GRE Reading Comprehension
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Source: 1997
Analysis of prehistoric air trapped in tiny bubbles beneath the polar ice sheets and of the composition of ice surrounding those bubbles suggests a correlation between carbon dioxide levels in the Earth's atmosphere and global temperature over the last 160,000 years. Estimates of global temperature at the time air in the bubbles was trapped rely on measuring the relative abundances of hydrogen and its heavier isotope, deuterium, in the ice surrounding the bubbles. When global temperatures are relatively low, water containing deuterium tends to condense and precipi- tate before reaching the poles; thus, ice deposited at the poles when the global temperature was cooler contained relatively less deuterium than ice deposited at warmer global temperatures. Estimates of global temperature based on this information, combined with analysis of the carbon dioxide content of air trapped in ice deep beneath the polar surface, suggest that during periods of postglacial warming carbon dioxide in the Earth's atmosphere increased by approximately 40 percent.
It can be inferred from the passage that during periods of post glacial warming, which of the following occurred?
- A The total volume of air trapped in bubbles beneath the polar ice sheets increased.
- B The amount of deuterium in ice deposited at the poles increased.
- C Carbon dioxide levels in the Earth atmosphere decreased.
- D The amount of hydrogen in the Earth's atmosphere decreased relatively the amount of deuterium
- E he rate at which ice was deposited at the poles increased