NASA has opened the door to the next generation of space discovery by announcing great plans for a base for humans to live on the surface of the moon forever. The project to build a base on the moon will begin soon after 2020, with astronauts living there within four years. The project comes after several excellent scientists and environmentalists asked humans to look beyond Earth to ensure the survival of the species  . Eventually, the moon will be a base for humans to explore the solar system and one day land on Mars. NASA began planning for the first moon landing since 1972 when George Bush, the US president, announced his new plan for space exploration four years ago. NASA has already talked about the design of the Orion spacecraft that will replace the old space shuttle fleet in 2010. The plan for the moon base, however, is the first detailed explanation of how NASA intends to prepare for the first manned exploration of deep space and a possible Mars mission within 30 years. Scientists also believe that the south pole on the moon contain rich natural gases such as the rare helium-3 that could be used as fuel for the generation of nuclear power. Besides, teams of astronauts living there for six months at a time would mine for hydrogen and oxygen to make water and possibly rocket fuel. The passage mainly talks about   _  .
the USA's new plan for space exploration how to build a base on the moon why to ensure the survival of the species where to get new natural resources