They are two skeletons, a man and a woman, that were discovered as early as Season 1, apparently are approximately 50 years old. The issue about the skeletons (who they are) is probably going to be answered in Season 6 as TPTB have said numerous times. I think they could be Rose & Bernard, Jin & Sun or even Jack & Kate. Although the importance of the black and white stones is currently unknown.
(MY THOUGHT) If so called Adam and Eve were discovered in 2004 and said to be 40 to 50 years old, the only relevant date is 50 years because that would make it 1954 which we know was visited during the time flashes by Locke, Sawyer, Juliet and company.