中央民族大学2005年招收攻读博士学位生入学考试(10)

考博试题

[D] was based on economic reasoning.

45. The author writes this text to

[A] present Professors McCloskey and Ziliak’s latest work.

[B]inform people that statistic figures are not reliable.

[C] show that too many economists misuse statistics

[D] argue that numbers and economic reasoning are equally important. Passage 3

As NASA prepares to set twin robots loose on the Martian surface and makes plans to send another in 2007, the agency’s long term goal is clear: Determine whether the red planet does or over did harbor life.

But the current search for life is necessarily limited to life as we know it, organisms

dependent on liquid water. A reader recently suggested that “we as humans are arrogant, simply believing that any other form of life will be just like us.”

Researchers devoted to the search for extraterrestrial (ET) have a similar view. “Scientists” approach to finding life is very Earth-centric”, says Kenneth Nealson, a geobiologist at the University of Southern

California. “Based on what we know about life on Earth, we set the limits for where we might look on other planets”, Nealson said. Within that framework, however, there are extreme cases of life on Earth that suggest the range of places to look on frigid Mars. Nealson and his colleagues recently found the most extreme sort of organism in a salty liquid lake under the permafrost of Siberia. The organism, named cryopegella, can exist at colder temperatures than any previously discovered. Nealson’s team figures that if the ice at the polar caps of Mars warmed to liquid water, organisms like cryopegella could have awakened and repaired any damage that might have occurred to their various cellular components. That does not mean there are necessarily dormant microbes within the ice caps of Mars. But it does suggest a broader range of potential cradles for life.

Other researchers agree, and a host of so-called “extremophile” discoveries on Earth in recent years indicate the polar regions of Mars might be prime hunting grounds. As on Earth, organisms there might be slathered in natural antifreeze or be able to go dormant for tens of thousands of years. Waiting for a brief thaw, their moment in the Sun.

Meanwhile, scientists recognize that there could indeed be life elsewhere in the universe that does not require water. And some astrobiologists are trying to explore the possibilities.