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  3. For many years, scientists couldn’t figure out how atoms and molecules combined to make living things. Plants, fish, dinosaurs,

For many years, scientists couldn’t figure out how atoms and molecules combined to make living things. Plants, fish, dinosaurs,

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问题    For many years, scientists couldn’t figure out how atoms and molecules combined to make living things. Plants, fish, dinosaurs, and people are made of atoms and molecules, but they are put together in a more complicated way than the molecules in the primitive ocean. What’s more, living things have energy and can reproduce, while the chemicals on the Earth 4 billion years ago were lifeless.
   After years of study, scientists figured out that living things, including human bodies, are basically made of amino acids, nucleotide bases, lipids and water. How could such complicated molecules have been formed and have started to interact in the primitive soup? Scientists were stumped.
   Then, in 1953, two scientists named Harold Urey and Stanley L. Miller did a very simple experiment to find out what had happened on the primitive Earth. They set up some tubes and bottles in a closed loop, and put in some of the same gases that were present in the atmosphere 4 billion years ago — water vapour, ammonia, carbon dioxide, methane, and hydrogen.
   Then they shot an electric spark through the gases to simulate bolts of lightning on the ancient Earth, circulated the gases through some water, sent them back for more sparks, and so on. After several days, the water that the gases had been bubbling through turned brown. Some new chemicals were dissolved in it. When Miller and Urey analyzed the liquid, they found that it contained amino acids — the very kind of molecules found in all living things.
选项 A、4 billion years ago.
B、After seven days.
C、Many years ago.
D、In 1953.
答案D
解析
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