The correct order of key events regarding the exploration of space, beginning with the earliest, is:
first humans in space, first humans on the moon, first space shuttle flights
This reflects the chronological progression of human space exploration:
- First humans in space: Yuri Gagarin's flight in 1961.
- First humans on the moon: Apollo 11 mission in 1969.
- First space shuttle flights: Beginning with the launch of the Space Shuttle Columbia (STS-1) in 1981.