16. The primary purpose of the passage is to

(A) identify differing approaches
(B) discount a novel trend
(C) advocate traditional methods
(D) correct misinterpretations
(E) reconcile seeming inconsistencies

　　　Since the early 1920s, most petroleum¹ geologists² have favored a 　biogenic theory for the formation of oil. According to this theory, organic 　matter became buried in sediments³, and subsequent conditions of 　temperature

(5) and pressure over time transformed it into oil.

　　　Since 1979 an opposing abiogenic theory about the origin of oil has been 　promulgated⁴. According to this theory, what is now oil began as hydrocarbon⁵ 　compounds within the earth s mantle⁶ (the region

(10) between the core and the crust) during the formation of the earth. Oil was 　created when gasses rich in methanc, the lightest of the hydrocarbons⁷, rose 　from the mantle through fractures and fauhs in the crust, carrying a significant 　amount of heavier hydrocarbons with them.

(15) As the gases encountered intermittent⁸ drops in pressure, the heavier 　hydrocarbons condensed, forming oil, and were deposited in reservoirs 　throughout the crust, Rock regions deformed⁹ by motions of the crustal plates 　provided the conduits and fracures necessary for the

(20) gases to rise through the crust.

　　　Opponents of the abiogenic theory charge that hydrocarbons could not 　exist in the mantle, because high lemperatures would destroy or break them 　down. Advocates of the theory, however, point out that other

(25) types of carbon exist in the mantle: unoxidized carbon must exist there, 　because diamonds are formed within the mantle before being brought to the 　surface by eruptive processes. Proponents¹⁰ of the abiogenic theory also point 　to recent experimental work that suggests

(30) that the higher pressures within the mantle tend to offset¹¹ the higher 　temperatures, allowing hydrocarbons, like unoxidized carbon, to continue to 　exist in the mantle.

　　　If the abiogenic theory is correct, vast undiscovered

(35) reservoirs of oil and gas—undiscovened because the biogenic model 　precludes¹² their existence—may in actuality exist. One company owned by 　the Swedish government has found the abiogenic theory so persuasive¹³ that it 　has started exploratory drilling for gas

(40) or oil in a granite¹⁴ formation called the Siljan Ring—not the best place to 　look for gas or oil if one belives they are derived¹⁵ from organic compounds, 　because granite forms from magma (molten rock) and contains no organic 　sediments. The ring was formed about 360

(45) million years ago when a large meteorite¹⁶ hit the 600-million-year-old granite 　that forms the base of the continental¹⁷ crust. The impact fractured the granite, 　and the Swedes believe that if oil comes from the mantle, it could have risen 　with methane¹⁸ gas through this now

(50) permeable rock. Fueling their optimism further is the fact that prior to the 　start of drilling, methane gas had been detected rising through the granite.

17. Which one of the following statements best expresses the main idea of the passage?

(A) Although the new abiogenic theory about the origin of oil is derived from the 　　conventional biogenic theory, it suggests new types of locations for oil 　　drilling.
(B) The small number of drilling companies that have responded to the new 　　abiogenic theory about the origin of oil reflects the minimal¹⁹ level of 　　acceptance the theory has met with in the scientific community.
(C) Although the new abiogenic theory about the origin of oil fails to explain 　　several enigmas²⁰ about oil reservoirs, it is superior to the conventional 　　biogenic theory.
(D) Although it has yet to receive either support or refutation by data gathered 　　from a drilling project, the new abiogenic theory about the origin of oil offers 　　a plausible²¹ alternative to the conventional biogenic theory.
(E) Having answered objections about higher pressures in the earth s core, 　　proponents of the new abiogenic theory have gained broad acceptance for 　　their theory in the scientific community.

18. Which one of the following best describes the function of the third paragraph?

(A) It presents a view opposed to a theory and points out an internal 　　contradiction in that opposing view.
(B) It describes a criticism of a theory and provides countervailing evidence to 　　the criticism.
(C) It identifies a conflict between two views of a theory and revises both views.
(D) It explains an argument against a theory and shows it to be a valid²² criticism.
(E) It points out the correspondence between an argument against one theory 　　and arguments against similar theories.

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