In the case of coal, we find the fossils of ancient ferns and trees in the coal itself.
In the case of oil, the sediments in which deposits are found, the fossils within those deposits, and the chemistry of the oil, all point to biotic rather than abiotic origin.
Yes, it's possible for hydrocarbons to form by other means. However there's vanishingly little physical evidence to suggest that that is what's actually happened.
Retrosplaining terrestrial hydrocarbon deposits based on remote observation, and one short-lived lander on an outer-solar-system moon (the Huygens probe on Titan, with very limited chemical sensig capabilities) in a hand-wavy attempt to invalidate several centuries of direct terrestrial experience with coal, oil, and gas geology is not exceptionally convincing.
In the case of oil, the sediments in which deposits are found, the fossils within those deposits, and the chemistry of the oil, all point to biotic rather than abiotic origin.
The paper I've linked in my earlier comment has far more detail and further references: https://news.ycombinator.com/item?id=28105383
Yes, it's possible for hydrocarbons to form by other means. However there's vanishingly little physical evidence to suggest that that is what's actually happened.
Retrosplaining terrestrial hydrocarbon deposits based on remote observation, and one short-lived lander on an outer-solar-system moon (the Huygens probe on Titan, with very limited chemical sensig capabilities) in a hand-wavy attempt to invalidate several centuries of direct terrestrial experience with coal, oil, and gas geology is not exceptionally convincing.