Self-study
When polar ice caps grow (during ice ages, for example), lighter forms of oxygen from water vapor and seawater accumulate in the frozen ice caps, leaving greater concentrations of one heavy form of oxygen behind in the sea, where it is absorbed by marine organisms. ████ ███ ██ ███ ███ ████ ███████ ███ ██████████████ ██ ████ █████ ██████ ██ ████████ █████████ ██████ ███ ███████████ ███████ ██████████████ ██ ████ █████ ██████ ██ ███ █████████ █████████ ███ █████ ██████ ██████ ████ █████████ ███ ██████ ██████
Summary
When polar ice gaps grow, greater concentrations of a heavy oxygen form are left in the ocean, which gets absorbed by marine life. When polar ice caps shrink, lower concentrations of this heavy oxygen are left in the ocean. So, we can predict whether ice caps were growing or shrinking by examining the concentrations of heavy oxygen in sea life during a time period. During one 30,000 year period, concentrations of heavy oxygen increased during the first 20,000 years, then decreased in the remaining 10,000 years.
Strongly Supported Conclusions
Polar ice caps were growing during the first 20,000 years of that period, then shrinking during the last 10,000 years.
14.
The information given most strongly ████████ █████ ███ ██ ███ █████████ ██████████ █████ ███ ██████ █████████ ██████
a
Average global temperatures ██████ █████ █████ ███ █████████ ██ ███ ██████ █████████████ ███████ ███████ ██████ ████████████ ██████ █████ ██████
Unsupported, because the stimulus doesn’t give us evidence concerning average global temperature. Even if you think ice caps are evidence of global temperature, the stimulus would suggest global temperatures shrank over the first 20,000 years, because the ice caps were growing.
b
Polar ice caps ██ ███ █████████ ██ ███ ██████ ████ ██████ ████ ████ ████ ██ ███ ███ ██ ███ ███████
Unsupported, because we don’t know the rate of growth or shrinkage. Ice caps grew for 20k years, then shrank for 10k years. But they could have grown much more than they shrank. This would mean the ice caps were larger at the end of the period.
c
The beginning of ███ ██████ █████████ ████ ███ █████ ██ ██ ███ ███ ████ ██████ █████████████ ██████ ██████
Unsupported, because we don’t have reason to think that the period began at the “onset” of an ice age. An ice age could have been in effect for much longer, and the 30k period just begins in the final 20k years of an ongoing ice age.
d
The polar ice ████ ████ ███ █████ ██████ █████ █████ ███ ██████ ██████ ████ █████ ██ ███████
Strongly supported, because concentrations of heavy oxygen grew for 20k years, then decreased for 10k years. This is evidence the ice caps grew during the first 20k years, then shrank in the next 10k years.
e
An ice age ███ ███████ ██ ██ ███ ██████ ███ █████ ██████ █████ ██ ███ ███████
Unsupported, because an ice age might have started at the beginning of the period and ended in 20k years. There’s no evidence that the 30k period began just as an existing ice age was ending.