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Comment by esquire_900 | Hacker News Reader

> we found that up to 99.1% of the microbes in sediment deposited 101.5 million years ago were still alive and were ready to eat

> But the real secret of their remarkable survival lies in their metabolic rate. It is just slow enough for them to survive for such long periods.

That would imply their metabolic rate to be practically zero, 101 million years is such a long time that even the tiniest amount of activity would result in a depletion of resources. Does that mean they die, only to come back to live at a better time?

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> were ready to eat

Am I the only one who pictured the lab workers munching on 100M year old microbe colonies?

And you just made me picture a store bought "ready-to-eat" meal as a terrifying and hungry creature waiting for me to wake it up.

Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn

At those timescales you'd think they would have ceased to exist due to atomic half-life or radiation or something.

Only if they were primarily made up of radioactive isotopes. Ask the carbon-12 in them should remain stable.

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.

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.

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.

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 wondered that too. "Die" implies not just metabolic rate going to zero, but also cells "disassembling" too ("decomposing" feels a bit large-scale in this context).

It did say that there were microscopic amounts of oxygen in the sediment. Presumably, that was enough to maintain a minimally-small MR.

As they were buried deeper and deeper in the sediment, presumably oxygen levels fell lower and lower.

That will have caused selective pressure to manage to survive with so few resources. Those that can't simply become energy for others who can.

There are cells that don't need oxygen to survive. The fact that there is no oxygen in the environment doesn't mean that certain forms of bacteria cannot survive.

> The presence of dissolved O2, nitrate (NO3−), phosphate (PO4−), and dissolved inorganic carbon (DIC) throughout the sedimentary sequence from the seafloor to the volcanic basement indicates that cell abundance and activity are not limited by availability of electron acceptors or dissolved major inorganic nutrients. From the Redfield stoichiometry of net dissolved O2 reduction to net nitrate production in the sediment, the microbial cells have been inferred to consume oxygen coupled to oxidation of marine organic matter at extremely slow rates.

-- D’Hondt, S. et al. Presence of oxygen and aerobic communities from sea floor to basement in deep-sea sediments. Nature Geosci. 8, 299–304 (2015).

I with my phone had that kind of low power mode - asleep for millions of years, yet ready to wake up when needed

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