Final answer:
The subject in question is geologic time, specifically the Precambrian/Cambrian period.
Step-by-step explanation:
The subject in question is geologic time, specifically related to the Precambrian/Cambrian period. In geologic time, the divisions are organized in descending order: Eons, Eras, Periods, and Epochs. The Precambrian/Cambrian period falls under the Phanerozoic Eon, Paleozoic Era, Cambrian Period, and is the first period in the Paleozoic Era.