16. The primary purpose of the passage is to
identify differing approaches
discount a novel trend
advocate traditional methods
correct misinterpretations
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
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 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.
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
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
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
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
reservoirs of oil and gasundiscovened because the biogenic model precludes12 their existencemay 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
or oil in a granite14 formation called the Siljan Ringnot the best place to look for gas or oil if one belives they are derived15 from organic compounds, because granite forms from magma and contains no organic sediments. The ring was formed about 360
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
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?
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.
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.
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.
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.
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?
It presents a view opposed to a theory and points out an internal contradiction in that opposing view.
It describes a criticism of a theory and provides countervailing evidence to the criticism.
It identifies a conflict between two views of a theory and revises both views.
It explains an argument against a theory and shows it to be a valid22 criticism.
It points out the correspondence between an argument against one theory and arguments against similar theories.
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