Self-study
Climatologists believe they know why Earth has undergone a regular sequence of ice ages beginning around 800,000 years ago. ████████████ ████ ████ ███████ █████ ██████ ███ ███ ███ ████████████ ████ ████████ ████ ███ ███████ ███████ ███ ██████████████ ███████████ ████ ████ ███ ████████████ ██████ █████ ██████ ███████ ██████ ██ ██████ ████ ████ ██████ ███ ███████████ ███ ██████ ████ ███████ ████ ███ ████ █████████ ██ ██ ███ ████ ████ ████████ ████████ ████ ██████ ██████ ████ ██████ ███ ███████ ███ ██████ █████ ████ ██ ██ ████████████ █████ ██ █████ ██ ████ ████ ███████
Summarize Argument: Phenomenon-Hypothesis
The author hypothesizes that the regular sequence of ice ages Earth has experienced since 800,000 years ago are caused by Earth’s passing through clouds of cosmic dust. According to this theory, the cosmic dust enters Earth’s atmosphere, which dims the sun, causing an ice age.
Notable Assumptions
The author assumes there’s no other explanation for what causes Earth’s regular sequence of ice ages. The author assumes that the occurrence of ice ages is correlated with Earth’s passage through clouds of cosmic dust.
17.
Each of the following, if █████ █████ ████ ███████ ██ ███ ███████████████ ██████████ ███████
a
Earth did not ████ ███████ ██████ ██ ██████ ████ ███████ ████ ███████ █████ ████
This strengthens by defending the argument from the possibility that passage through cosmic dust occcurred before the ice ages starting to occur.
Plausibility
Plausibility
Presenting evidence that corroborates (in Strengthen) or conflicts (in Weaken) with the author's hypothesized explanation or the predictions that follow from that explanation.
b
Two large asteroids ████████ ███████ █████ ████ █████████ █ ██████████ ██████ ██ █████ ██████ ████ ████ █████████ ██ █████ ███ ████
This helps establish that the dense cosmic dust the author’s hypothesis requires actually exists and correlates with the beginning of the ice ages.
Plausibility
Plausibility
Presenting evidence that corroborates (in Strengthen) or conflicts (in Weaken) with the author's hypothesized explanation or the predictions that follow from that explanation.
c
Earth's average temperature █████ ████████ ███████ █████ ████████ █████████ ████ █████ ███████ ██ ████ ████ ███████ ███████████
This strengthens by showing that dust in Earth’s atmosphere can reduce Earth’s average temperature. This makes the author’s theory about dust causing ice ages more plausible. Although (C) is about volcanic dust, it still shows that dust in atmosphere can cool the Earth.
Plausibility
Plausibility
Presenting evidence that corroborates (in Strengthen) or conflicts (in Weaken) with the author's hypothesized explanation or the predictions that follow from that explanation.
d
Large bits of ██████ ████ ████████████ █████ ███████ ███████████ ███████ █████ ███████ ██ ████ ████ ███████ ████████
(D) tells us that cosmic rock periodically enters the atmosphere. But does the Earth get colder after this happens? We don’t know. Do these periodic entries of cosmic rock coincide with Earth’s ice ages? We don’t know. (D) has no impact.
e
Rare trace elements █████ ██ ██ █████████ ██ ██████ ██████ ████ ████ ██████████ ██ ██████ ██ ████████ █████ ████ ██████████ ████ ███████ ██ ███ ██████████ ██ ███ █████
This provides evidence of a correlation between cosmic debris and the occurrence of ice ages.
Plausibility
Plausibility
Presenting evidence that corroborates (in Strengthen) or conflicts (in Weaken) with the author's hypothesized explanation or the predictions that follow from that explanation.