Mass spectrometers on Viking, Phoenix, MSL, Mars2020 and the future ExoMars rover, for example, can detect organic molecules and the building blocks for life 7– 10. These spacecraft are equipped with various compositional instruments to identify minerals and look for raw molecules required for life. Liquid water is one of the main requirements, so many rovers have landed at sites with geomorphological evidence for ancient rivers and lakes and/or mineralogical evidence for liquid water, like clay minerals 4– 6. Landed missions like the Mars Exploration Rovers, Phoenix, and the active Mars Science Laboratory (MSL) and Mars2020 rovers were tasked with identifying habitable environments, and whether there are evidences for the requirements for life as we know it 2, 3. Past, current, and future missions to Mars are primarily motivated by the outstanding question of whether life ever existed on the red planet 1. Our results stress the importance in returning samples to Earth for conclusively addressing whether life ever existed on Mars. 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.

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.

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. Identifying unequivocal signs of life on Mars is one of the most important objectives for sending missions to the red planet.

Delta map fishing planet