"How did they know what the centre of the world is - I mean going round - how did they know it was Greenwich ?"
A longish discussion/lecture followed, taking in how to reckon noon time (when the shadows are shortest), why there are sixty minutes in an hour and sixty seconds in a minute, the formation of the Royal Society and the Greenwich Observatory ...
"Where did language come from ? How is it we say 'wood' for wood ?"
"Who invented numbers ?"
"How was electricity discovered ? Who thought of it ?"
My middle son used to throw this kind of stuff at me when it was bedtime and he didn't want to go up - he knew that I could never resist an answer (and he's doing maths and science A-levels after his GCSEs) - and I can't. I'm delighted when they ask questions - especially largeish ones.
I try in answering to emphasise that there are very few giant leaps (the mp3 player did not appear out of nowhere), that each new step is usually based on what went before, that simple things which make other things possible - the wire, the screw - could only be invented given the work of predecessors. You can't invent wire before you've got metal.
It's asking questions and trying new things that's taken us this far. In the days when we were bashing animals (and each other) on the head with flint axes, who had the idea of crushing two types of rock together, mixing with sand, heating the lot then blowing air through the hot rocks ? Yet it's a good job someone did.
I keep six honest serving-men
(They taught me all I knew);
Their names are What and Why and When
And How and Where and Who.