What’s the justification for the answer being “immutable” vs. “turbulent”? Immutable = unchangeable…where is the evidence?
The phrase “At long enough timescales” suggests a consideration of change or lack thereof over extended periods. Then, the information about the Earth experiencing “at least five ice ages in its 4.5-billion-year lifespan” demonstrates a history of substantial change.
So, the hint towards the word “immutable” comes from the juxtaposition of the concept of long timescales with the historical data that evidences notable changes (ice ages), implying that the Earth has not been unchanging or “static” over those timescales.
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turbulent - This word can mean characterized by conflict, disorder, or confusion, and in a geological or meteorological context, it might describe chaotic or unstable conditions. It could potentially fit in the blank, but let’s check the other options.
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immutable - This means unchanging over time or unable to be changed. This option fits as the opposite of what the sentence is describing (numerous ice ages, indicating change) and is therefore a likely fit for the blank.