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Comment by Ovah | Hacker News Reader

And DNA appears to have a half-life of 521 years. 101 million years is 194 817 half-lifes. Assuming the research is sound I wonder how the bacteria get around that limit.

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No, DNA does not have a half-life of 521 years. To give the correct citation: ''' By analysing mitochondrial DNA (mtDNA) from 158 radiocarbon-dated bones of the extinct New Zealand moa, we confirm empirically a long-hypothesized exponential decay relationship. The average DNA half-life within this geographically constrained fossil assemblage was estimated to be 521 years for a 242 bp mtDNA sequence, corresponding to a per nucleotide fragmentation rate (k) of 5.50 × 10–6 per year. With an effective burial temperature of 13.1°C, the rate is almost 400 times slower than predicted from published kinetic data of in vitro DNA depurination at pH 5. ''' from https://royalsocietypublishing.org/doi/10.1098/rspb.2012.174...

Or in laymens words: the half-life of a DNA molecule per nucleotide depends on the environment and is in the order of magnitude around 1 million years. Else, we would not have any ancient genomes by now.

Thank you. Yeah you hit the nail on its head: it's the environmental conditions that matter. Still it's impressive that a single whole genome has remained largely intact for 100M years or else the cell would not be able to replicate. However for the sequencing of ancient genomes no single genome has to be intact as fragments of many cells can be computationally pieced together into a complete template genome.

I'd expect DNA's half life would depend on the environmental conditions. The conditions on the surface of the earth and at the bottom of the ocean are vastly different.

DNA stabilizing:

Much lower T (below 0C) Practically no radiation (an ocean above you blocking it all)

DNA de-stabilizing: Corrosive chemicals spewing from a nearby volcano (but only if one is near you!) Radiation from said volcano and rocks (but they'd have to be closer still, due to shielding from the water)

So unless the 500 year half life is the "self-damaging" rate, I'd expect DNA at the bottom to last much longer.

The stability of any complex organic molecule depends very strongly on the temperature, acidity, presence of other components etc. Without reference to the precise conditions the number is meaningless.

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