Either

Why are the colours of Autumn leaves so moving and beautiful? Can you really explain why we have the four seasons we do in England?

(Bonus for parents? Why do Autumn songs get to us! For example:

https://www.youtube.com/watch?v=xXBNlApwh0c Eva Cassidy

https://www.bing.com/videos/search?q=sptember+song&adlt=strict%2cstrict%2cstrict%2cstrict&view=detail&mid=85745ED3637495FD829085745ED3637495FD8290&&FORM=VDRVRV

Nat King Cole

Or

If it turns out that we really are the only planet with conscious life on it, does that make the universe less or more extraordinary? Are we more or less significant?

Or

Does the ordinary (non-specialist/expert), in the 21C, really know and understand more than their counterpart in the Middle Ages or do they simply know how to repeat the equivalent sentences of experts from their era? Do I really understand Gravity, Radiation and Big Bang or do I just know how to nod in the right places and pretend?! Does my understanding of smelling, tasting, hurricanes or cyclones or lightening, the movement and colour of clouds really go beyond theirs?
Or

If you had to decide between destroying all History Books and all Novels, which would you choose? Why?

Or

Do fish have a sense of time? What about birds? Midges? Tortoises?