GRE Exam Dumps : GRE General Test

Even the most complex models used in fishery management are cartoons of reality. They reduce hundreds of links in food webs to a handful and inadequately represent processes operating over space. Many of their assumptions are as flawed today as those of the simplest models of the past. Fish stocks, for one. are still assumed to be populations of a species that are isolated from one another. Yet many populations mix at their edges and some even migrate through areas occupied by other populations. Furthermore, the more complex models suffer from a "crisis of complexity"—more is really less. Adding layers of detail, each carrying its own set of assumptions, produces instability. The model's behavior becomes erratic, and conclusions drawn from it can be downright misleading.

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Age data from meteorites suggests that, in contrast to the relatively_________pace of planetary evolution we are

witnessing today, the first ten million years or so of our solar system history were extremely eventful.

Instances of "galactic cannibalism"—mergers in which large galaxies completely consume smaller ones—may be fairly common. Tidal forces produced by the Milky Way's powerful gravity, for example, appear to be dismantling and engulfing a dwarf galaxy in the constellation Sagittarius, producing large clumps and streamers of stars connecting the two galaxies. Astronomers have also observed two dense clusters of stars and gas at the heart of the Andromeda galaxy, an apparent "double nucleus" that may contain the remnant of a cannibalized dwarf galaxy. But this twin-lobed appearance could also be created by two parts of a single nucleus bisected by a lane of dust. Scientists believe that only about 25 percent of such apparent double nuclei actually represent galactic cannibalism. Many of the rest result from the illusion of proximity that occurs when objects at different distances appear along the same line of sight: others consist of debris from galactic "collisions." in which one galaxy has passed through another without merging, causing waves of new star formation.

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