"Is mars soon to be around 25 million miles from earth in august? but in which direction does it come up at night? "
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Hydrogen in the Rock Column
PI: Freund, Friedemann
This proposal addresses the presence of hydrogen in the rock column. Hydrogen is an energy source for micro-organisms, especially for methanogens. The deep environment may have served as refuge for early Life in the aftermath of large impacts or during global glaciation episodes. Microbial communities in deep-seated rocks need an energy source and food. While it is well-known that hydrogen can be generated by the reduction of water through oxidation of transition metal cations, for instance Fe2+ in mafic and ultramafic rocks, a much more broadly distributed hydrogen source seems to exist in the top 20-30 km of the rock column.
This form of hydrogen is introduced through a solid state redox reaction taking place in the matrix of nominally anhydrous minerals that crystallized or recrystallized in water-laden magmatic or high-grade metamorphic environments. Those minerals invariably incorporate small amounts of water in form of hydroxyl, O3Si-OH. During cooling hydroxyl pairs undergo a redox reaction, in the course of which the protons “rip off” an electron from their oxygens. Two protons turn into hydrogen, while two oxygens change from valence 2- to 1- forming a peroxy link, O 3Si-OO-Si O 3. Molecular hydrogen is diffusively mobile and can enter the space between grains and dissolve in intergranular water films. It thus becomes accessible to micro-organisms.
We propose a study of the presence of hydrogen in rocks. We shall measure: (i) the slow release of hydrogen after crushing rocks in inert gas using a MIS-FET detector, sensitive over the 0.5-2000 vppm range with 5-10 sec resolution. We shall analyze rocks from mid- to lower-crustal and upper mantle environments; (ii) the near-instant release of hydrogen during fracture of single crystals using a fast mass spectrometer with micro-second time resolution. Combining the two types of measurements (i) and (ii) we expect to obtain information about the amount of hydrogen contained in the rock column and, hence, its availability to deep microbial communities.
This work is central to the Astrobiology Roadmap Goal 4, Objective 4.1 “Earth’s early biosphere’, to Goal 3, Objective 3.1 “Sources of prebiotic materials and catalysts”, and to Goal 2, Objective 2.1 “Mars exploration”. It will provide information about a source of molecular hydrogen that has never before been systematically investigated.
