PrepTest 44, Section 3, Question 17
Climatologists believe they know why Earth has undergone a regular sequence of ice ages beginning around 800,000 years ago. Calculations show that Earth's orbit around the Sun has fluctuations that coincide with the ice-age cycles. The climatologists hypothesize that when the fluctuations occur, Earth passes through clouds of cosmic dust that enters the atmosphere; the cosmic dust thereby dims the Sun, resulting in an ice age. They concede, however, that though cosmic dust clouds are common, the clouds would have to be particularly dense in order to have this effect.
Climatologists believe they know why Earth has undergone a regular sequence of ice ages beginning around 800,000 years ago. Calculations show that Earth's orbit around the Sun has fluctuations that coincide with the ice-age cycles. The climatologists hypothesize that when the fluctuations occur, Earth passes through clouds of cosmic dust that enters the atmosphere; the cosmic dust thereby dims the Sun, resulting in an ice age. They concede, however, that though cosmic dust clouds are common, the clouds would have to be particularly dense in order to have this effect.
Climatologists believe they know why Earth has undergone a regular sequence of ice ages beginning around 800,000 years ago. Calculations show that Earth's orbit around the Sun has fluctuations that coincide with the ice-age cycles. The climatologists hypothesize that when the fluctuations occur, Earth passes through clouds of cosmic dust that enters the atmosphere; the cosmic dust thereby dims the Sun, resulting in an ice age. They concede, however, that though cosmic dust clouds are common, the clouds would have to be particularly dense in order to have this effect.
Climatologists believe they know why Earth has undergone a regular sequence of ice ages beginning around 800,000 years ago. Calculations show that Earth's orbit around the Sun has fluctuations that coincide with the ice-age cycles. The climatologists hypothesize that when the fluctuations occur, Earth passes through clouds of cosmic dust that enters the atmosphere; the cosmic dust thereby dims the Sun, resulting in an ice age. They concede, however, that though cosmic dust clouds are common, the clouds would have to be particularly dense in order to have this effect.
Each of the following, if true, would lend support to the climatologists' hypothesis EXCEPT:
Earth did not pass through clouds of cosmic dust earlier than 800,000 years ago.
Two large asteroids collided 800,000 years ago, producing a tremendous amount of dense cosmic dust that continues to orbit the Sun.
Earth's average temperature drops slightly shortly after volcanic eruptions spew large amounts of dust into Earth's atmosphere.
Large bits of cosmic rock periodically enter Earth's atmosphere, raising large amounts of dust from Earth's surface.
Rare trace elements known to be prevalent in cosmic debris have been discovered in layers of sediment whose ages correspond very closely to the occurrence of ice ages.
Explanations
So some scientist's hypothesize that Earth's periodic passing through cosmic dust clouds caused our ice ages, specifically by dimming incoming sunlight.
Not the craziest idea, but certainly not proven by the argument.
It turns out to be a Strengthen Except question. The four wrong answers will increase the likelihood that Earth passing through these dust clouds caused the ice ages. The right answer will make it less likely, or won't affect the likelihood at all.
Let's see.
Nah, this strengthens. This improves the likelihood by syncing up the alleged timeline's starting point.
Nope. This strengthens. If this is true, then we have an explanation for how the cosmic dust came about on top of a corroborated starting timeline.
Nah, this strengthens, too. If this is true, then we have terrestrial examples of the alleged cooling phenomenon caused by cosmic dust. In other words, this is a microcosmic example of what's alleged to be happening on a global scale.
Yeah, this works. Even if this is true, this answer choice says nothing about the impact the kicked-up dust has on Earth's temperature. This is going to be the answer.
Nope. If this is true, then there's evidence that Earth passed through the cosmic dust along the hypothesized ice age timeline.
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