Here's why:

* Essential Building Block: Carbon is the backbone of all organic molecules, which are the fundamental building blocks of life. This includes carbohydrates, lipids (fats), proteins, and nucleic acids (DNA and RNA).

* Ubiquitous: Carbon is found in every single living organism, from the smallest bacteria to the largest whales.

* Solid at Room Temperature: Carbon exists as a solid in its elemental form (graphite, diamond) at room temperature.

While carbon can exist in other forms (like carbon dioxide), it is the solid form that is found within living organisms.