Which one of the following gases was not present in free form at the time life originated on Earth?

The theory of spontaneous generation states that:

Stanley Miller simulated the conditions of pre-biotic Earth using a spark-discharge apparatus. Which organic compounds were observed by him upon analyzing the end product of his experiment?

An evolutionary explanation of the origin of plants and animals was given by

Give scientific reasons: Life originated from the Earth's inorganic atmosphere in the past,but this no longer happens today.

Define/Explain: Proteinoids.