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Passage I - Mass extinctions on Earth may be caused by bombard-ments (September 2023 - G01)
Passage I
Mass extinctions on Earth may be caused by bombard-ments of Earth by comets from the Oort cloud, a sphericalswarm of comets occupying the outer part of our solarsystem. Three scientists share their viewpoints about possi-ble causes of the bombardments.
Scientist 1
The Sun is orbited by a dim, unseen object called abrown dwarf, an object that is less than 0.08 times theSun’s mass and therefore is not massive enough to becomea star. Each complete orbit of the brown dwarf takes26 million years. Once each orbit, the brown dwarf passesthrough the Oort cloud. The brown dwarf’s gravitationalforce alters the orbits of many comets, causing 1 or moreof them to enter the inner part of the solar system and tocollide with Earth, producing a mass extinction.
Scientist 2
The Sun is part of an open cluster, a type of star clus-ter in which the stars are bound to each other by gravity.The Sun revolves around the center of mass of the clusteronce every 26 million years. Once every orbit, the Sunpasses through the densest part of the cluster. The gravita-tional force exerted by the stars in this part of the clustercauses many comets to leave the Oort cloud. One or moreof these comets enter the inner part of our solar system andcollide with Earth, causing a mass extinction.
Scientist 3
Our galaxy is disk shaped, and the Sun lies within thedisk. The galaxy also contains high-velocity stars, stars following orbits that are highly inclined with respect to thedisk. The bombardments that produce mass extinctions arecaused by the gravitational effects of high-velocity stars.High-velocity stars cause bombardments whenever thesestars pass near the Oort cloud. This hypothesis is prefer-able because, rather than occurring every 26 million years,mass extinctions occur at irregular intervals. Moreover, theSun cannot be part of an open cluster, because the Sun is5 billion years old. The stars in open clusters all form atapproximately the same time and then drift apart after afew hundred million years.
Questions from Passage I
1) Based on Scientist 3’s viewpoint, which of the follow-ing quantities is approximately equal for the stars in anopen cluster?
A. Mass
B. Diameter
C. Age
D. Temperature
2) Based on Scientist 3’s viewpoint, high-velocity starspass through or near our solar system:
F. at irregular intervals.
G. once each year.
H. every 13 million years.
J. every 26 million years.
3) Suppose that the last mass extinction occurred 13 million years ago. Based on Scientist 1’s viewpoint, the nextmass extinction would most likely occur how many million years from now?
A. 5
B. 13
C. 26
D. 32
4) Scientist 1 implies that the unseen object might beobservable from Earth if the object:
F. orbited the center of an open cluster instead of the center of our galaxy.
G. orbited the center of our galaxy instead of the center of an open cluster.
H. were a star instead of a brown dwarf.
J. were a brown dwarf instead of a star.
5) The viewpoints of Scientists 1 and 2 are inconsistentwith that of Scientist 3 regarding which of the follow-ing factors?
A. How regularly brown dwarfs form
B. Whether comets cause mass extinctions at regularintervals of time
C. Whether Earth has been bombarded by extraterres-trial objects at any time in the past
D. Whether mass extinctions will occur in the future
6) Proving that the Sun is a member of an open clusterwould directly contradicta statement made by:
F. Scientist 1 only.
G. Scientist 3 only.
H. Scientists 1 and 3.
J. Scientists 2 and 3
7) The stars in an open cluster are bound together bygravity. Scientist 3 supports the conclusion that thegravitational force of an open cluster is:
A. strong enough to keep the cluster together indefinitely.
B. too weak to keep the cluster together indefinitely.
C. present only among the stars more massive than the Sun.
D. present only among the stars less massive than the Sun.
Solution
Correct answer:
1 - C
2 - F
3 - B
4 - H
5 - B
6 - G
7 - B
1) C. Age (According to Scientist 3, stars in an open cluster form at roughly the same time.)
2) F. at irregular intervals (Scientist 3 argues extinctions are not regular and high-velocity stars cause them at various times.)
3) B. 13 (Scientist 1 suggests the brown dwarf disrupts the Oort cloud every 26 million years. 26 - 13 = 13)
4) H. were a star instead of a brown dwarf (Stars are bright, brown dwarfs are not. A bright object might be seen.)
5) B. Whether comets cause mass extinctions at regular intervals of time (Scientists 1 & 2 say regular, Scientist 3 says irregular.)
6) G. Scientist 3 only (Scientist 3 claims the Sun can't be in an open cluster due to age.)
7) B. too weak to keep the cluster together indefinitely (Since stars eventually drift apart, the cluster isn't forever stable.)
Exam Edition: September 2023 - G01
Exam Year: 2023
Related topics: Star formation and evolution, Solar system and transneptunian objects, Astronomy