Some time in the next 1.5 billionâ `` 4.5 billion years , the axis 's tilt may begin to change into bad versions , with changes in the axis 's tilt of up to 90 Â . Some time in the next 1.5 billionâ `` 4.5 billion years , the axial tilt of the Earth may begin to undergo chaotic variations , with changes in the axial tilt of up to 90 Â .