CHON (or CHNOPS) is an mnemonic acronym for the four most common (or six most essential) elements in living organisms: carbon, hydrogen, oxygen, and nitrogen.
The acronym CHNOPS, which stands for carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur, represents the six most important chemical elements whose covalent combinations go to make up most biological molecules on Earth. Sulfur is used in the amino acids cysteine and methionine. Phosphorus is an essential element in the formation of phospholipids, a class of lipids that are a major component of all cell membranes as they can form lipid bilayers which keep ions, proteins and other molecules where they are needed for cell function and prevents them from diffusing into areas where they should not be, and are also an essential component of nucleic acids.
Carbonaceous asteroids are rich in CHON elements. These asteroids are the most common type and frequently collide with Earth as meteorites. Such collisions were especially common early in Earth's history and these impactors may have been crucial in the formation of the planet's oceans.