GRE Reading Comprehension

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Source: XDF

Shergottites, the name given to three anomalous achondrites (igneous meteorites lacking chondrules) so far discovered on Earth, present scientists with a genuine enigma. Shergottites crystallized from molten rock less than 1.1 billion years ago (some 3.5 billion years later than typical achondrites) and were presumably ejected into space when an object impacted on a body similar in chemical composition to Earth. While some scientists speculate that shergottites derive from Io (a volcanically active moon of Jupiter), recent measurements suggest that since Io's surface is rich in sulfur and sodium, the chemical composition of its volcanic products would probably be unlike that of the shergottites. Moreover, any fragments dislodged from Io by interbody impact would be unlikely to escape the gravitational pull of Jupiter.

The only other logical source of shergottites is Mars. Space-probe photographs indicate the existence of giant volcanoes on the Martian surface. From the small number of impact craters that appear on Martian lava flows, one can estimate that the planet was volcanically active as recently as a half-billion years ago—and may be active today.

Question List: 1 2

The passage provides information to answer which of the following questions?

  • A What is the precise age of the solar system?
  • B How did shergottites get their name?
  • C What are the chemical properties shared by shergottites and Martian soils?
  • D How volcanically active is the planet Jupiter?
  • E What is a major feature of the Martian surface?

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