Scientists examined diamonds that were formed on Earth about 2.9 billion years ago. These diamonds had a higher-than-normal concentration of sulfur-33. This concentration can be explained only by certain chemical reactions that are stimulated by ultraviolet light. If there had been more than a trace of oxygen in Earth's atmosphere 2.9 billion years ago, then not enough ultraviolet light would have reached Earth 's surface to stimulate the chemical reactions.

The information above most strongly supports which one of the following?

(A) Most diamonds with higher-than-normal concentrations of sulfur-33 were formed at least 2.9 billion years ago.
(B) Ultraviolet light causes the oxygen in Earth's atmosphere to react chemically with sulfur-33.
(C) Earth's atmosphere contained very little, if any, oxygen 2.9 billion years ago.
(D) Sulfur-33 is rarely found in diamonds that were formed more recently than 2.9 billion years ago.
(E) The formation of diamonds occurs only in the presence of ultraviolet light.

Source: LSAT
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1. Oxygen does not allow the UV rays to reach earth.
2. More UV rays, more stimulation and more sulfur-33.
3. So if more sulfur - 33 found in diamonds 2.9 billions years ago, this means more UV rays were reaching earth's surface.

This implies that less oxygen was present at that time. (C) is the correct answer.


(A) Most diamonds with higher-than-normal concentrations of sulfur-33 were formed at least 2.9 billion years ago.

(B) Ultraviolet light causes the oxygen in Earth's atmosphere to react chemically with sulfur-33.

(C) Earth's atmosphere contained very little, if any, oxygen 2.9 billion years ago.

(D) Sulfur-33 is rarely found in diamonds that were formed more recently than 2.9 billion years ago.

(E) The formation of diamonds occurs only in the presence of ultraviolet light.
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