<p>(1) One of the big problems for geologists has always been determining the age of the fossils and other materials they find underground. (2) One method of wide usage is carbon-14 dating. (3) Carbon-14 dating is pretty straightforward. (4) Carbon-14 is a harmless radioactive material found in the Earth’s atmosphere. (5) Animals and plants absorb carbon-14 into their tissues while they are alive. (6) After they die, however, they cease to absorb carbon-14, and the carbon-14 in their tissues begins to decay. (7) The process of decay that makes carbon-14 dating possible. (8) Scientists who study radioactive material like carbon-14 have developed the term “half-life.” (9) The “half-life” of a substance is the amount of time it takes for half of the atoms in a sample to decay. (10) Different radioactive materials have half-lives ranging from seconds to thousands of years. (11) Carbon-14 has a half-life of 5730 years.</p>
<pre><code>(12) A scientist named Willard Libby was the first person to use carbon-14 dating, in 1949. (13) Libby used the concept of “half-life” to determine that plant and animal remains containing half the amounts of carbon-14 expected in a living specimen were 5730 years old. (14) Those remains containing less than half the expected amounts were older; the ones that contained more than half were younger.
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<p>The main purpose of paragraph 2 is to</p>
<p>(A) present a memorable example
(B) summarize previous information
(C) identify a common misconception
(D) explain a puzzling contradiction
(E) introduce an important concept</p>
<p>First of all, it’s weird that this is an Improving Paragraphs question. Secondly, isn’t “half-life” a concept INTRODUCED in paragraph 1??? That’s the reason I choose A (which I didn’t completely feel comfortable with) instead of E.</p>