Dark microbiome and extremely low organics in Atacama fossil delta unveil Mars life detection limits

Abstract

Identifying unequivocal signs of life on Mars is one of the most important objectives for sending missions to the red planet. Here we report Red Stone, a 163-100 My alluvial fan–fan delta that formed under arid conditions in the Atacama Desert, rich in hematite and mudstones containing clays such as vermiculite and smectites, and therefore geologically analogous to Mars. We show that Red Stone samples display an important number of microorganisms with an unusual high rate of phylogenetic indeterminacy, what we refer to as “dark microbiome”, and a mix of biosignatures from extant and ancient microorganisms that can be barely detected with state-of-the-art laboratory equipment. Our analyses by testbed instruments that are on or will be sent to Mars unveil that although the mineralogy of Red Stone matches that detected by ground-based instruments on the red planet, similarly low levels of organics will be hard, if not impossible to detect in Martian rocks depending on the instrument and technique used. Our results stress the importance in returning samples to Earth for conclusively addressing whether life ever existed on Mars.

Exploring the Impact of Coconut Peat and Vermiculite on the Rhizosphere Microbiome of Pre-Basic Seed Potatoes under Soilless Cultivation Conditions

“…Investigations into phyllosilicate mineral, from which vermiculite originates, and materials with similar structures to vermiculite, indicate that surface microorganisms primarily belong to two groups: those involved in rock weathering and organotrophic microbes [ 22 ]. These microbial populations are generally low in abundance and often thermotolerant, with many exhibiting a mix of biological traits [ 23 , 24 ]. Yet, their ecological roles are still not fully understood.…”

Life on Mars, can we detect it?

“…The paper by Azua-Bustos et al 10 in Nature Communications describes analysis of samples collected from "Red Stone", an alluvial fan river delta more than 100 million years old in the Atacama Desert of Chile, Earth's oldest and driest desert. Red Stone has similar geology to the delta area currently being studied by NASA's Perseverance rover 11 (Fig.…”

“…SOLID was designed for life detection on Mars but no scheduled missions plan to use it. Interestingly, the LDChip detected evidence of cyanobacteria that were not seen in the modern microbiota so Azua-Bustos et al 10 posit these biosignatures were deposited along with the delta sediments at least 100 million years ago.…”

“…This Red Stone sample analysis 10 shows how critical it is to test instruments designed for life detection on other planets by using samples from relevant Earth analogs prior to selecting them for flight missions. If the biosignatures can't be detected in Earth samples, where both current and ancient life is clearly documented, we should not expect these instruments to be capable of detecting evidence of life from Mars' early history.…”

“…Azua-Bustos et al 10 argue that detection of ancient life signatures will require sample analysis in sophisticated laboratories. This same view has led to the current plans for searching for life: the Perseverance rover is collecting samples that are to be retrieved and brought to Earth by a future mission 14 .…”