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A primary value in early twentieth-century Modernist architectural theory was that of "truth to materials", that is, it was essential that a building's design express the "natural" character of the building materials. This emphasis would have puzzled the architects of the Italian Renaissance (sixteenth century), a period widely regarded as the apex of architectural achievement, for Renaissance architects' designs were determined only minimally by the materials employed.

The diversity of Italy's natural resources provided Renaissance architects with a wide variety of building materials. The builders of the Pitti Palace (1558-1570) used great blocks of Tuscan stone, just as Etruscans living in the same part of Italy had done some twenty centuries earlier. Had the Florentine Renaissance builders aped the Etruscan style, it might be said that their materials determined their style, since Etruscan style matched the massive, stark, solid character of the stone. But these same materials, which so suited the massive Etruscan style, were effectively used by the Florentine Renaissance to create the most delicate and graceful of styles.

A similar example of identical materials used in contrasting styles characterizes the treatment of Roman travertine marble. When Baroque architects of seventeenth-century Rome desired a massive and solid monumental effect, they turned to travertine marble, whose "natural effect" is, indeed, that of spacious breadth and lofty, smoothly rounded surfaces. Yet during the Renaissance, this same material had been used against its "nature," in the Florentine tradition of sharply carved detail. Italian Renaissance architecture was shaped less by the "nature" of the materials at hand than by the artistic milieu of Renaissance Italy, which included painting and sculpture as well as architecture. While Roman travertine marble may have lent itself to fine carving, the Florentine passion for fine detail is no less marked in Florentine Renaissance painting than in Florentine Renaissance architecture. Similarly, in the next century, the emphasis on shading and corporeal density in Baroque painting mirrored the use of Roman travertine marble in Baroque architecture to create broad shadow and powerful masses.

The ingenuity of Renaissance architects extended beyond merely using a material in a way not suggested by its outward natural appearance. If they conceived a design that called for a certain material either too expensive or difficult to work with, they made no scruple about imitating that material. Their marbles and their stones are often actually painted stucco. When the blocks of masonry with which they built were not in scale with the projected scheme, the real joints were concealed and false ones introduced. Nor were these practices confined, as some scholars insist, to the later and supposedly decadent phases of the art. Material, then, was utterly subservient to style.
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(paragraph 2)?
In the second paragraph, the author is primarily concerned with

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