Page "Organic matter" Paragraph 18

Measurements of organic matter generally measure only organic compounds or carbon, and so are only an approximation of the level of once-living or decomposed matter.

Some definitions of organic matter likewise only consider " organic matter " to refer to only the carbon content, or organic compounds, and do not consider the origins or decomposition of the matter.

In this sense, not all organic compounds are created by living organisms, and living organisms do not only leave behind organic material.

A clam's shell, for example, while biotic, does not contain much organic carbon, so may not be considered organic matter in this sense.

Conversely, urea is one of many organic compounds that can be synthesized without any biological activity.