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第16~20 題為一題組Everyone seems to agree that the Earth was a violent place with volcanic eruptions, lightning and torrential rains. Therewas little if any free oxygen and no layer of ozone to absorb the ultraviolet radiation from the Sun. By its photochemical action,the radiation may have helped to keep the atmosphere rich in reactive molecules and far from chemical 16 . Certainly, thefirst living systems were much simpler than any cells alive today. The transition from nonliving to living was gradual, and nosingle event led to life in all the modern 17 .There are two major scientific theories regarding how life came to be on Earth. It either evolved on Earth from nonlivingchemicals, or elsewhere in the universe and was brought to Earth by comets or meteorites. Amino acids and other 18 havebeen found in meteorites, and so chemical evolution of these molecules might have been—and till may be—widespread in thecosmos.In May 1953, the graduate student Stanley Miller used a reflux apparatus to reproduce ancient atmospheric condition thatexisted prior to the chemical evolution of biological molecules. To do this, Miller recirculated water, vapor, and other gases(CH4, NH3 and H2) through a chamber where they were exposed to a continuous high voltage electrical discharge that 19natural lightning. After a few days, the mixture was analyzed and found to contain some of the building blocks for life, nucleicacids. However, nucleic acids (DNA, RNA) themselves were not formed! The experiment also produced compounds whichwould be 20 to most life forms. But these compounds, which include formaldehyde and cyanide, are necessary for creatingimportant biochemical compounds, including amico acids.(AB) precursors (AC) insolvency (AD) equilibrium (AE) simulated (BC) proliferating (BD) complexity(BE) venomous
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