Figure 2: Comparison of gas compositions in Martian meteorites with those in terrestrial samples and carbonaceous chondrites.

The terrestrial samples are from basalts and terrestrial fluids. Each point corresponds to one burst of volatiles produced by an increment of crushing. Gases of interest are normalized to CO₂. All Martian meteorites plot within the data field for terrestrial basalts; both are more methane-rich than terrestrial fluids and carbonaceous chondrites. Errors are obtained from molar volumes of individual species±one weighted s.d. (see Methods). One Tagish Lake analysis has large error bar, but in most cases error bars are smaller than data symbols. Data sources: terrestrial serpentinites³⁹, and terrestrial basalts⁴⁵, both crushed in same manner as the meteorites.