Oxygen is everywhere. Really, few elements are more abundant in the universe — in fact just two, hydrogen and helium. It combines with most other elements from the periodic table to form an incredibly wide range of compounds which serve an incredibly wide range of purposes. Just looking at the Earth: oxygen-bearing compounds are found in the mantle, crust, oceans and seas, atmosphere and living organisms, not to mention natural and man-made materials such as silica, zeolites, textiles, ceramics and drugs. Oh, and oxygen also takes part in energy production, as well as a variety of processes that range from metabolic to geological.
Oxygen is most frequently encountered in the form of isotope 16O, much more stable than 18O and 17O — this is because 16O boasts 8 protons and 8 neutrons, a ‘magic number’ in the atomic world that confers special stability. In this month’s ‘in your element’ article (subscription required), Mark Thiemens from the University of California, San Diego, explains how determining the ratio of oxygen isotopes has greatly contributed to our understanding of the evolution of natural processes and life on Earth. For example, the ratio of 18O to 16O is different in the atmosphere and in oceans (this is called the Dole effect). This difference arises from the photosynthesis and respiration of land-based or marine organisms, which means it can be used to deduce the evolution of terrestrial and marine activities.
Yet, the role of oxygen in the formation of the solar system remains unclear. Some meteorites that are known to be among the oldest objects in the solar systems have an unexpected oxygen isotopic distribution. Despite progress in the field, described by Thiemens in his article (they involve measurements on solar wind samples!), this distribution still remains unaccounted for, and exactly how the current celestial objects were formed remains unsolved for now.
Anne Pichon (Associate Editor, Nature Chemistry)