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. the appearance of carbon on earth and the appearance of atmospheric oxygen separate the three eras from each other.
b. the development of insects and the development of flying insects separate the three eras from each other.
c. the first life on earth and the first multicellular life on earth separate the three eras from each other.
d. mass extinction events separate the three eras from each other.

D. Mass extinction events separate the three eras from each other

Explanation:

The Phanerozoic represents an eon, and it is the most recent one. It is further divided into three eras, Paleozoic, Mesozoic, and Cenozoic. The division between the tree eras is because of mass extinction events. The Paleozoic and Mesozoic era are divided by the Permian-Triassic mass extinctions. The Mesozoic and Cenozoic are divided by the Cretaceous-Paleogene extinction. The Cenozoic era is still in existence, as there hasn't been a mass extinction of a magnitude big enough so far.

on island x the species needed to adapt because they were being subject to predators which didn't inhabit island y.