Eons are the broadest category of geologic time, and we live in the phanerozoic eon. the phanerozoic eon is further divided into eras. what divides the three eras of the phanerozoic eon?
a. mass extinction events separate the three eras from each other.
b. the first life on earth and the first multicellular life on earth separate the three eras from each other.
c. the development of insects and the development of flying insects separate the three eras from each other.
d. the appearance of carbon on earth and the appearance of atmospheric oxygen separate the three eras from each other.