Answer: The timeline in which life first evolved on Earth was the Archaen eon.
Life originated on earth in the early Archean eon, approximately 3.5 billion years ago.
The geological time scale depicts the sequence of events which took place on Earth. Eon occupies the largest unit in the geological timescale. There are four eons reported in the geological time. Archaen eon is the second eon on earth, dated 3.9 bya to 2.5 bya. It is also called as Archaeozoic Eon.
The most primitive form of life is prokaryote which appeared in the early Archean eon.