The population of the globe will rise to 20 billion and there won't be enough space for everybody on the planet. Some people will live on other planets; they will live on the moon or Mars. On the moon and on Mars there will be fewer natural resources but more spaces. Will people choose to live on Earth or on a new planet? If they like adventure, they will choose to leave Earth but if they are bored with life on Earth, they may go and live on