The era featured the longest periods with no life forms on earth.

The answer is - Archean.
The Precambrian is the eon before the Cambrian, when the so called life explosion occurred. The Precambrian eon is the earliest part of Earth's history, set before the current Phanerozoic eon. This eon accounts for about 88% of the history of the Earth. It is consisted of three eras, Hadean (no life), Archean (no life), and Proterozoic (life occurred). Both of the two earliest eras do not have life, but Archean is three times longer period than the Hadean, so Archean is the answer.

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