Now an abandoned gold mine in South Dakota is allowing the deepest look yet into this secret world of buried biodiversity. In new research published in the journal Environmental Microbiology, a genetic analysis of the mine’s microbes from as deep as 1.5 kilometers beneath the surface reveals a schism in survival strategies. Some microbes have big, bulky genomes that prep them to digest any nutrient that might come their way. Others are so genetically streamlined that they can’t even make some of life’s fundamental building blocks and instead rely on scavenging them or living symbiotically with other species.