Oil: fossil fuel or a con? The sceptical theory that won't die

Oil is a fossil, but the inorganic theory won't die

That crude oil comes from the decomposition of plankton, algae and ancient forests is a consensus few dispute in public. Until the energy bill bites and someone asks how much organic matter it took to fill the reservoirs that keep the world running.

The strongest answer lies in biomarkers: molecules of biological origin found in petroleum, verifiable with a sample and a lab. If crude were born from inorganic processes in the mantle, those signatures wouldn't exist. Those who defend the organic origin add a little-known detail: Earth spent millions of years covered in fern forests that no organism could decompose, piling up billions of tonnes of wood that pressure and continental drift turned into hydrocarbons.

The economics feed the doubt. For decades oil sat on land, cheap to extract. Today oil companies drill in ultra-deep waters with hugely expensive machinery. That contrast invites suspicion that the official story hides something. The abiogenic theory — oil without fossils, generated by deep geology — has no biomolecular answer, but it survives every time the price of a barrel or a litre of petrol climbs.

In the end, the controversy isn't settled with slogans. The biomarkers are still there, and science says oil is buried life. What nobody can quite explain is why, if it's a finite resource of biological origin, new oilfields keep turning up. There, neither the sceptics nor mainstream science close the file: the question of where hydrocarbons come from is also a question about the price we're willing to pay.