Victory for the ACT Student Text 15e

S CIENCE R EVIEW • 349

Passage VI How did life originate on planet Earth? Two opposing views are presented. Scientist 1 The idea that Earth could have given rise to life independently is incorrect. Life on this planet must have come from elsewhere for several reasons. First of all, complex life appears very suddenly in the geological record. Secondly, all life on Earth has a very similar biochemistry. If life originated on Earth, one would expect regional variations in biochemistry, similar to the variations in species spread over large areas. Finally, the –‹‡ ™Š‡ Ž‹ˆ‡ ϐ‹”•– ƒ’’‡ƒ”‡† ‹ –Š‡ ‰‡‘Ž‘‰‹…ƒŽ record was also a time when large numbers of meteorites struck Earth. The meteorites must have caused life to appear on Earth. The simplest hypothesis is that the meteorites brought life with them. Scientist 2 Life need not have been imported from outer space. The chemicals required for life existed on the surface of Earth at the time Ž‹ˆ‡ ϐ‹”•– ƒ’’‡ƒ”‡†Ǥ Š‡ ˆƒ…– –Šƒ– ƒŽŽ Ž‹ˆ‡ Šƒ• ƒ similar biochemistry can be explained because any group of chemicals that won the race to life would probably have used the same “almost-living” chemicals as food. Since we can offer explanations for what happened without relying on a meteorite of unknown composition that might have fallen to Earth, we should stick to hypotheses that have fewer unknowns. 34. Which of the following is an assumption of Scientist 1? F. Complex life forms can develop quickly. G. Meteorites burn up as soon as they hit Earth’s atmosphere. H. There is a cause-and-effect relationship between meteors falling and the origin of life. J. The changes on Earth’s surface due to the presence of life attracted meteor showers.

Which of the following, if true, most strengthens Scientist 2’s argument? Ǥ Ž› ϐ‹˜‡ ’‡”…‡– ‘”‡ ‡–‡‘”• –Šƒ normal fell on Earth during the time life began. Ǥ Ž› ϐ‹˜‡ ’‡”…‡– ‘ˆ –Š‡ ‡–‡‘”‹–‡• studied contained organic molecules. C. A simulation of early Earth chemistry showed the spontaneous formation of complex biomolecules. D. Meteorites containing amoebas have been found. Which of the following, if true, most strengthens Scientist 1’s argument? F. No meteors fell to Earth during the time life began. G. Meteorites studied did not contain molecules necessary to form life. H. A simulation of early Earth chemistry showed the spontaneous formation of complex biomolecules. J. Meteorites containing amino acids have been found. With which explanation of the similar biochemistry of all life on Earth would Scientist 1 most likely agree? A. A single chemical pathway to life exists. B. Life on Earth arose from a single source. C. Life on Earth is not varied. D. Meteors are simple. With which explanation of the similar biochemistry of all life on Earth would Scientist 2 most likely agree? F. A single chemical pathway to life exists. G. Life on Earth arose from a single source. H. Life on Earth is not varied. J. Meteors are simple.

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Passage Perfect For strengthen- the-argument questions, it is important to think about the central assumption of the argument. Which statement most validates this assumption? For example, in Scientist 2’s argument, the assumption is that meteorites actually could bring life with them. Which statement addresses this assumption?

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