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Natural gas comes can be found in the underground, but its origin are the organic rests of a long time ago. However, my gas doesn't come from dead trees or anything like that. So what's an alternative source?

I'm thinking maybe the gas comes from underground pools of its liquid form, and evaporates when heated by an hotspot or an incoming volcanic eruption. But this poses the question of where the liquid comes from. Any ideas?

Thanks in advance.

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    $\begingroup$ Do you mean specifically methane gas or any gas? Liquid pools evaporating due to a hotspot are reminiscent of steam. Geysers and vents do exist naturally. $\endgroup$ – nzaman Aug 15 '18 at 7:17
  • $\begingroup$ No, not methane, a gas that doesn't exist in real life. And yes, I know, but wouldn't making this gas too similar to steam also cause it forming clouds and raining and everything? I don't want it to rain from the sky and form lakes, lol. $\endgroup$ – Virdex_ Aug 15 '18 at 7:47
  • $\begingroup$ And how, exactly, are you going to get these underground pools of its liquid form if it doesn't fall back? $\endgroup$ – nzaman Aug 15 '18 at 7:50
  • $\begingroup$ That's why I asked. And why I'm not sure the pools are a good idea. $\endgroup$ – Virdex_ Aug 15 '18 at 8:12
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    $\begingroup$ As a real-life example: Where do you think helium comes from? $\endgroup$ – Chronocidal Aug 15 '18 at 10:23
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  • Volcanic activity: various gases are releases as byproduct of volcanic activities. Think of CO2, H2O, H2S, SO2 for example.

  • Radioactive decay: other gases are produced as end or intermediate product of radioactive decay chains. An example of such gases is Radon.

About underground reservoirs: they can exist, but hardly in the liquid phase. It's simply too hot down there to keep a gas liquid.

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    $\begingroup$ Helium is also a decay product. $\endgroup$ – Ash Aug 15 '18 at 13:32
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  1. Your gas is incorporated into the planet during its formation and then gradually leaks out.

  2. Your gas is a thermal decomposition product of planetary core / mantle materials, or a product of radioactive decay of these materials.

There is a theory that natural gas is produced deep inside the earth from materials sequestered there during the formation of the planet: the abiotic theory of fossil fuels. Microbes get involved with fossil fuels secondarily because it is tasty for them, but they do not form it in the first place.

https://enviroliteracy.org/energy/fossil-fuels/abiotic-theory/

The abyssal, abiotic theory of oil formation continues to receive attention due to the work of retired Cornell astronomy professor Thomas Gold... Gold’s theory of oil formation, which he expounded in a book entitled The Deep Hot Biosphere, is that hydrogen and carbon, under high temperatures and pressures found in the mantle during the formation of the Earth, form hydrocarbon molecules which have gradually leaked up to the surface through cracks in rocks. The organic materials which are found in petroleum deposits are easily explained by the metabolism of bacteria which have been found in extreme environments similar to Earth’s mantle. These hyperthermophiles, or bacteria which thrive in extreme environments, have been found in hydrothermal vents, at the bottom of volcanoes, and in places where scientists formerly believed life was not possible.

Methane is definitely in space and definitely could have been part of the original constituents of Earth. I could imagine water might do this too - celestial space water is bound up with minerals and winds up deep in the earth as the planet condenses from a cloud of dust. Over time the water breaks loose and begins to migrate, ultimately escaping through volcanoes as steam.

  1. Gases formed as breakdown products do occur without biological involvement. @Ash notes helium for one. Radon gas gets attention because it is a health hazard. It is generated by radioactive decay of materials in the crust.
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