The time gap between the formation of the Earth and the origin of life is approximately .......

Two statements regarding the origin of life are given below:
$(a)$ The first organisms that emerged on Earth are believed to have been devoid of chlorophyll and incapable of respiration.
$(b)$ The first food-producing organisms were chemosynthetic and never released oxygen.
Based on the above statements,which of the following options is correct?

Assertion: The primitive atmosphere was a reducing one,i.e.,without oxygen.
Reason: In the primitive atmosphere,oxygen was involved in forming ozone.

Stanley Miller observed the synthesis of ........ during his experiment.

Who proved that life comes from pre-existing life?

The first organisms to evolve on Earth were-