CHON

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CHON is an mnemonic acronym for the four most common elements in living organisms: carbon, hydrogen, oxygen, and nitrogen. These four elements are also notable for being the least massive (and having the lowest atomic number) in their group in the periodic table.

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 meteorites may have been crucial in the formation of life on Earth.

Excluding noble gases, the CHON elements are the most common:

the main ingredients [of the primordial soup] are also some of the most abundant - Carbon (4th most abundant), Hydrogen (most abundant), Oxygen (3rd) and Nitrogen (6th) - CHON. (The other abundant elements, Helium and Neon, are both inert - they do not react with other elements)^[1]

CHON is featured in science fiction as the elements needed to sustain life in space colonies or as a lucrative space industry. In particular, CHON featured prominently in Frederik Pohl's Beyond the Blue Event Horizon which had an overpopulated Earth with 25 billion inhabitants. In this novel, a CHON "food factory" was discovered in the Oort cloud. This factory was mining carbonaceous asteroids which are high in CHON elements, and synthesizing edible food from them.

Sometimes the acronym CHONP is used to include the element phosphorus which is crucial in DNA and RNA.

Further, the acronym CHONPS may be used which is:

CHON (Carbon, hydrogen, oxygen and nitrogen) plus (SP: Sulfur, phosphorus) 99% of all living systems^[2]

Six of the 26 elements commonly found in living things.

Sulfur is used in the amino acids cysteine and methionine.