 Earth 's increasing surface temperature will accelerate the inorganic CO2 cycle , reducing its concentration to levels lethally low for plants ( 10 ppm for C4 photosynthesis ) in approximately 500 – 900 Ma . The lack of vegetation will result in the loss of oxygen in the atmosphere , so animal life will become extinct within several million more years . After another billion years all surface water will have disappeared and the mean global temperature will reach 70 ° C ( 158 ° F ) . Earth is expected to be effectively habitable for about another 500 Ma from that point , although this may be extended up to 2 @.@ 3 Ga if the nitrogen is removed from the atmosphere . Even if the Sun were eternal and stable , 27 % of the water in the modern oceans will descend to the mantle in one billion years , due to reduced steam venting from mid @-@ ocean ridges . 
