Preprints
https://doi.org/10.5194/egusphere-2022-1457
https://doi.org/10.5194/egusphere-2022-1457
 
23 Dec 2022
23 Dec 2022
Status: this preprint is open for discussion.

Biogenic calcium carbonate as evidence for life

Sara Ronca1, Francesco Mura2, Marco Brandano1, Angela Cirigliano3, Alessandro Grottoli4, Massimo Reverberi5, Daniele Federico Maras6, Rodolfo Negri7, Ernesto Di Mauro3, and Teresa Rinaldi7 Sara Ronca et al.
  • 1Department of Earth Sciences, Sapienza University of Rome, Italy
  • 2CNIS-Center for Nanotechnology Applied to Industry of La Sapienza, 00185, Sapienza University of Rome, Rome, Italy
  • 3Istituto di Biologia e Patologia Molecolari, CNR, Rome, Italy
  • 4SARA EnviMob s.r.l., Rome, Italy
  • 5Department of Environmental Biology, Sapienza University of Rome, Rome, Italy
  • 6Soprintendenza Archeologia, Belle Arti e Paesaggio per la Provincia di Viterbo e l’Etruria Meridionale, Ministero della Cultura, Rome, Italy
  • 7Department of Biology and Biotechnology, Sapienza University of Rome, Rome, Italy

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: open (until 11 Feb 2023)

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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.