# Coal vs Oil

**URL:** <https://boards.straightdope.com/t/coal-vs-oil/289192>\
**Category:** Factual Questions\
**Created:** [February 9, 2005, 2:39pm UTC](https://boards.straightdope.com/t/coal-vs-oil/289192 "2005-02-09T14:39:05Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![The\_Flying\_Dutchman](https://avatars.discourse-cdn.com/v4/letter/t/9fc348/32.png) [@The\_Flying\_Dutchman](https://boards.straightdope.com/u/The_Flying_Dutchman)\
**Post date:** [February 9, 2005, 2:39pm UTC](https://boards.straightdope.com/t/coal-vs-oil/289192/1 "2005-02-09T14:39:05Z")

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Considering that both oil and coal originated from biological deposition, why is that over time some of this material turned to solid coal and some to liquid oil?

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**Author:** ![GorillaMan](https://avatars.discourse-cdn.com/v4/letter/g/50afbb/32.png) [@GorillaMan](https://boards.straightdope.com/u/GorillaMan)\
**Post date:** [February 9, 2005, 2:50pm UTC](https://boards.straightdope.com/t/coal-vs-oil/289192/2 "2005-02-09T14:50:01Z")

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IIRC, coal comes from plant matter, and oil from aquatic life (plankton etc.)

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**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\
**Post date:** [February 9, 2005, 2:54pm UTC](https://boards.straightdope.com/t/coal-vs-oil/289192/3 "2005-02-09T14:54:25Z")

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> [@grienspace](#):
>
> Considering that both oil and coal originated from biological deposition, why is that over time some of this material turned to solid coal and some to liquid oil?

Hmmm…about eight feet from me, there’s a bottle of cooking oil and a box of corn flour, both made from not only the same biological stuff but even the same species. Why is one liquid and one solid? (I say that not to be sarcastic, but to make the point that both content and processing are important in what results.)

We would probably have to get **Una Persson** or **Ringo** in here to go into the details, but essentially coal formed from the deposition of _ligneous_ organic matter where complex carbon-rich compounds were compressed and _reduced_ (in the chemical sense) to what we now consider coals. Look up lignite and its precursors to get a handle on some of the intermediate stages.

The production of crude oils is a bit more complex, but from what I gather essentially resulted from _reductive_ decay processes producing a wide array of hydrocarbons, the liquid constituents of which tended to concentrate where the combination of gravity (downward) and their specific gravity (floating above groundwater) brought them to rest. (The gaseous components, of course, separated out as natural gas, which is usually found above and in association with crude oil deposits.)

I get the distinct impression that the nature of the original materials played an important part in the results, too – and that the nature of the residual organic material typical for various periods of geologic time resulted in first one form of deposition and then the other.

I apologize for the vagueness of this – as noted, I don’t understand the specifics.