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What is the oldest sample of genetic material (presumably DNA) identified? What are the prospects of pushing back much further into the geologic record?

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419 million year old DNA from halophilic bacteria.

http://news.discovery.com/earth/oldest-dna-bacteria-discovered.html

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My understanding was that DNA in non-living matter had lifetimes of thousands of years, not millions. How did such ancient DNA manage to be preserved? Does this result hold up? –  Poshpaws Oct 10 '12 at 14:52
    
Before DNA there was RNA. But ever heard of the polymerase chain reaction? See DNA and RNA don't actually need enzymes to replicate or a live cell. If you heat up and cool down DNA or RNA at certain temperatures and add in bases/nucleotides it will go ahead and do it by itself to make more DNA or RNA. Evolutionarily it's likely RNA came first, whilst the molecule itself was preserved (because it could self replicate) it wasn't conserved (the order of bases didn't matter so they swapped a lot). DNA is more stable, put RNA on a bench and it quickly degrades, so that's why DNA was required. –  AndroidPenguin May 4 '13 at 8:56
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I rather think that if the proper chemical conditions can preserve the molecules within tissue, you can find very old DNA. In this case the bacteria were preserved in crystalized salt and this seems to have kept the DNA intact. Other examples are from insects preserved in amber and tissues from animals who were buried in permafrost. –  shigeta May 4 '13 at 21:31
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