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.**
Hereโs the breakdown:
1. **First humans in space** - This refers to Yuri Gagarin's flight on April 12, 1961.
2. **First humans on the moon** - This refers to the Apollo 11 mission, where Neil Armstrong and Buzz Aldrin landed on the moon on July 20, 1969.
3. **First space shuttle flights** - The first space shuttle, Columbia, was launched on April 12, 1981.
This sequence accurately reflects the chronological order of these significant milestones in space exploration.