According to the geological records, earth has been around for around 4.5 billion years, although it was mostly molten magma for about half a billion years... The sun is gradually getting hotter and bigger, and over time, even in the absence of global warming — the man-made stuff — the sun will expand and it will overheat the earth. My guess is probably... there is only several hundred million years left.... Basically, if it took an extra 10% longer for conscious life to evolve on earth, it wouldn't evolve at all, because it would have been incinerated by the sun. ... It appears that consciousness is a very rare and precious thing, and we should take whatever steps we can to preserve the light of consciousness, and the window has been open; only now after four and a half billion years is that window open, that's a long time to wait ... I'm pretty optimistic by nature, but there's some chance that window will not be open for long, I think we should become a multi-planet civilization while that window is open, and if we do the I think probable outcome for Earth is even better, because then you know Mars could help Earth one day.