Lesson Learned

(Adapted from conversation around the campfire last night). As we're all staring into the fire, suddenly a part of the log flares up:

Me:   Did you see that?  Where does that energy come from?

Son:   Hydrogen?

Me:    You think there's hydrogen inside the log?

Son:    No

Me:    What's in the log that burns?

Son:    Wood

Me:     Where does the wood come from?

Son:    The tree makes it

Me:     Where does the tree get energy?

Daughter:  From the sun!

Me:     Yes!

Son:     But isn't the sun hydrogen?