 The combined domains of archaea and bacteria make up the most diverse and abundant group of organisms on Earth and inhabit practically all environments where the temperature is below +140 °C.They are found in water, soil, air, as the microbiome of an organism, hot springs and even deep beneath the Earth's crust in rocks.The number of prokaryotes is estimated to be around five nonillion, or 5 × 1030, accounting for at least half the biomass on Earth.