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
Each of the following, if true, would lend support to the
climatologists’ hypothesis EXCEPT:
(A) Earth did not pass through clouds of cosmic
dust earlier than 800,000 years ago.
(B) Two large asteroids collided 800,000 years ago,
producing a tremendous amount of dense
cosmic dust that continues to orbit the Sun.
(C) Earth’s average temperature drops slightly
shortly after volcanic eruptions spew large
amounts of dust into Earth’s atmosphere.
(D) Large bits of cosmic rock periodically enter
Earth’s atmosphere, raising large amounts of
dust from Earth’s surface.
(E) 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.