Just as the Earth wasn't always around, it isn't scheduled to stay around forever, either.
The sun, like other stars, has a finite life span. It will grow up to be a red giant and descend into old age as a white dwarf.
And when the Sun does balloon up and become a red giant, which experts say will likely happen in a few billion years, its super-sized mass will be bloated enough to vaporize our world.
There's a chance, however, that the changing mass of the sun will cause Earth to move into a more distant and pleasant orbit. One mathematical calculation shows it would be theoretically possible for humans — if any are around long enough — to engineer such a move before it's too late.