Subject: Why do many hold that the early atmosphere was reducing without oxygen

Quoting from Molecular Earth Sciences and the Origin of Life:"The atmosphere must 
have lacked oxygen because, for one thing,"laboratory experiments show that 
chemical evolution...would be largely inhibited by oxygen" and because 
compounds such as amino acids "are not stable over geological times in the 
presence of oxygen." There is no assurance that it was reducing. 

Re: Why do many hold that the early atmosphere was reducing without oxygen