Our 4.54 Billion year-old planet should remain habitable for the next 1.75 billion years, unless the humans or our next generations deteriorate our planet with a nuclear holocaust, runaway greenhouse emissions, or some other ecological disaster.

There is always a chance or possibility of encounter with a huge and wandering asteroid or a meteor, but as far as the sun's output and expansion are concerned the humans are left with plenty of time on Earth.

If the humans spare the earth and stop pumping extra CO2 into the atmosphere, the earth seems to be habitable for around 6.29 billion more years.

Andrew Rushby of the University of East Anglia and the lead author of a paper (PDF) published in the journal Astrobiology entitled "Habitable Zone Lifetimes of Exoplanets around Main Sequence Stars".

Rushby also tries to explain in his blog post that the true motivation and purpose of his paper was to explore methodologies for determining the habitability of exoplanets that share earthlike characteristics. Also, it was to make a definitive statement about our check-out time from our comfortable digs on Hotel Earth.

Rushby's paper takes into account a broad range of exoplanetary variables and concludes that a number of candidates may have habitable lifetimes that far exceed that of the Earth.