Oparin and Haldane's theory and Miller's experiment are the proof that long complex molecules that carry information such as DNA, might have formed on early earth.
Explanation:
Oparin and Haldane Hypothesis states that life on Early earth could have evolved by chemical evolution.
Oparin and Haldane said that the reducing atmosphere of the early earth caused simple inorganic molecules to react by using sunlight and formed molecules like amino acids and nucleotides.
These monomers combined to form polymers, they would have attained self-replicating tendency eventually these would have assembled into structures and these macromolecules had also made membrane-bound organelle.
Although this hypothesis is not fully accepted but part of it which talks about formation of molecules is accepted.
Millers and Urey in their experiment created an artificial reducing environment like that of early earth. They used a heated pool of water, atmospheric gases like H2O,CH4,N2, NH4 and sparks of electricity. After running the experiment for some days they found that amino acids, sugars, lipids and other organic molecules had formed.
Their hypothesis is not fully accepted but part of is evident that organic building block is formed from inorganic constituent on the earth.
