How does life change when you dig deeper?
Extremophile bacteria and archea are living very deep beyond our imaginations. This is what you need for general composition at different depths. And this and this is for the deepest living organism known ! Following is image from (Manson et al 2010) which shows at what depth you will get bacteria 



Even more deeper, Wold's single species ecosystem, Desulforudis audaxviator which can be found 3 km below sea level.