Periods of time are often divided into smaller units for easier measurement. The crossword solutions for the term 'periods of time' include ERAS (4 letters), days (4 letters), spans (5 letters), HOURS (5 letters), moons (5 letters), AGES (4 letters), EONS (4 letters), years (5 letters), and CENTURIES (9 letters). These terms refer to different lengths of time, ranging from the smallest unit of an hour to the longest unit of an eon.