How does it determine the upper and lower boundaries of the biosphere?

The boundaries of the biosphere are determined, first of all, by the existence of living organisms. Scientists set the upper boundary of the biosphere at the level of the planet’s ozone layer (15-20 km), which traps UV rays. The lower boundary of the biosphere is at the level of 3-7.5 km deep into the lithosphere. Although living organisms live much higher, scientists have determined the lower limit at the beginning of the process of decomposition of proteins.In the aquatic envelope, the biosphere boundary runs along the ocean floor at a level of 11 km.