Is the Mesozoic Era the longest?

The answer is NOOOO!!!! It is not the longest Era!!! The Precambrian consisted of the Archean and Proterozoic Eras which each pull roughly 2 billion years of geologic time making up the first 4 billion years of Earth. The Archean from 4.5 Billion Years Ago to about 2.5 BYA and the Proterozoic from 2.5 BYA to about 570 MYA. The Paleozoic which preceded the Mesozoic lasted about 345 Million years (570 MYA- 225 MYA) and the Mesozoic lasted about 215 Million years (225 MYA- 65 MYA).