I'm curious about that, too. I'm guessing that the original dates were based on dating of a few (too few) samples of younger intrusions or younger material that was later incorporated into the sediments.
Added by edit:
I will also add that I am getting the impression is that the initial dates were confirmed by the presence of relatively advanced metazoans. In fact, confirmed older dates will have some exciting implications about the evolutionary history of metazoan life.
This is on my list of things to investigate further. Exciting stuff!
Edited by Chiroptera, : No reason given.
Speaking personally, I find few things more awesome than contemplating this vast and majestic process of evolution, the ebb and flow of successive biotas through geological time. Creationists and others who cannot for ideological or religious reasons accept the fact of evolution miss out a great deal, and are left with a claustrophobic little universe in which nothing happens and nothing changes.
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M. Alan Kazlev
™ Version 4.2
