Actually it will be well before that the Earth is uninhabitable. The Sun is gradually releasing more energy as the core piles up more helium and the hydrogen burning zone expands. If I recall correctly a few billion years ago when life first started it was 30-40% less luminous. Within another billion or two it is expected to make it so hot that Earth's oceans boil away and the surface becomes too hot for any life as we know it (other than some bacteria I suppose).
Sorry, the former astronomy geek in me took over for a second there.