What sequence of events resulted for the pacific region having plants and animals that are different from those found from anywhere else?

I believe that the question refers to Australia and to the fact that it's been very isolated and that as a result it has developed a number of species which cannot be found anywhere else.
The series of events here would be 1. the geographical isolation of Australia. it separated from the other lands 99 million years ago and 2. the frequent  changes in climate it experienced which led to population bottlenecks, for example it was initially very warn and then it experienced a colder period.