Episodes of intense volcanic eruptions in the distant past occurred in cycles having very long periodicities.
At the present time the global level of thunderstorm activity increases and decreases in cycles with periodicities of approximately 11 years.
In the distant past cyclical climatic changes had periodicities of longer than 200 years.
In the last century the length of the sunspot cycle has been known to vary by as much as 2 years from its average periodicity of 11 years.
Hundreds of millions of years ago, solar-activity cycles displayed the same periodicities as do present-day solar-activity cycles.
22. It can be inferred from the passage that Chinese observations of the Sun during the late seventeenth and early eighteenth centuries
are ambiguous because most sunspots cannot be seen with the naked eye
probably were made under the same weather conditions as those made in Europe
are more reliable than European observations made during this period
record some sunspot activity during this period
have been employed by scientists seeking to argue that a change in solar activity occurred during this period
23. It can be inferred from the passage that studies attempting to use tree-ring thickness to locate possible links between solar periodicity and terrestrial climate are based on which of the following assumptions?
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