Preprints
https://doi.org/10.5194/egusphere-2022-1457
https://doi.org/10.5194/egusphere-2022-1457
23 Dec 2022
 | 23 Dec 2022

Biogenic calcium carbonate as evidence for life

Sara Ronca, Francesco Mura, Marco Brandano, Angela Cirigliano, Alessandro Grottoli, Massimo Reverberi, Daniele Federico Maras, Rodolfo Negri, Ernesto Di Mauro, and Teresa Rinaldi

Abstract. The history of Earth is a story of co-evolution of minerals and microbes: not only numerous rocks arisen from life, but the life itself may have formed from rocks. To understand the strong association between microbes and inorganic substrates, we investigated the moonmilk, a speleothem of calcium carbonate of microbial origin, present in the Iron Age Etruscan Necropolis of Tarquinia, in Italy. These tombs present a unique environment where the hypogeal walls of the tombs are covered by this speleothem. To study moonmilk formation, we investigated the bacterial community in the rock in which the tombs are carved: calcarenite and hybrid sandstone. We present the first evidence that moonmilk precipitation is driven by microbes within the rocks and not only on the rock surfaces. We also describe how the moonmilk produced within the rocks contributes to rock formation and evolution. The microbial communities of the calcarenite and hybrid sandstone displayed, at phylum level, the same microbial pattern of the moonmilk sampled from the walls of the hypogeal tombs, pointing out that the moonmilk originates from the metabolism of endolytic bacterial community. The calcite speleothem moonmilk is the only known carbonate speleothem on Earth with undoubted biogenic origin, thus representing a robust and credible biosignature of life. Its presence in the inner parts of rocks adds to its characteristics as a biosignature.

Sara Ronca et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1457', Anonymous Referee #1, 12 Feb 2023
    • AC1: 'Reply on RC1', Teresa Rinaldi, 09 Apr 2023
  • RC2: 'Comment on egusphere-2022-1457', Anonymous Referee #2, 20 Mar 2023
    • AC2: 'Reply on RC2', Teresa Rinaldi, 09 Apr 2023

Sara Ronca et al.

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Short summary
The history of Earth is a story of co-evolution of minerals and microbes. We present the evidence that moonmilk precipitation is driven by microorganisms within the rocks and not only on the rock surfaces. Moreover, the moonmilk produced within the rocks contributes to rock formation. The calcite speleothem moonmilk is the only known carbonate speleothem on Earth with undoubted biogenic origin, thus representing a biosignature of life.