Odds of finding superbug in soil?
What is the deepest place in the crust that has been found to harbor life?


The deepest living animal:


That award goes to the "Devil Worm" (Halicephalobus mephisto), a nematode that has been found living at 3.6 km below the surface!! 


Halicephalobus mephisto is tiny (only 0.5mm long), and represents the deepest multicellular organism ever found. 


The original paper can be found here: Borgonie et al. (2011)


I should note, that the paper found definitive Halicephalobus mephisto at 1.3km depth, but found rRNA gene sequence belonging to a specimen of Monhysteridae at the deep 3.6km depth.



Do these microbe abundances and diversity change with depth?

According to  Inagaki et al (2015), microbe density is very low at low depths:


  By counting the cells of these microbes, they also conclude that it is a small community, with just one cell in a cubic centimetre of sediment in some sections of the sediment