Life is sometimes thought of as 'carbon chemistry', but around 25 components are essential for life. It is normal to divide these into trace elements and major elements according to their concentration. Table shows components classified in this way and according to their diverse roles. Nearly all known elements may be detected in the human body by modern analytical methods, but most are presumed to be there adventitiously without playing a vital role. To connect whether an element is essential is therefore difficult, especially as some essential elements are present in much lower concentrations than many adventitious ones such as Sr or Rb.
Most major components of life (except P) are readily available in sea water, which can resemble the environment in which life start. They filled three main functions. Nonmetallic components (except Cl) are components of covalently bound molecules and ions. H, N, C, O and usually S are constituents of proteins, and nucleic acids (RNA and DNA) have P as well. The chemical forms of those components differ.