Where does this image come from? It opens more questions to me than it answers. For one, why is there a decrease in what appears to be the mid 80's? Second, the natural sources appear much less than 50% of total so that seems to contradict the text of the articles where it is used.
And finally, who added the notations -- are they accepted as accurate or guesses? 69.125.146.118 (talk) 12:02, 13 May 2008 (UTC)
