From Envirowiki

the Biosphere is basically the part of the Earth that contains life. It includes soil down to bedrock, and sometimes below (caves etc,, the oceans, most land masses, and the lower 10 kilometers or so of the atmosphere.

[edit] carbon squestration

The biosphere performs the important task of regulating the atmosphere, and the carbon content thereof. plants soak up carbon, and use it to create the cells which make them grow^{[reference needed]}. plankton in the oceans are also a large carbon sink.

when vegetation dies, it usually rots and releases it's stored carbon into the atmosphere, sometimes at the higher greenhouse potential gas Methane. sometimes though, the vegetation will form peat, or be covered in soil and rocks, due to a landslide etc, in such a case, the carbon will be trapped under ground, and, given enough pressure will form coal.

plankton and sealife act in a similar way, but for petroleum oil