Someday the Sun will burn out, and the solar system as we know it will be gone. Perhaps humans of the future will survive for a few more million years by moving to another star where they will find another planet. But someday even that will be gone. The whole universe will degenerate into a thermodynamic blandness that will make all intelligent life impossible. All that we built here on earth will be seen no more. None of our descendents will be around. Civilization will perish. Some people would say that life therefore has no meaning, but I disagree.
See The Meaning of Life for more.