From, “Studies on Origin of Petroleum; Occurrence of Hydrocarbons in Recent Sediments,” by P.V. Smith, Esso, “…It seems plausible to suggest that petroleum is being formed in the present era and that the crude product is nature’s composite of the hydrocarbon remains of many forms of marine life.”
This was a very thorough piece of work, documenting that hydrocarbon molecules from recently living cells are abundantly dispersed in many muddy sediments.
Analytical techniques of the time suggested a similarity between these hydrocarbons and crude oils. Many geologists and geochemists seized on this work to pronounce that the problem of the origin of petroleum had been solved, and the only remaining questions involved collection and migration of these recent hydrocarbons to traps.