Question 47 Answer and Explanation _ACT April 2014 Form 71H English Section

Passage IV

Radiocarbon Dating,Tree Rings, and the Distant Past

[1]

Radiocarbon dating, developed by Willard F. Libby in the 1940s, seemed to offer archaeologists a definitive method for determining the age of artifacts. The method for archaeologists to date artifacts was based on the amount of radioactive carbon 14 found in organic matter such as wood, bones, and shells. [A] A living organism absorbs carbon 14 until the moment it dies, at which point the amount of carbon 14 in an organism starts to decay to nitrogen 14. Carbon 14's half-life (47) is 5,730 years. Therefore, as long as even the smallest amount of carbon 14 is present; radiocarbon dating can date an artifact by calculating its ratio of carbon 14 to nitrogen 14. [B]

[2]

However, questions were arisen at the time about the method's accuracy. The data from radiocarbon dating conflicted with long-established theories archaeologists had developed on the basis of Egyptian dynastic records. [C]

[3]

Even though Libby won the Nobel Prize in 1960, experts realizing, they needed another method to corroborate Libby's findings. They turned to a much older dating method; dendrochronology, the use of tree rings for mapping intervals of time. [D] Working together, experts in both methods dated thousands of wood samples from bristlecone pines, some of which share habitats with Douglas firs and piñon pines. When plotted on a graph called a calibration curve, these data with calendar dates provided a method for correlating radiocarbon dates.

[4]

The radiocarbon dates, now verified as accurate, overturned conventional thinking in archaeology and proved that dating methods based on Egyptian records were inaccurate. (57) Some stone monuments in Europe, for example, were found to be up to 800 years older than the Egyptian and Greek structures that had supposedly inspired them. These findings lead to the establishment of different facts and things about many places, such as Stonehenge and the stone temples of Malta.

47. At this point, the writer is considering adding the following accurate information:

(the time it takes for half of the carbon 14 to decay to nitrogen 14)

Should the writer make this addition here?

A. Yes, because it explains the interaction between carbon 14 and nitrogen 14 during an organism's lifetime.

B. Yes, because it provides a definition of the term carbon 14's half-life.

C. No, because it doesn't explain how scientists discovered this information.

D. No, because it's not relevant to the main point of the sentence.

Answer and Explanation

Your Answer is

Correct Answer is B

Explanation

The detail of "the time when half of carbon14 decays into nitrogen14" explains the previous noun (carbon 14's half-life), so it cannot be removed. The mistake in item A is that the added sentence did not mention interaction (interaction). This sentence only said carbon decay to nitrogen14, and did not reflect the interaction between the two.