Genetic diversity in microbial communities provides an ideal metric for assessing the effects of environmental perturbations and deciphering community assembly rules. However, the complexity of soil bacterial communities has thus far confounded effective measurement. We have developed improved analytical methods and show not only that bacterial diversity is measurable but also the abundance distribution can be deciphered. Reanalysis of published reassociation kinetics of bacterial community DNA from pristine and metal contaminated soils indicates 10,000,000 distinct genomes occurred in the pristine soil, exceeding previous estimates by 3 orders of magnitude. Exposure to low and high metal pollution reduced the diversity 99.9 and 99.99%, respectively. Comparison of different distributions, including predictions from Hubble's neutral theory, showed that a Zipf or Log LaPlace function best fit the abundance distribution of genetic diversity in the three soils. These results dramatically reshape current views of bacterial community diversity and provide the means to rigorously map bacterial diversity in nature.