PrepTest 137, Section 2, Question 11
Scientists examined diamonds that were formed on Earth(61 more words not shown)
The information above most strongly(6 more words not shown)
- AMost diamonds with(12 more words not shown)
- BUltraviolet light causes(10 more words not shown)
- CEarth's atmosphere contained(9 more words not shown)
- DSulfur-33 is rarely(13 more words not shown)
- EThe formation of(9 more words not shown)
Reading the argument
The unusual sulfur concentration tells us something about the atmosphere when these diamonds formed. We don't need to know the chemistry independently; the passage gives us the connections.
This higher-than-normal concentration requires particular chemical reactions, and those reactions require ultraviolet light. So enough ultraviolet light must have reached the surface to make them happen.
Now consider the oxygen. More than a trace would have blocked enough ultraviolet light to prevent those reactions. But we have the result that requires the reactions. That rules out an atmosphere with more than a trace of oxygen at the relevant time.
What we’re looking for
For the most-supported answer, I'd connect those facts and conclude that there was very little oxygen 2.9 billion years ago. Follow the evidence backward from the unusual diamonds to the conditions needed to produce their sulfur concentration.
Working the answers
- A
We know when these particular diamonds formed. We don't know when most diamonds with this unusual sulfur concentration formed. There could be many from another period. A takes information about the examined diamonds and turns it into a claim about the larger group.
- B
Oxygen's role here is blocking ultraviolet light from reaching the surface. The passage doesn't say oxygen reacts with sulfur-33, or even that oxygen participates in the chemical reactions producing the concentration. B combines familiar terms into a new chemical claim.
- CCorrect
More than a trace of oxygen would have prevented the ultraviolet-triggered reactions needed to explain these diamonds. Since the diamonds have the concentration those reactions explain, the atmosphere must have contained very little oxygen. ‘Very little, if any’ preserves the possibility of a trace; we don't have to conclude there was absolutely none.
- D
We don't know when oxygen became abundant. Suppose that happened only one billion years ago. Diamonds formed 2.4 billion years ago might then have formed under the same low-oxygen conditions as the examined diamonds. That is only an illustration, but it shows why we cannot infer that more recent diamonds rarely contain sulfur-33.
- E
The light requirement concerns the reactions that explain this unusually high sulfur-33 concentration. It isn't a requirement for forming any diamond whatsoever. Other diamonds could form without those reactions. E broadens a claim about a special feature into a claim about the entire process of diamond formation.
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