After fierce bombardment of asteroids and comets on the ancient Earth, some 3.8 billion years ago, it is now being considered that the time window was ephemerally opened for the beggining of life. Everyone is stunned when one, at first, know the famous result of S.L.Miller's experiment of the prebiotic synthesis of building blocks for life to start chemical evolution.
But, Miller's experiment includes hydrogen gas as one of the main starting material. And many authors in the field say that the ancient atmosphere was not so hydrogen rich, but rather was neutral. In neutral condition, the Miller's experiment does not proceed with sufficient efficiency, nor the product chemicals can survive to eventually compose further complex molecules like RNA.
Can we still assume Miller's starting condition that the ancient atmosphere was reductive? What kind of proof is needed and can be found in the geological record to support Miller's condition?