For 3.8 billion years, microbial processes etched their indelible mark upon the geochemistry of Planet Earth, giving rise to extreme transformations - from the formation of granite during the early Archaean to the rise in atmospheric oxygen with oxygenic photosynthesis. Even now, atmospheric/climactic homeostasis and the non-equilibrium chemical speciation of most of the elements in the planet's crust & oceans are due, almost exclusively, to microbial metabolism. In addition to being the architects of the physiochemical world, prokaryotes have a 2 billion-year evolutionary head start on higher organisms, exhibiting an incredible diversity of physiologies, with population sizes and generation times that are more amenable to experimentation than macro-organisms. Thanks to emerging technologies (next-generation sequencing and high-resolution mass-spectrometry), scientists are beginning to appreciate the overwhelming complexity of microbial regulatory processes, behaviors, and interactions in the environment. A more thorough understanding of the ecology, evolution, and biochemistry of these prolific nano-machines can help us tackle some of the biggest questions in biology and Earth science. The Earth Microbiome Project (EMP) is a systematic attempt to characterize patterns of global microbial taxonomic and functional diversity, with the aim of processing over 200,000 samples from around the planet. In its first two years, the EMP has sequenced over 10,000 samples (almost 1 billion sequences, representing ~280,000 OTUs), which have been uploaded to a publicly available database (www.microbio.me & github), with another ~50,000 samples in the processing queue. This work will enhance our capacity to model global biotic and abiotic dynamics, and expand the theoretical framework underlying ecology and evolution.