Proceedings of the National Academy of Sciences of the United States of America

About the PNAS Member Editor
Name Thiemens, Mark H.
Location University of California, San Diego
Primary Field Geophysics
Secondary Field Chemistry
 Election Citation
Thiemens discovered and explored isotope anomalies in oxygen and sulfur not predicted by classical theory, which led to a deeper understanding of Earth's atmospheric composition and evolution. He developed new insights into atmosphere-surface interaction on Earth and Mars, and stimulated a new approach to theories of isotopic reaction mechanisms.
 Research Interests
My research is centered on our discovery and use of the mass independent fractionation process for stable isotopes and the concomitant applications. A portion of our work involves understanding the quantum level physical chemical mechanisms of the process. The specific nature of the isotopic partitioning process has provided a novel means by which transition state phenomena may be probed and quantified. We have applied measurements of these unique isotopic signatures to natural samples, both terrestrial and extraterrestrial. These studies include: The origin and evolution of the solar system from both meteorite measurements and molecular beam experiments as well as returned samples of the solar wind; definition of the source and transformation of greenhouse gases in the troposphere; chemistry of the stratosphere and mesosphere from rocket borne collections, especially the ozone cycle; the chemistry of the ancient Martian atmosphere; the origin and evolution of oxygen-ozone and life in the Earth's Precambrian; the history of sea water over million year time scales; and, the change of the oxidative capacity of the atmosphere from ice core sample collection and analysis from the Antarctic and Greenland. Paleo measurements have lead to new understanding of impacts of events upon the atmosphere and its chemistry over time, such as volcanoes and asteroidal impacts.

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