Study of carbonate brioprecipitation on simulated planetary surfaces as a potential biosignature

Abstract

It has already been described that carbonates can be precipitated by prokaryotes by (i) altering their microenvironment with the addition or removal of ions and increase or decrease of pH; (ii) production of extracellular cell wall or organic compounds that capture or concentrate ions, as well as isolate the microenvironment from external variations; and (iii) passive deposition of the minerals in the organic compounds under the influence of environmental conditions. However, determining which were the depositions processes involved and whether the origin was abiotic or biotic in the geological record remains an uncertainty. During the Neoproterozoic, during the increase of O2 in the atmosphere, a great amount of carbonates were deposited around stromatoliths after the great ice ages. Therefore, it is possible to suppose that the increase of O2 could have assisted in its deposition, either by a physical-chemical change in the environment or by a change in the microcommunity of the stromatholiths. On Mars, based on the evidences of carbonates and liquid water, and on the theories of an ancient ocean and hydrothermal systems formed by impact, it is proposed that a hypothetical Martian microcommunity could present a different deposition of carbonates under an ancient Mars' radiation, atmosphere and substrate. In this project, the processes of establishment of microcommunities and formation of elemental, molecular and mineral biomarkers, through environmental simulations using samples from a modern hypersaline microbiome, will be studied. (AU)