Redox regulation of atmospheric oxygen and its consequences

Abstract

MANY attempts^1–9 have been made to explain why the concentration of atmospheric oxygen remains steady at ∼21%. I previously suggested that the turnover of marine and brackish water sediments promotes a recurrent demand for dissolved oxygen by alternately oxidising and reducing insoluble inorganic iron. Oxygen incorporated with sediments by this means combines with hydrogen to form water—thus preventing to some extent that loss of hydrogen by which Earth is oxidised^4,7. It is now apparent that regulation of molecular oxygen cannot be brought about by iron alone because the rate of turnover (even of shallow water sediments) is not fast enough¹³. Nor can sulphur (on its own or in association with iron) effect the transfer of sufficient oxygen from the aerobic to the anaerobic environment if rates of microbial activity in deep sea sediments are generally 1–2 orders of magnitude slower than in those of the continental shelves^12,15 propose, therefore, that six elements (N, Mn, Fe, S, C, H) circulate in reduced and oxidised forms between the aerobic and anaerobic environments and bring about ‘redox regulation of atmospheric oxygen’.