by classifying into categories that get smaller and smaller these are the classification steps : life , domain , kingdom , phylum , class, order , family , genus , and species every time you narrow it down the option gets smaller and smaller till there's none left except the species it self .
"Carbon" is an element. It is found in the fourth group of the periodic table, and it is a stable element. This means that it can not be decomposed via heating, because if an element were to break down, it would release its subatomic particles. The explanation was probably one used to describe the thermal decomposition of a compound into smaller compounds.