Why should we continue with space exploration?

This planet is finite in living space, resources such as Iron, Aluminum, etc, and in a billion years, we won't be able to live here anymore no matter how well we take care of the environment. We may have to find a new home much sooner than that. If the need does arrive quickly, I prefer to already have some experience navigating and working in outer space. Also, if we manage to have self sustaining colonies on Mars, the Moon or a space station, it is good insurance to continue the human race in the event of a comet striking the earth, or some other global catastrophe.