Massive projectiles striking much larger bodies create various kinds of craters, including multi-ring basins–the largest geologic features observed on planets and moons. In such collisions, the impactor is completely destroyed and its material is incorporated into the larger body. Collison's between bodies of comparable size, on the other hand, have very different consequences: one or both bodies might be entirely smashed, with mass from one or both the bodies redistributed among new objects formed from the fragments. Such a titanic collision between Earth and a Mars-size impactor may have given rise to Earth's Moon.
The Earth-Moon system has always been perplexing. Earth is the only one of the inner planets with a large satellite, the orbit of which is neither in the equatorial plane of Earth nor in the plane in which the other planets lie. The Moon's mean density is much lower than that of Earth but is about the same as that of Earth's mantle. This similarity in density has long prompted speculation that the Moon split away from a rapidly rotating Earth, but this idea founders on two observations. In order to spin off the Moon, Earth would have had to rotate so fast that a day would have lasted less than three hours. Science offers no plausible explanation of how it could have slowed to its current rotational rate from that speed. Moreover, the Moon's composition, though similar to that of Earth's mantle, is not a precise match. Theorizing a titanic collision eliminates postulating a too-rapidly spinning Earth and accounts for the Moon's peculiar composition. In a titanic collision model, the bulk of the Moon would have formed from a combination of material from the impactor and Earth's mantle. Most of the earthly component would have been in the form of melted or vaporized matter. The difficulty in recondensing this vapor in Earth's orbit, and its subsequent loss to the vacuum of outer space, might account for the observed absence in lunar rocks of certain readily vaporized compounds and elements.
Unusual features of some other planets might also be explained by such impacts. Mercury is known to have a high density in comparison with other rocky planets. A titanic impact could have stripped away a portion of its rocky mantle, leaving behind a metallic core whose density is out of proportion with the original ratio of rock to metal. A massive, glancing blow to Venus might have given it its anomalously slow spin and reversed direction of rotation. Such conjectures are tempting, but, since no early planet was immune to titanic impacts, they could be used indiscriminately to explain away in a cavalier fashion every unusual planetary characteristic; still, we may now be beginning to discern the true role of titanic impacts in planetary history.
|
|
According to the passage, which of the following is true of the collisions mentioned in the highlighted sentence?
|
|
The author of the passage asserts which of the following about titanic collision models?
|
|
The passage suggests that which of the following is true of the cited "compounds and elements"?
|
|
In the second paragraph, the author is primarily concerned with
|
As it was published in 1935, Mules and Men, Zora Neale Hurston's landmark collection of folktales, may not have been the book that its author first had in mind. In this anthropological study, Hurston describes in detail the people who tell the stories, often even inserting herself into the storytelling scene. Evidently, however, Hurston had prepared another version, a manuscript that was recently discovered and published after having been forgotten since 1929. This version differs from Mules and Men in that it simply records stories, with no descriptive or interpretive information.
While we cannot know for certain why Hurston's original manuscript went unpublished during her lifetime, it may have been because publishers wanted something more than a transcription of tales. Contemporary novelist and critic John Edgar Wideman has described Black literature as the history of a writing that sought to escape its frame, in other words, as the effort of Black writers to present the stories of Black people without having to have a mediating voice to explain the stories to a non-Black audience. In this, Hurston may have been ahead of her time.
|
|
Select the sentence that suggests a possible reason why Hurston wrote the version of Mules and Men that was published in 1935.
|
|
The passage suggests that Hurston may have done which of the following in preparing her original version?
|
|
My grandma has a strong belief in all things _____: she insists, for example, that the house in which she lived as a child was haunted.
|
|
Now that photographic prints have become a popular field for collecting, auctions are becoming more (i)_____. It is not just the entry of new collectors into the field that is causing this intensification. Established collectors' interests are also becoming more (ii)_____. Those who once concentrated on the work of either the nineteenth-century pioneers or the twentieth-century modernists are now keen to have (iii)_____ collections.
|
|
The beauty of the scientific approach is that even when individual researchers do _____ bias or partiality, others can correct them using a framework of evidence on which everyone broadly agrees.
|
|
The reconstruct known work is beautiful and also probably _____: it is the only Hebrew verse written by a woman.
|
|
In a book that inclines to _____, an epilogue arguing that ballet is dead arrives simply as one more overstatement.
|
|
The skin of the poison dart frog contains deadly poisons called batrachotoxins. But the (i)_____ of the toxins has remained an enigma, as the frog does not (ii)_____ them. Now an analysis suggests that the melyrid beetle is the source. Collected beetle specimens all contained batrachotoxins, suggesting that these beetles are (iii)_____ by the frogs.
|
|
Although trains may use energy more (i)_____ than do automobiles, the latter move only when they contain at least one occupant, whereas railway carriages spend a considerable amount of time running up and down the tracks (ii)_____, or nearly so.
|
|
Most capuchin monkey conflict involves such a (i)_____ repertoire of gestural and vocal signals that it is difficult for researchers to tease apart the meanings of the individual signals. This (ii)_____ is (iii)_____ by the fact that many signals seem to shift in meaning according to the context in which they are produced and the developmental stage of the individuals producing them.
|
