Bacteria are the most numerous organisms on Earth; billions of them may be found in a handful of soil. They are also found in nearly every habitat, from the sea floor to icebergs and hot sulfur springs. Their wide distribution reflects the variety of metabolic adaptations which enable various bacteria to live in environments of unusual chemical and thermal characteristics. The immense biological success of bacteria undoubtedly results from these metabolic capabilities, coupled with small size, rapid reproductive rate, and the ability to form resistant spores and so survive adverse conditions. These characteristics permit bacteria to live in many habitats that are here today and gone tomorrow. A drop of rain in the soil will evaporate in less than a day, but in that time, a bacterium may have divided several times and produced spores, which will lie dormant when the drop dries.