Conversation so far:
How is Thor Heyerdahl related to the expedition of Easter Island?
Thor Heyerdahl organized the Norwegian Archaeological Expedition to Easter Island.
Who went with Thor Heyerdahl to the expedition of Easter Island?
The expedition's scientific staff included Arne Skjølsvold, Carlyle Smith, Edwin Ferdon, Gonzalo Figueroa and William Mulloy.

Question: When did they go?
Self-contained rewrite: When did Thor Heyerdahl's expedition go to Easter Island?