Assuming we keep our world clean, Earth will last for over 50 billion years. After that, life will be restricted to the north and south polls because of massive, natural global warming, a giant, old sun, and oxygen escaping out of the atmosphere. Also, the moon is slowly moving away from the Earth. This will throw the Earth off balance and mess up the magnetic polls, causing extreme heating and more oxygen escaping. Then Earth will become like Mars, a dry, desolate, life-less planet. Soon after that, the sun will burn out and implode (not in a super nova, as our sun would have to be about 3 times more massive than it is now to explode). The dead, dry Earth will spin out of the ex-sun's orbit and fall into Saturn, Jupitar, another star, or a black hole. Untill then, you won't have to worry. As we speak, scientists are tying to make artificial plants that pump out oxygen at an enormous rate and suck up CO2 and CO from our cars and power plants. Then we can keep our cars running for al long as we want!