a. The over-consumption of all the resources on the planet; resulting in eventual starvation of everyone; or
b. The imbalance of weight on certain continents which will, in turn, stop the earth from rotating which will cause:
i. Gravity to stop working
ii. The atmosphere to disappate
iii. One side of the earth to be perpetually freezing and the other side to be perpetually hot
resulting in the death of all humans.