'A period is one of 4 major units of geologic time; these are the other 3, & they all start with "E"'
eon, era & epoch
PERIOD: A period is one of 4 major units of geologic time; these are the other 3, & they all start with E
A period is one of 4 major units of geologic time; these are the other 3, & they all start with "E"
A period is one of 4 major units of geologic time; these are the other 3, & they all start with "E"
PERIOD
eon, era & epoch
PERIOD