"Earth's lifespan" is slightly misleading if we're talking about inevitable future catastrophes of physics. What's more important is the lifespan of earth as a

"Earth's lifespan" is slightly misleading if we're talking about inevitable future catastrophes of physics. What's more important is the lifespan of earth as a hospitable planet and that's significantly less time (since the sun is heating up). From http://en.wikipedia.org/wiki/Sun#Life_cycle http://en.wikipedia.org/wiki/Sun#Life_cycle "...the Sun is gradually becoming more luminous (about 10% every 1 billion years), and its surface temperature is slowly rising. ... The increase in solar temperatures is such that already in about a billion years, the surface of the Earth will become too hot for liquid water to exist, ending all terrestrial life". So (using the numbers from this article) we have about 1 billion years to get off this rock, leaving another 2.7 billion on other planets before time ends. Not a bad run if we can make it. :)