Chemical evolution and the first life

Pasteur's result did not explain where the very first life came from. Oparin (Russia) and Haldane (England) proposed that it came from pre-existing non-living organic molecules such as RNA and protein.

Their key idea: life was preceded by chemical evolution, the making of diverse organic molecules from inorganic ingredients.

Conditions on early earth: high temperature, volcanic storms and a reducing atmosphere with CH₄, NH₃ and similar gases.

In 1953 S.L. Miller, an American scientist, recreated these conditions on a laboratory scale: electric discharge in a closed flask holding CH₄, H₂, NH₃ and water vapour at 800 °C. Amino acids formed.

Similar experiments by others gave sugars, nitrogen bases, pigments and fats. Meteorites carry similar compounds, suggesting the same chemistry happens elsewhere in space. On this limited evidence, chemical evolution is more or less accepted.

How the first self-replicating metabolic capsule arose is unknown. The first non-cellular life forms may have appeared about 3 billion years ago as giant molecules (RNA, protein, polysaccharides) that perhaps reproduced themselves.

Cellular life probably came much later, around 2000 million years ago, most likely as single cells; every life form then lived in water.

This account, in which the first life arose slowly from non-living molecules through evolutionary forces, is accepted by most scientists.