At first glance, it is easy to see why one may disagree with my hypothesis that any matter that can burn in its solid or liquid state was once a living organism. After all, there are many substances that can burn and have never been part of a living organism, such as the inorganic compounds of magnesium, calcium and titanium, as well as hydrocarbons like naphthalene and paraffin.
However, upon closer examination, this retort fails to take into account the nature of these substances and how they relate to organisms.
It is true that substances such as the aforementioned inorganic compounds and hydrocarbons can burn without ever having been part of a living organism, however, these same substances were once parts of organisms in the distant past. For example, many inorganic compounds originally derive from minerals found within earth's crust which were originally formed from living organisms. Similarly, hydrocarbons are found in fossil fuels which come from the remains of long-dead organisms. Therefore, even though these substances may not have been part of a living organism recently, their current existence is still directly related to living organisms in the distant past.
Furthermore, while it is true that many materials can burn due to factors other than having been part of a living organism, such as the heat generated when striking a matchstick, the fact remains that a majority of materials that can be ignited require energy that originated from a living organism. For example, wood and other combustible materials contain energy stored within their molecules which was originally produced by photosynthesis within those organisms. Without this energy, these materials would be unable to burn and generate heat or light.
In conclusion, while there are certainly materials that can burn without having been part of a living organism recently, there is no denying that the majority of substances that can ignite have gotten their flammable energy from a once-living organism! How's that for a sick burn?