Over the course of millions of years, the decayed organic matter that covered the earth was covered by soil and mud which eventually turned into rock. These layers of trapped organic matter changed composition into oil, coal, and bubbles of gas because of the heat and pressure from the weight above. Early man discovered places where natural gas escaping through fissures in the rock had been ignited by lightning, and hence discovered natural gas.
Wherever pools of oil have been discovered below the surface of the earth, there are usually pools of natural gas above, or below the pools in the shale rock formations. In the old days, these gas pockets were considered a nuisance because they hindered the easy pumping of the oil. It did not take too long before they figured out that gas had value as well.
Today, this odorless gas is harvested via pipelines to large gas processing plants where it is purified, and then distributed all over the country. Approximately 22% of our energy usage in the United States is natural gas. Natural gas powers many of our large electricity power plants, and is piped into homes in most cities for use in heating systems. More than 50% of American homes are heated by this once-considered nuisance. It is far more economical than heating oil, and cleaner than coal for heating uses.
While natural gas is essentially a non-renewable resource, there are now large machines called "digesters" that can manufacture natural gas from organic material It is not likely that large scale production could be achieved, but we do have the technology to produce it. The nasty odor associated with natural gas is an additive designed to warn us should there be a leak of this potentially dangerous gas. That rotten-egg smell is unmistakable, as well as intentional.
The article listed below as my source is quite interesting, and informative should you wish to know more about natural gas. It is one of our biggest natural resources, and important to our future!