Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001

Abstract

Fresh fracture surfaces of the martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons (PAHs). These fresh fracture surfaces also display carbonate globules. Contamination studies suggest that the PAHs are indigenous to the meteorite. High-resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and Fe-sulfides. The carbonate globules are similar in texture and size to some terrestrial bacterially induced carbonate precipitates. Although inorganic formation is possible, formation of the globules by biogenic processes could explain many of the observed features, including the PAHs. The PAHs, the carbonate globules, and their associated secondary mineral phases and textures could thus be fossil remains of a past martian biota.

Precipitation of carbonates by Nesterenkonia halobia in liquid media

“…Carbonate precipitation has been studied both in vitro and in natural habitats and it has been suggested that this precipitation could be related to the formation of marine calcareous skeletons, carbonate sediments and deposits of carbonates in soils (Doetsch and Cook, 1973;Krumbein, 1979). Recently, the presence of carbonates in the cracks in a meteorite from Mars has created great controversy over the possible relationship of these carbonates to bacterial activity and the subsequent hypothesis of there existing or having existed life on the planet Mars (McKay et al, 1996). Di erent mechanisms of carbonate formation by bacteria have been described (Ehrlich, 1996).…”

Molecular indicators (biomarkers) of past life

“…Lunar samples contained no endogenous PAHs (Burlingame et al, 1971;Henderson et al, 1971;Holland et al, 1972). The report that PAHs and possible fossil microbial cells were found in a Martian meteorite collected in Antarctica, and the implications thereof concerning the origin of life, were intriguing (McKay et al, 1996). If the PAHs were not contaminants or artifacts, then the exciting hypothesis that life evolved during the early history of Mars had merit.…”

A multidimensional impact model for the discovery of extraterrestrial life

“…History shows that claims of non-communicative ET life were ambiguous for long periods of time. For example, the hypothesis of microfossils on the Martian meteorite ALH84001 (McKay et al 1996) have fueled controversies which still are discussed today (see e.g. Wainwright 2014).…”