Mineralized biosignatures in ALH-77005 Shergottite - Clues to Martian Life

Abstract

The ALH-77005 Martian meteorite was found in Allan Hills on Antarctica during the Japanese National Institute of Polar Research (1977-1978) mission. One thin section sample was studied by optical microscopy for microtexture and by FTIR-ATR microscopy for interpretation of biogenic minerals and embedded organic materials. The geochemical data (biogenic elements, δ 13 C) of ALH-77005 meteorite from literature implementing recent results were compared to terrestrial geological samples. The ALH-77005 has poikilitic textures with coarse pyroxenes and brown olivines, and with recrystallized melt pocket. The coarse-grained minerals do not contain any alteration along the grain boundaries. Melt pocket and vicinity of opaque minerals contain biogenic signatures as filamentous, coccoidal forms of iron-oxidizing bacteria. The biosignatures were determined by 1) coccoidal, filamentous forms, 2) presence of embedded organic material, 3) presence of biogenic minerals, like ferrihydrite, goethite, and hematite. The other signatures for biogenicity of this meteorite are strong negative δ 13 C, enrichment of Fe, Mn, P, Zn in shock melt support scenario. This study proposes presence of microbial mediation on Mars.