What is the evidnce for it. Is it just a theory or is there concrete proof that the billions of gallons of Petroleum that we have been pumping out of the earth is just rotten pre historic plankton and sea creatures.
Are there any other theories that have been proposed.
I think this is broadly accepted. Perhaps all fossil fuels are interconnected in how they are deposited. it’s clear that coal has a fossil origin because coal itself often is clearly recognizable as fossils such as the shapes of plants.
But there is a variant theory out there that petroleum also has a different origin, I think from the beginnings of the Earth itself. Maybe the primordial debris around the Sun contained organic molecules or something like that. I think the theory has enough fans that big oil companies sometimes spend serious money looking into it. I think the significance of it is that maybe they should be exploring for oil in places that nobody thinks have ancient deposits of living material.
One way is by looking at the rhenium and osmium concentrations similar to how they use carbon-14 dating for dating in archaeology.
But to be clear they are not actually from Fossils or the mineralized remains of old plants, that is just a misnomer.
There is an abiogenic theory of petroleum formation (or rather, two such).
They’re generally considered bunk.
Follow the money. AIUI, one of the strongest bits of evidence for favoring the biogenic hypothesis of petroleum origins vs. abiogenic hypotheses is how successful they are at predicting where oil should be found. Using the biogenic hypothesis for predicting which geological formations should contain oil gives good (albeit not infallible) results - oil companies, overall, make money buying mineral rights and sinking pilot wells based on such predictions. Predictions based on abiogenic hypotheses pretty much always lead to dry wells - oil companies, overall, lose money trying to use such predictions.
gdave nails it. The biogenic theory provides us with a predictive science. It makes useful and validatable predictions. To expand a little. If you are looking for oil or gas you will start by looking for provinces with histories that suggest there were good biological sources present in the past, and which would have been around at a time where later geological processes would have buried them. Modelling things like sedimentary processes can sometimes help understand what is buried and where.
That is a very broad start. Various surveys of the area would be looking for features that could trap any resulting fluids. Understanding the broad geological features and history. But a critical part of this is to model the thermal history of the province. You need to cook the biomass just right. In particular if it is overcooked you get coal. (Coal is everywhere, but mostly useless, as it won’t flow up a pipe.) These basic guides can tell you if it is worth spending the big money on seismic and exploratory drilling.
So - somewhere where there was biomass on the surface, subsequently buried, proper thermal history. Find these, and you have good reason to commit the many millions needed in the next phase of exploration. And it works.
The early earth had CO2 and water vapor for atmosphere. There was no oxygen.
It was biological life than converted all that CO2 to Oxygen (to about 30+% which later decreased to the current levels).
Where did all the C from all the CO2 go ? I think petroleum is one of the places.
Good episode of Skeptoid on the facts and fallacies of abiotic oil.
Basically a load of conspiracy theory riddled pseudo-science