I am always amazed how thin the biosphere is - 3km down in the water , 3 up in the air - so roughly 1/1000 of the radius of the earth. And the vast majority of the biomass could probably be found in couple of hundred meters close to water level.
There is stuff living in rocks down to about 4km depth (the limiting factor is heat), including far below the seafloor. It's still an open question whether this biomass, some of which has been out of contact with the surface for hundreds of millions of years, exceeds the biomass of surface on Earth, but it's at least in the same ballpark.
It's kind of ambiguous how "alive" that biomass is as compared to life on the surface. If a bacterium reproduces every 10,000 years, how "alive" is it?
