Scientists studying Mars long thought the history of its crust was relatively simple. One reason for this is that geologic

Question

Scientists studying Mars long thought the history of its crust was relatively simple. One reason for this is that geologic and climate data collected by a spacecraft showed that the crust was largely composed of basalt, likely as a result of intense volcanic activity that brought about a magma ocean, which then cooled to form the planet’s surface. A study led by Valerie Payré focused on additional information—further analysis of data collected by the spacecraft and infrared wavelengths detected from Mars’s surface—that revealed the presence of surprisingly high concentrations of silica in certain regions on Mars. Since a planetary surface that formed in a mostly basaltic environment would be unlikely to contain large amounts of silica, Payré concluded that blank

Which choice most logically completes the text?

Accepted Answer

Choice D is the best answer. Cooling magma would create basalt, but &ldquo;a planetary surface that formed in a mostly basaltic environment would be unlikely to contain large amounts of silica.&rdquo; Since Mars&rsquo;s crust does contain large amounts of silica, it is unlikely that Mars&rsquo;s crust was formed exclusively by cooling magma. Therefore, there were likely other major geological events that created the high silica concentrations. Choice A is incorrect. Although the passage discusses these two methods of collecting data about Mars&rsquo;s crust, it never compares their reliability, so there&rsquo;s no basis for this inference. Choice B is incorrect. The passage never mentions anything about the crusts of other planets, so there&rsquo;s no basis for this inference. Choice C is incorrect. The passage never mentions Earth&rsquo;s crust, so there&rsquo;s no basis for this inference.

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