FIG. 5.

Atmospheric gas-phase (i.e., for void spaces) and lithographic (i.e., for salt, or ice inclusions) pressure lapse rates for Mars. The atmospheric gas-phase pressure increases very slowly with increasing depth in the martian lithosphere and reaches 25 mbar at a depth of 13.8 km below the martian datum. In contrast, the lithographic pressure for salt or ice inclusions in the lithosphere can achieve 25 mbar at 19.5 cm of overburden depth. The lithographic pressure is entirely dependent upon the microbial niche being completely (i.e., 100%) sealed from outgassing; otherwise, the niche would equilibrate to the atmospheric pressure predicted by the gas-phase lapse rate.