Is petroleum, also known as oil, a fossil fuel, or is it abiotic or “abiogenic” in origin?
Even before articles about this question started hitting the Internet in force back in 2008, the thought occurred to me that oil may not truly be a fossil fuel. What led me to this surmise were 2 considerations. First, a very large amount of oil, whether measured in tons or barrels, has already been recovered from both the land and beneath the ocean floor. And, by all estimates, there is still much that can be recovered from the land and offshore throughout the world (including around the often overlooked continent, Antarctica). The total mass of the oil that has been recovered so far would seem to be well in excess of the mass of all the dinosaurs and other fossilized animal life that we postulate that oil is fermented (or whatever the actual process is that we are assuming when we refer to oil as a “fossil” fuel) from. Of course, who can guess what the mass of all the fossilized animal remains in the past few hundred millions of years totals to? This leads to the second consideration.
Secondly, consider from where petroleum has been recovered. So much has been recovered in the Middle East onshore. This area is now a desert, but hundreds of millions of years ago the so-called Tethys Sea existed at this spot on the globe. This sea closed after Pangea broke apart and the continents began moving towards their modern (current) locations. So, it is a mystery where all that subsurface oil in the Middle East came from. Was it from marine life that died in the Tethys Sea and then, after falling to the bottom, somehow fossilized and remained in sea floor sediments to be upthrust later when land occupied the area of the former sea? Not much large sea life has a chance to fossilize as fish eat other fish. (Okay, here, I may have tripped myself up. After posting this last evening, it occurred to me that the land under which this oil is located migrated to its current location on the globe from a different location due to plate tectonics. So, this oil may have been from land based animal life, if oil one accepts that oil is truly a fossil fuel. Yet, it is still puzzling as to how so much oil could be concentrated in such a small portion of the land surface area of the earth.)
How about the current large oil prospects offshore of Brasil (now the world’s fifth largest economy), being explored and developed by Petrobras?
Here let me cite an online article, emphasis (bold font) mine (with proper source credit given after quote):
Some of the largest oil finds in more than two decades were discovered recently off the coasts of Rio de Janeiro and Sao Paulo, potentially holding as much as 100 billion barrels of crude. But they are located in one of the most hostile and inaccessible environments on earth, lying deep under the Atlantic Ocean seabed beneath a thick layer of salt. http://gcaptain.com/brazil-pushes-innovation-offshore/
Again, a mystery! That large a volume of oil buried deep under the ocean floor. How does a liquid supposedly from the fossilized remains of animal life get to such a location given plate tectonics (continental drift), and the fact that the fossilization process of large marine animal life is not very efficient in ocean waters?
Perhaps, all we can safely say is that we really do not know for sure how oil is produced, or, alternatively, where it comes from. It may be that various processes, within the earth’s continental and seafloor crust, make oil and that it is abiotic in origin and nature.
Now, as for coal – that I can believe is a fossil fuel from the fossilized remains of forests. The various peat marshes in the world provide support to the idea that coal is truly a fossil fuel.