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(STFC DTP) The atmospheric evolution of Mars

Project Description

Mars atmospheric evolution was marked by an early, dense CO2-rich atmosphere giving sufficient greenhouse warming to enable liquid water at the surface; followed by atmospheric loss leaving a less dense atmosphere with cold, arid surface conditions. The timing of atmosphere loss is not known, but may have coincided with a period of heavy meteorite bombardment at ~3.9 Ga. Noble gases offer key insight into the processes controlling the atmosphere systems on terrestrial planets. Because they are inert, the behaviour of noble gases in planetary reservoirs is controlled by relatively simple physical processes. As volatile elements, they are strongly depleted leading to significant modification of their primary isotope ratios (i.e. acquired at the time of accretion) by radioactive decay of isotopes of other elements. Where this occurs, the range of half lives provided by the precursors 129I (decaying to 129Xe in 16 Ma), 244Pu fission (131-136Xe, 80 Ma), 40K (40Ar, 1.3 Ga), 238U fission (131-136Xe, 4.5 Ga) provide distinct time constraints on models of atmosphere evolution.
Martian meteorites are our only samples from Mars, and are mostly relatively young (≤1.3 Ga) igneous rocks that are considered to be largely unrepresentative of the martian surface. However, in 2013, the first martian meteorite identified as a regolith breccia from the martian surface was described. As a breccia, this meteorite contains a diverse array of lithic components that crystallised by ~4.4 Ga punctuated by impact-driven resetting events all the way to 170 Ma. Martian atmospheric gases trapped within different lithic clast components could potentially provide a unique record of the early martian atmosphere.
The aim of this project is to determine the noble gas isotopic composition of the martian atmosphere through time. A major focus will be on noble gases in clast components of the matain regolith breccia meteorite North West Africa (NWA) 8114. A clast-by-clast approach will be used in an attempt to piece together the evolution of the martian atmsophere over time. If ancient and modern noble gas components in NWA 8114 can be resolved it will provide insight into: the source of accretionary volatiles (e.g. solar, cometary), the timing and extent of atmospheric loss; and the rate of atmospheric replenishment by degassing of the martian mantle. To provide context and additional insights, results from NWA 8114 will be supported by analyses of other selected martian meteorites, including the younger shergottites which retain a noble gas signature representative of the modern atmosphere, and nahklites which show evidence for a more ancient atmospheric noble gas composition.
Samples will be characterised using optical and electron microscopy techniques, and mineral chemistry by electron microprobe. Noble gas isotopes will be analysed in individual components (clasts, mineral separates, shock glass) using noble gas mass spectrometry.

The project would suit a student interested in planetary evolution, Mars science and geochemistry. This is a laboratory-focussed project so good practical skills and a willingness to learn and apply analytical techniques is essential. A background in geoscience, physics or chemistry at undergraduate level is desirable.


Agee C. B., et al. (2013) Science, 339, 780–785.
Cartwright J.A. et al (2014) Earth and Planetary Science Letters 400, 77-87
MacArthur J.L. et al (2019) Geochimica Cosmochimica Acta 246, 267-298.
Ott U. et al (2019) Volatiles in the Martian Crust, Chapter 3, 35-70.

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