Mark Howard Thiemens is a distinguished professor and the John Doves Isaacs Endowed Chair in Natural Philosophy of Physical Sciences in the department of chemistry and biochemistry at the University of California San Diego. He is best known for the discovery of a new physical chemical phenomena termed the mass independent isotope effect.
His studies have crossed a broad range of topics including basic physical and quantum chemistry, Solar System origin, tracking the origin and evolution of life on early Earth; stratospheric chemistry, climate change and greenhouse gas identification, Mars atmospheric chemistry, past and future and isotope geochemistry. His work combines photochemical isotope studies, both laboratory and synchrotron based, field work in the South Pole, Greenland Summit and the Tibetan Himalayas for climate and geological sampling across China for early Earth rock records.
His non-isotope work has included discovery of an unknown source of the greenhouse gas nitrous oxide that lead the global industrial elimination of all emissions, a major contribution to changing global climate change. Thiemens has worked on developing new imaging techniques for space mission return samples and detection of superconductivity in nature.