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Comment by knuthsat | Hacker News Reader

I think it turned out that coal and oil are mostly heavily processed microorganisms. Trees never end up so deep.

You're thinking of oil. Coal is trees. https://en.wikipedia.org/wiki/Coal#Formation

Most existing coal was once trees, but large scale conversion of trees into coal was only possible in the carboniferous, when trees were new on the biological scene and there wasn't anything that could decompose them, so dead trees just piled up and slowly turned into coal under the anaerobic conditions of being buried under other trees.

You can still get coal made from trees, when a forest fire turns some wood into charcoal and that gets buried in the soil, or under unusual circumstances where a tree gets buried somewhere inhospitable to the microbes that can decompose lignin.

Interestingly, the Wikipedia article for coal formation links to this paper which refuted the idea that coal formation was primarily attributable to the delayed agility of microorganisms to break down lignin during the Carboniferous period: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4780611

I think it depends on the depositional environment, its still possible for trees to be buried before decomposition. Especially in forested areas with significant water flow. Once a log hits the muddy, anerobic bottom of a river/lake it essentially enters stasis, people fish centuries old logs out of rivers for profit.

All of these things happen at massive scales, so even though the vast majority of wood does decompose before it can be preserved, even a few percent is probably enough coal to power some future post nuclear apocalypse society's industrial revolution in a few dozen million years time.

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