Here's why:

* Organic chemistry is the study of carbon-containing compounds, which is why carbon is the defining element of organic matter.

* Living organisms are made up of organic molecules, like carbohydrates, proteins, lipids, and nucleic acids. All of these molecules contain carbon.

* Fossil fuels (coal, oil, natural gas) are formed from the remains of ancient organic matter and are therefore carbon-rich.

While other elements are also present in organic matter, carbon is the one that defines it as organic.