What is the moon of Saturn, Titan. Wasn't until around 2004 when we sent a Saturn fly by to investigate the atmosphere. It wasn't until then that we discovered that the majority of the atmosphere was made from hydrocarbon, as in methane. There are several other ways methane came be made. If like most Methane made we find here on Earth. If it is made, like we find it here, it was made from organic material.
Try reading this:
http://www.usnews.com/opinion/blogs/on-energy/2011/09/14/abiotic-oil-a-theory-worth-exploring
