Carbon (C) is a chemical element with atomic number 6. It's one of the most abundant elements on Earth.
Carbon is a necessary building block of all known lifeforms, everything from animals and plants to bacteria and fungus.
The carbon atom's four valence electrons (outer shell electrons) allows the atoms to arrange themselves and bond in various different ways, creating structures with very different attributes. These different structures are called allotropes. Two of the most well known carbon allotropes include diamond and graphite.
The most abundant carbon isotope is 12C (6 protons and 6 neutrons), but another well-known isotope is 14C (6 protons, 8 neutrons) whose radioactive properties and predictable half-life allows for accurate archeological dating ("radiocarbon dating"). Simply put, the less 14C found in a dead plant or animal, the longer ago it died.