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By MARLAN DOWNEY

Overturning Theory Overturned

Perhaps a review -- and awareness -- of the past may make us better geologists in the future.

In 1955, the AAPG President's Award (now called the Robert H. Dott Sr. Memorial Award) was given to Paul V. Smith Jr., for his AAPG article titled "Studies on Origin of Petroleum: Occurrences of Hydrocarbons in Recent Sediments."

The editor of the Science newsletter cited Smith's study as one of the most significant science stories of the year. It pointed out that Smith's discovery of hydrocarbons deposited in recent sediments provided an important quantitative study by a chemist that overturned the general geologic opinion that oil was generated in the subsurface.

At least one major oil company spent many years trying to create a useful hypothesis of petroleum generation that could start with flushing sediment hydrocarbons into traps.

The measurements of hydrocarbons in recent sediments was correct, but ... further work demonstrated that these hydrocarbons were biomass and detritus of once-living organisms, and were not petroleum-like.

We now understand that petroleum hydrocarbons are the result of the transformation of organic matter under subsurface conditions of elevated pressure and temperature, often retaining fragments of the original organic molecules. The preserved fragments, called biomarkers, allow petroleum accumulations to be traced to a particular subsurface layer and to specific organisms abundant in that source layer.

We've come a long way in 50 years.