What other reasons are there to believe that abiogenesis preventing oxygen was in the Archean atmosphere?

Because water vapor will split into oxygen and hydrogen gases when exposed to ultraviolet light, it is reasonable to believe that the early atmosphere contained a sizable amount of oxygen. Volcanoes release water, carbon dioxide, and nitrogen.

The synthesis of DNA and RNA, which are essential for the replication of genetic information, is inhibited by oxygen.

(Canadian Journal of Earth Science 197 Environment of Archean Early Proterzoic Earth the Earth's Earliest Biosphere 1983) that Oxygen was present in the earliest atmosphere. Red rock strata indicating an Oxygen rich atmosphere occur in rocks thought to be older than 2 billion years old.

According to biochemical evidence, the earliest organisms had evolved an enzymatic defense mechanism against oxygen (Trends in Biological Sciences, 1995: Evolution of energetic metabolism, respiration, early hypothesis).

The main reason for believing that the early atmosphere lacked oxygen is the belief that abiogenesis occurred, though there are probably other reasons as well.

Several lines of evidence support the idea that abiogenesis likely occurred in an environment with little to no oxygen in the Archean atmosphere:

1. Geological Evidence: Rocks dating back to the Archean era contain chemical signatures suggesting low levels of atmospheric oxygen, such as the absence of oxidized minerals.

2. Chemical Reactions: Oxygen is reactive and can hinder the formation of complex organic molecules necessary for abiogenesis. A reducing atmosphere, low in oxygen, would have been more conducive to the synthesis of organic compounds.

3. Experimental Studies: Laboratory experiments simulating early Earth conditions have demonstrated that organic molecules can form under conditions lacking oxygen, supporting the hypothesis of abiogenesis in a reducing atmosphere.

4. Extant Anaerobic Life: Many organisms that thrive in environments devoid of oxygen, such as certain bacteria and archaea, provide modern examples of life that can exist and evolve in oxygen-poor conditions.

These factors collectively suggest that abiogenesis likely occurred in an environment where oxygen levels were minimal or absent.