[Microbial geochemical calcium cycle].

Area of Science:

• Geochemistry
• Microbiology
• Biogeochemical Cycles

Background:

• Microbial participation is key to the geochemical calcium cycle, influencing inorganic carbon fate and atmospheric CO2 removal.
• Early calcium deposits formed when prokaryotic life dominated; later, biogenic deposition by skeletal organisms became crucial.
• While most prokaryotes contribute universally, some, like cyanobacteria, play specialized roles in calcium cycling.

Purpose of the Study:

• To elucidate the critical role of microbial communities in the geochemical calcium cycle.
• To understand the mechanisms of calcium carbonate deposition mediated by prokaryotes and cyanobacteria.
• To explore the environmental conditions favoring microbial carbonate precipitation, particularly in Precambrian ecosystems.

Main Methods:

• Analysis of microbial roles in rock leaching and acid production (carbonic and organic acids).
• Examination of microbial precipitation of calcium carbonate under both aerobic and anaerobic conditions.
• Investigating the contribution of cyanobacterial communities and stromatolite formation in Precambrian environments.

Main Results:

• Organotrophic organisms initiate rock leaching, releasing CO2 and forming carbonic acid.
• Anaerobic microorganisms produce organic acids, with sulfate reducers and methanogens precipitating calcium carbonate.
• Cyanobacteria, particularly in benthic communities at ecotones, were precursors to stromatolite formation, a major Precambrian structure.

Conclusions:

• Microbial communities are fundamental to maintaining Earth's neutral conditions via the calcium cycle.
• Prokaryotic activity, from rock leaching to carbonate precipitation, underpins the geochemical calcium cycle.
• Specific microbial ecotones, involving cyanobacteria, were critical for early carbonate deposition and the formation of stromatolites.