Microbial diversities are ubiquitous in nature and found in air, water, land, and even in extreme temperature and pressure conditions. Microorganisms play a very important role in the ecosystem, although many microbes have been attributed to cause illness and fatalities to cause disease to humans, animals, and plants. However, the good thing is that microorganisms give the planet many vital services and functions, such as the cycling of nutrients through biogeochemical cycles (Carbon, nitrogen, Sulphur, phosphorous), and nitrogen fixation helps to maintain the productivity of soil. Overall 50–80% of global oxygen is produced from the ocean and the majority of this production happens from microorganisms. Additionally, microorganisms are the source of CH4 and CO2 emissions into the atmosphere by decomposition or degradation process. In addition, they also sequester carbon from the atmosphere and ocean and transform it into organic matter. Microbial carbon sequestration could be useful for the mitigation of global warming and produce biofuels and materials. This chapter will cover the diversity of microorganisms, their various modes of energy, gas production, carbon sequestration, nutrient cycling, and their effects on ecosystems and microbial impact on biogeochemical cycles and soil health.