PrepTest 142, Section 1, Question 23
Geologist: The dominant view that petroleum formed from(61 more words not shown)
Which one of the following,(7 more words not shown)
- AFossils have been(6 more words not shown)
- BLiving organisms only(6 more words not shown)
- CIt would take(9 more words not shown)
- DCertain strains of(7 more words not shown)
- ESome carbon deposits(8 more words not shown)
Reading the argument
Biomarkers tell us that life was present. Do they tell us how the petroleum formed?
Suppose petroleum already existed deep underground and biological material entered it later. The biomarkers would then be evidence of that later contact, not necessarily evidence that plants and animals supplied the original material. Perhaps the molecules could seep down into a preexisting deposit.
What we’re looking for
The geologist treats their presence as enough to refute the deep-carbon explanation. To weaken that argument, give us another way the biomarkers could get there. We don't need to establish which origin theory is ultimately correct. We need to show why this particular evidence doesn't settle the origin.
Working the answers
- A
Fossils without biomarkers tell us that the absence of these molecules needn't rule out an organic source. But our evidence runs the other way: biomarkers are present. We need to know whether that presence could occur without petroleum having formed from living material. A doesn't provide that alternative route.
- B
Living organisms appearing later than the earth doesn't tell us when biomarkers entered petroleum. Life could arise after a carbon deposit formed and then leave traces in it. The timing of life's emergence alone doesn't establish how the petroleum formed or explain the observed molecules.
- C
A long formation process doesn't show that the necessary time was unavailable. More importantly, it doesn't address whether biomarkers could enter petroleum from some source other than the material that formed it. The duration leaves the geologist's inference untouched.
- DCorrect
Bacteria living deep in the crust provide a possible source of biological molecules in an existing petroleum deposit. Their presence needn't mean the petroleum itself formed from fossilized organisms. This gives us the alternative route we wanted: signs of life could reflect organisms living near or in the deposit rather than its original formation. It weakens the claimed refutation without proving the deep-carbon theory true.
- E
Some carbon deposits having a plant origin doesn't establish the origin of the particular deposits or petroleum at issue. It also doesn't show how the biomarkers got into this petroleum. The alternative theory concerns ancient deposits dating from the earth's formation; a fact about some plant-derived deposits doesn't resolve that explanation.
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