By examining atoms and molecules from non-living substances and examining equivalent atoms and molecules from living organisms. There are no differences between the atoms or molecules from different sources. The classic experiment was Wöhler’s synthesis of an organic compound, urea, from non-organic precursors in 1828.
The people who deny the possibility of abiogenesis are creationists and they are wrong. The study of abiogenesis is far from complete, but we have made progress and are continuing to make progress. See
New Glimpses of Life’s Puzzling Origins for more on the subject.
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