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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.
In the passage, the author is primarily concerned with doing which of the following?
A.Describing a new method of estimating decreases in global temperature that have occurred over the last 160,000 years
B.Describing a method of analysis that provides information regarding the relation between the carbon dioxide content of the Earth's atmosphere and global temperature
C.Presenting information that suggests that global temperature has increased over the last 160,000 years.
D.Describing the kinds of information that can be gleaned from a careful analysis of the contents of sheets
E.Demonstrating the difficulty of arriving at a firm conclusion regarding how increases in the amount of carbon dioxide in the Earth's atmosphere affect global temperature
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
The author states that there is evidence to support which of the following assertions?
A.Estimates of global temperature that rely on measurements of deuterium in ice deposited at the poles are more reliable than those based on the amount of carbon dioxide c.ontained in air bubbles beneath the polar surface
B.The amount of deuterium in the Earth's atmosphere tends to increase as global temperature decreases.
C.Periods of post glacial warming are characterized by the presence of increased levels of carbon dioxide in the Earth's atmosphere.
D.Increases in global temperature over the last 160,000 years are largely the result of increases in the ratio of deuterium to hydrogen in the Earth's atmosphere.
E.Increases in global temperature over the last 160,000 years have been accompanied by decreases in the amount of deuterium in the ice deposited at the poles.
It can be inferred from the passage that the conclusion stated in the last sentence would need to be reevaluated if scientists discovered that which of the following were true?
A.The amount of deuterium in ice deposited on the polar surface is significantly greater than the amount of deuterium in ice located deep beneath the polar surface.
B.Both the air bubbles trapped deep beneath the polar surface and the ice surrounding them contain relatively low levels of deuterium.
C.Air bubbles trapped deep beneath the polar surface and containing relatively high levels of carbon dioxide are surrounded by ice that contained relatively low levels of deuterium.
D.The current level of carbon dioxide in the Earth's atmosphere exceeds the level of carbon dioxide in the prehistoric air trapped beneath the polar surface.
E.Increases in the level of carbon dioxide in the Earth's atmosphere are accompanied by increases in the amount of deuterium in the ice deposited at the poles.
