Final answer:
There were at least 12 glaciation periods in the past 100,000 years, as part of the climatic patterns known as ice ages. The most recent ice age ended about 12,000 years ago after reaching its peak glaciation around eighteen thousand years ago.
Step-by-step explanation:
During the past 100,000 years, there have been multiple glaciation periods, which are part of larger climatic occurrences known as ice ages. Scientists have identified at least five significant periods of cooling, commonly referred to as ice ages, each of which included multiple glaciations. The most recent glaciation period began a little over 100,000 years ago and reached its peak around eighteen thousand years ago, with the last ice age ending about 12,000 years ago.
Regarding the number of glaciation periods in the last 100,000 years, the statement that there were at least a certain number suggests that the accurate option is the highest number that the periods could plausibly be. The given options are 4, 12, 20, and 60. Since scientists have documented repeated glacial cycles during the ice ages and the existence of more than one glaciation during these periods, the correct answer would be the highest number that we can infer from the information: (b) 12 glaciation periods.