Microorganisms have shaped Earth's biological and ecological landscape since the emergence of the first living cells. This review explores microbial evolution through major origin-of-life theories, including the Last Universal Common Ancestor (LUCA), the primordial soup hypothesis, and the hydrothermal vent theory. It highlights the diverse mechanisms of microbial communication—such as quorum sensing and interspecies electron transfer—and their roles in symbiosis, immunity, and ecosystem regulation. Key microbiome-mediated pathways, including the gut-brain, gut-skin, and soil-gut axes, are examined in the context of human health. The review also addresses the consequences of reduced microbial exposure due to modern lifestyles and urbanization. Applications in agriculture, medicine, and astrobiology are discussed, including microbial fuel cells, bio-mining, and planetary protection strategies. By synthesizing ancient origins with futuristic innovations, this review underscores the crucial role of microbes in shaping both Earth's biosphere and humanity's future in space.
Keywords: Microbes, Hygiene hypothesis, LUCA, Astrobiology, Microbial axis
