The aim of this research is to determine how the volatile element content of the martian interior, surface and atmosphere changed over geological time. This aim will be achieved via cutting-edge sub-microscopic mineralogical analyses (via transmission electron microscopy (TEM)), as well as ambitious measurements of the hydrogen isotope content and abundance of water, chlorine and fluorine in hydrous phases within martian meteorites of differing ages (via secondary ion mass spectrometry (SIMS)). The results of this research will allow us to address important unanswered questions about the formation and evolution of Mars, such as:• How wet is Mars’ interior compared to the Earths, and how has this changed over time?• Is the martian mantle well mixed like Earths, or heterogeneous like that of the Earth’s moon?• Was there ever significant volatile cycling at the martian surface?Answering these questions will help determine how similar the Earth and Mars really are, hence this research has strong astrobiological implications.Through collaborations with researchers at the University of Hawaii and the Carnegie Institute (Washington D.C.) we will have access to a large suite of different martian meteorites, hence we will be able to produce an unprecedented amount of systematic data.The proposed mineralogical and chemical data will be cutting edge, as only a few laboratories worldwide have the instrumentation and expertise to perform these measurements. Dr. Hallis’ intimate knowledge of martian meteorite mineralogy and chemistry, extensive experience with SIMS hydrogen isotope measurement protocol and sample preparation, and advantageous collaborations make her uniquely positioned to carry out this research. Outstanding TEM capabilities, as well as the presence of a supportive and expanding planetary science group in the Earth and Planetary Sciences department (of which Prof. Lee is the Chair), makes Glasgow University the ideal place to base this fellowship.