There are two scenarios which I find likely to happen in the future. Both of these - unlike solar flares, aseroids, etc. - might well kill Life as we know it. One is the repetition of the Snowball Earth scenario (check Wikipedia) that already happened twice in earth history (complete glaciation + temperatures around -50 C, anoxic oceans; then hothouse). The presumed cause is hyperactivity of phototrophes that deplete CO2 and unfortuitous landmass position. The current concentration of CO2 is the lowest and the current global temperature is the lowest since the emergence of animals. The concentration is already so low that glaciation cycles had began again, and these are speeding up. We are well on the way to the next such episode. Life pulled through the last two times, but the familiar green plants and animals will not make it through.

The second likely scenario is a dramatic despinning/drastic obliquity change of the Earth in 500-600 Myr, as the Moon migrates outwards. That will certainly happen, the question is only when (there are actually suggestions that the obliquity WAS twice lower in the pre-Cambrian). After the loss of the tidal stabilization by the Moon, all bets are off. You can read a few long-term scenarios for Earth-Moon system in Lissauer's review: http://www.boulder.swri.edu/~luke/Papers/lissauer-etal-rotation-review-2000.pdf

We (the terrestrials) have great future ahead of us.

Спасибо. Слегка удивился, услыхав о полном оледенении.... Потом вспомнил что-то по архею и понял, откуда ветер дует.

Да, хорошие сценарии.