paragraph 5 supports which of the following ideas about the unique chemical marker found in the K-T boundary sediments?
AIt formed as a result of the physical force of the K-T impact.
BIt is not normally found in large quantities on Earth.
CIt is found in most meteorites in the world’s collections.
DIt is found in Earth’s sediments after most asteroid showers.
9
What is the evidence that connects the Baptistina family of asteroids to the K-T impact? It is, admittedly, circumstantial, but it is compelling. The idea was proposed in a 2007 report by a group of astronomers who used computer simulations to examine how the Baptistina asteroid family(BAF for short) had evolved over time. They began by carefully mapping out the exact locations and sizes of all known objects in the family, and then, working backward, calculated how their positions have changed through time due to the gravitational pull of other bodies, including other asteroids, the Sun, and the planets. They found that the BAF’s present-day configuration is best explained by the breakup of a single large object (at least 100 miles across) during an asteroid belt collision about 160 million years ago. [■]
The calculations also showed that many fragments from the collision would have escaped the asteroid belt altogether, and some would have ended up in the vicinity of Earth. [■] The researchers concluded that our planet must have experienced an increase in asteroid impacts for a period of about 100 million years after the collision.[■] In fact, studies of the number and rate at which impact craters formed on the Moon and Earth had already shown this. [■] The K-T collision took place during this period. While this does not prove that the impactor came from the Baptistina family, there is also another piece of corroborating evidence that bolsters the argument.
Look at the four squaresthat indicate where the following sentence could be added to the passage
Those unable to resist Earth’s gravitational pull would have fallen through the atmosphere, with some surviving to land on the surface.
Where would the sentence best fit？Click on a square sentence to the passage.
10
It is likely that an asteroid impact caused the extinction of Earth’s dinosaurs 65 million years ago.
AUsing reflectance spectroscopy and computer simulations, astronomers determined that most of Earth’s meteorites originated beyond the asteroid belt, which lies between Mars and Jupiter.
BResearchers have calculated that an asteroid belt collision occurring about 160 million years ago may have begun the chain of events that led to the asteroid impact and K-T extinction.
CReflectance spectroscopy, which uses light reflected from an object to analyze its composition, shows that K-T boundary sediments and BAF asteroids share chemical aspects.
DHaving discovered that the asteroid Baptistina was once much larger than it is today, Auguste Charlois was the first to consider a connection between the BAF and the K-T extinction.
EAfter the breakup of the asteroid from which Baptistina originated, many fragments escaped the asteroid belt, greatly increasing Earth impacts and leaving some BAF asteroids near Earth.
FDespite the carbon-rich soils at impact sites and the high number of asteroids originating from the BAF, few astronomers are willing to draw conclusions about the K-T impactor’s source.
