AccelePrep for the ACT Test 2nd Edition Student Text

182 • S URGE TO S UCCESS ! S CIENCE T EST P REP

POWER PRACTICE 1 DIRECTIONS: Give yourself six minutes to work –Š”‘—‰Š –Š‡ ˆ‘ŽŽ‘™‹‰ ‘ϐŽ‹…–‹‰ ‹‡™’‘‹–• ’ƒ••ƒ‰‡ ƒ† ƒ……‘’ƒ›‹‰ “—‡•–‹‘•Ǥ ”‡˜‹‡™ the passage, and then move quickly to the questions to determine where you need focus your attention. How old is the earth? Two opposing views are presented. Scientist 1 Š‡ ‡ƒ”–Š ‹• ƒ’’”‘š‹ƒ–‡Ž› ϐ‹˜‡ „‹ŽŽ‹‘ ›‡ƒ”• old. We know this to be true because of radioactive dating. Some chemical elements are unstable and will fall apart into smaller pieces over time. This disintegration occurs over a period of time that is very regular for the particular element. In general, we talk about the half-life of the element, which is the time necessary for one-half of the material to disintegrate. This time is constant whether we have an ounce or a ton of the material. So, by measuring the relative amounts of the material left and the disintegration products, we can form an accurate idea of how old the earth is by determining how many half-lives have occurred. Scientist 2 The argument that supports the hypothesis –Šƒ– –Š‡ ‡ƒ”–Š ‹• ‘Ž› ϐ‹˜‡ „‹ŽŽ‹‘ ›‡ƒ”• ‘Ž† ‹• •‡”‹‘—•Ž› ϐŽƒ™‡†Ǥ Šƒ– –Š‡ ƒ”‰—‡– ˆƒ‹Ž• –‘ take into account is that the earth is the constant recipient of a shower of cosmic debris in the form of meteorites. These meteorites replenish the stock of radioactive material on the surface of the earth, making it seem as though the earth has gone through fewer half-lives than it really has. Therefore, all estimates of the age of the earth based on radioactive dating are too low. 1. Which of the following is a major assumption of Scientist 1? A. The earth has life that recycles carbon-14. B. The half-life of all radioactive elements is ϐ‹˜‡ „‹ŽŽ‹‘ ›‡ƒ”•Ǥ C. The radioactive material was formed at the same time as the earth. D. There is no longer any radioactivity on the earth.

2. Which of the following is a major assumption of Scientist 2? F. The meteorites that land on the earth are radioactive. G. Few meteorites have landed on the earth. Ǥ Š‡ ‡ƒ”–Š ‹• ‘”‡ –Šƒ ϐ‹˜‡ „‹ŽŽ‹‘ ›‡ƒ”• ‘Ž†Ǥ J. The earth is highly radioactive. 3. Which of the following, if true, would best refute Scientist 2’s argument? A. Recent meteorites have been found to be radioactive. B. The earth has a greater amount of radioac- tive material on the surface than in the mantle. C. The earth’s orbit intersects the orbits of a number of meteorites. D. Few meteorites have been found to contain radioactive material. 4. Which of the following would be most likely if Scientist 2’s hypothesis were correct? F. The total amount of radioactive material and its disintegration products on the earth has decreased over time. G. The total amount of radioactive material and its disintegration products has increased over time. H. The total amount of radioactive material and its disintegration products has stayed essentially the same over time. J. The earth will reach a critical mass and explode. 5. Which of the following would be most likely if Scientist 1’s hypothesis were correct? A. The total amount of radioactive material and its disintegration products has decreased over time. B. The total amount of radioactive material and its disintegration products has increased over time. C. The total amount of radioactive material and its disintegration products has stayed essentially the same over time. D. The earth will reach a critical mass and explode.