SEM morphological studies of carbonates and the search for ancient life on Mars

Abstract

Next space missions will investigate the possibility of extinct or extant life on Mars. Studying the infrared spectral modifications, induced by thermal processing on different carbonate samples (recent shells and fossils of different ages), we developed a method able to discriminate biogenic carbonates from their abiogenic counterparts. The method has been successfully applied to microbialites, i.e. bio-induced carbonates deposits, and particularly to stromatolites, the laminated fabric of microbialites, some of which can be ascribed to among the oldest traces of biological activity known on Earth. These results are of valuable importance since such carbonates are linked to primitive living organisms that can be considered as good analogues for putative Martian life forms. Considering that the microstructures of biogenic carbonate are different from those of abiogenic origin, we investigated the micromorphology of shells, skeletal grains and microbialites at different scale with a scanning electron microscope. The results show that this line of research may provide an alternative and complementary approach to other techniques developed in the past by our group to distinguish biotic from abiotic carbonates. In this paper, we present some results that can be of valuable interest since they demonstrate the utility for a database of images concerning the structures and textures of relevant carbonate minerals. Such data may be useful for the analysis of Martian samples, coming from sample return missions or investigated by future in situ explorations, aimed to characterize the near-subsurface of Mars in search for past or present life.

Protection of the DNA from Selected Species of Five Kingdoms in Nature by Ba(II), Sr(II), and Ca(II) Silica–Carbonates: Implications about Biogenicity and Evolving from Prebiotic Chemistry to Biological Chemistry

“…Finally, in the presence of all DNAs, the biomorphs synthesized at a high CO 2 concentrations presented the biotic-type calcite and vaterite polymorphs, whereas the biomorphs in RTP conditions only presented the calcite polymorph (Table ). Among minerals, CaCO 3 is of great interest because organisms from all kingdoms are able to biomineralize it, generally in the calcite and aragonite polymorphs, and this finding is considered the most ancient evidence of life, although they can be synthesized biotically and abiotically. ,, The polymorph calcite (microbially induced) is a biogenic mineral that has been conserved in organisms for at least 500 million years and is present in most organisms. − Our results showed that the CaCO 3 biomorphs obtained in the presence of genomic DNA correspond precisely to the calcite polymorphism in all conditions (Table ). This is an important datum as it can explain the reason why this polymorphism in fossils is found in the five kingdoms in nature.…”

“…The process of crystalline mineral formation, like calcium minerals, has been considered to be a biomarker of the existence of life on Earth and other planets like Mars. − The crystalline minerals of Ca 2+ could display a biotic (microbially induced) or an abiotic origin as shown for Mars research in space. − Identifying the origin and polymorphs of calcium minerals is not a trivial effort because detection of biomolecular markers in crystalline minerals provides valuable information on the possible existence of life on Earth. In this sense, several authors have proposed that the minerals obtained from controlled mineralization processes can be used as biomarkers as they fulfill characteristics that are different from abiotic minerals with the same chemical composition .…”

Preservation of Organic Carbon in Dolomitized Cambrian Stromatolites and Implications for Microbial Biosignatures in Diagenetically Replaced Carbonate Rock

“…The lack of detailed insight into the preservation processes of organic matter, or biosignatures in general, within dolomitized carbonate lithologies is further complicated when applied to astrobiology. Carbonate lithologies are a recognized astrobiology target for Mars exploration (Cady et al, 2003;Summons et al, 2011;D'Elia et al, 2017). The primary science goal of the Mars 2020 mission is to determine whether life existed on Mars by seeking signs of extinct life in the rock record (Mustard et al, 2013;Williford et al, 2018).…”

Evaluation of CaSO4micrograins in the context of organic matter delivery: thermochemistry and atmospheric entry

“…In this context, the analysis of a peculiar class of materials, that we may call ‘white soft minerals’ (WSM) including calcite, magnesite, gypsum, talc, might represent a key point in panspermia theory, as these materials are often associated with the presence of organic matter (Gooding et al 1988; Pizzarello et al 2006; Orofino et al 2009; Yabuta et al 2014; D'Elia et al 2017).…”