The chorus of Fat Old Sun sounds awfully similar to Earth. Same chord progression and similar melody.
Smile opened up for Floyd, so it's definitely possible that the melody stuck with Dave Gilmour.
Smile - link
Floyd - link
Thoughts ?!
I thought that also when I first heard Fat Old Sun. I couldn't place where I had heard it previously but then it hit me. It may have been one of those unconscious nicks...
The chord progression in question and melody intervals are common enough that they've probably been 'invented' a thousand times. Yes, it's possible that Dave was influenced by Tim, and it's just as possible that they were both influenced by someone or something else.
Roughly a year exist between Smile recording Earth and Floyd performing Fat Old Sun (that's performing, not recording) so I suppose it's possible. There's nothing to say that FOS didn't precede Earth as an idea, although there would be no reason for Staffell to have heard it before penning Earth, so the notion that Smile have, in some way, influenced Floyd is feasible. Seb beat me to the punch with the alternate theory :-)