Biosphere
The biosphere is the layer of Earth where life exists. The biosphere can be compared to the peel of an apple: very thin. the biosphere extends from the deepest root systems of trees, to dark ocean trenches, to high mountaintops. The biosphere has existed for about 3.5 billion years, with its earliest life form being prokaryotes. Prokaryotes developed the chemical process called photosynthesis which produced oxygen. Over a long period of time, a mix of oxygen and other gases developed that could sustain new forms of life. Now we have millions of different species of plants and animals today.
sources:http://www.biodiversidad.gob.mx/v_ingles/planet/whatis_bios.html
sources:http://www.biodiversidad.gob.mx/v_ingles/planet/whatis_bios.html