 Earth 's biosphere has significantly altered its atmosphere . Oxygenic photosynthesis evolved 2 @.@ 7 Gya , forming the primarily nitrogen – oxygen atmosphere of today . This change enabled the proliferation of aerobic organisms and , indirectly , the formation of the ozone layer due to the subsequent conversion of atmospheric O2 into O3 . The ozone layer blocks ultraviolet solar radiation , permitting life on land . Other atmospheric functions important to life include transporting water vapor , providing useful gases , causing small meteors to burn up before they strike the surface , and moderating temperature . This last phenomenon is known as the greenhouse effect : trace molecules within the atmosphere serve to capture thermal energy emitted from the ground , thereby raising the average temperature . Water vapor , carbon dioxide , methane and ozone are the primary greenhouse gases in the atmosphere . Without this heat @-@ retention effect , the average surface temperature would be − 18 ° C , in contrast to the current + 15 ° C , and life would likely not exist . 
