Microbialites offer geological evidence of one of the planet’s first ecosystems, possibly preserving long-term interactions between coevolving life and its surroundings. They represent one of the most persistent ecosystems on Earth, while being the oldest witnesses of the combined evolution between biosphere, geosphere and atmosphere. Their extensive spatiotemporal distribution makes microbialites a valuable archive of the evolution of life on Earth while providing an ideal system in the quest for extraterrestrial life. However, the complex interaction loops between environmental and biological forces involved in their formation are still up for discussion, after more than a century of research. In this presentation, I will focus on the recent and fossil formation of microbial mats in two harsh habitats in Argentinean and Chilean Patagonia utilizing both experimental and field data. The combination of microbiological and mineralogical investigations is now providing a clearer picture of the mechanisms behind various biomineralization processes. By applying these results to other microbialites outcropping at different spatial and temporal scales, these microbial carbonates provide critical data to improve the reconstruction of the dominant environmental conditions on early Earth and perhaps in other planets.