4 ms·

What does half life of 500,000 years mean? Does that mean any given gene will, on average, split every 500,000 years? Or become unusable in 500,000 years? 65 m

What does half life of 500,000 years mean? Does that mean any given gene will, on average, split every 500,000 years? Or become unusable in 500,000 years? 65 million years would mean 130 halvings. Basically nothing left, then. ...but this may depend on environmental conditions. this must depend on average environmental temperature, right? Might dinosaur specimens in Antarctic or Arctic regions have experienced significantly lower average environmental temperatures? That could increase the half life significantly. Maybe we'll find Cryolophosaurus DNA some day... EDIT: the DNA degradation study specimen was in the south island of New Zealand, which had an average burial temperature of 13C. Antarctica along the coast has an average annual temperature of about -10C. Further inland and at higher elevation, it's much colder and dryer. Both those increase DNA stability. It's not crazy to me that you might have a factor of 100x greater stability for specimens found where the average temperature over the last 65 million years was 20-40 degrees colder and also dryer. EDIT AGAIN: Just to support what I said, it seems like a difference of average burial temperature of just 2.5 degrees C doubles the half-life of DNA (and this is multiplicative), so with a 20 degree difference in average burial temperature, that would be 8 doublings of half-life length (factor of 256), so instead of 500,000 years until the DNA was all broken up, you could have 128 million years. https://figshare.com/articles/_Predicted_DNA_half_life_for_varying_average_soil_temperature_for_each_fragment_type_/1420162 https://figshare.com/articles/_Predicted_DNA_half_life_for_v...

gnramires 7y ago
Not sure where his 500k years figure comes from. A cursory search gives 521 years: https://www.nature.com/news/dna-has-a-521-year-half-life-1.11555 https://www.nature.com/news/dna-has-a-521-year-half-life-1.1... Chemical decay tends to follow Arrhenius equation: https://en.wikipedia.org/wiki/Arrhenius_equation#Equation https://en.wikipedia.org/wiki/Arrhenius_equation#Equation so indeed a difference of maybe 40C should lead to a difference in half life of about 20-30%. I think about 30 half lives (~10^-9 degradation factor) should be the limit of recoverability, so perhaps 521x30 = 15k years in normal conditions up to 521x30x1.25 = 20k years in low temperature. Of course, other factors such as humidity could contribute as well to the half-life, and reactivity is a lot more complicated than the Arrhenius model in reality. But even then I would be surprised such a vast difference in reactivity outside of true cryogenic conditions (maybe even shielding from radiation?). edit: your second edit is interesting :) is that curve polynomial or exponential?
- Robotbeat 7y ago
  Looks exponential to me. After all, the Arrhenius equation (whose constants seem different here than your earlier assumptions) is exponential.
  - gnramires 7y ago
    Oh yes, I definitely messed up my calculations. Half life is (inversely) proportional to the reaction rate itself I guess (I were associating it with the exponent, because half life is usually in the exponent), so the half life itself would be proportional to exponential reciprocal of temperature (e^(a/T)). This means significant differences in HL for minor temperature variations under e.g. Arrhenius model (consistent with your graph I think). To extrapolate it some parameters need to be estimated though, which sounds interesting, I'll get around to that later...
jerzyt 7y ago
You raise a very good question. Unlike C14 dating, where the halflife is independent of environmental conditions, DNA is a chemical molecule, whose decomposition is a chemical reaction, dependent on exposure to time, temperature, pressure, light, and chemistry of the environment. I was hoping the article would explain why the conditions would be so favorable to make it possible.
- Robotbeat 7y ago
  Right. There must have been trillions of dinosaurs over the eons. Perhaps some individuals were buried in areas with colder conditions and chemical preserving agents. It may take a long time for us to find out.
EmilioMartinez 7y ago
>65 million years would mean 130 halvings. Basically nothing left, then Nah, we just need to find roughly 2^130 dinosaur cells, and the rest is statistics...

gnramires 7y ago

Not sure where his 500k years figure comes from. A cursory search gives 521 years: https://www.nature.com/news/dna-has-a-521-year-half-life-1.11555 https://www.nature.com/news/dna-has-a-521-year-half-life-1.1... Chemical decay tends to follow Arrhenius equation: https://en.wikipedia.org/wiki/Arrhenius_equation#Equation https://en.wikipedia.org/wiki/Arrhenius_equation#Equation so indeed a difference of maybe 40C should lead to a difference in half life of about 20-30%. I think about 30 half lives (~10^-9 degradation factor) should be the limit of recoverability, so perhaps 521x30 = 15k years in normal conditions up to 521x30x1.25 = 20k years in low temperature. Of course, other factors such as humidity could contribute as well to the half-life, and reactivity is a lot more complicated than the Arrhenius model in reality. But even then I would be surprised such a vast difference in reactivity outside of true cryogenic conditions (maybe even shielding from radiation?). edit: your second edit is interesting :) is that curve polynomial or exponential?

Robotbeat 7y ago
Looks exponential to me. After all, the Arrhenius equation (whose constants seem different here than your earlier assumptions) is exponential.
- gnramires 7y ago
  Oh yes, I definitely messed up my calculations. Half life is (inversely) proportional to the reaction rate itself I guess (I were associating it with the exponent, because half life is usually in the exponent), so the half life itself would be proportional to exponential reciprocal of temperature (e^(a/T)). This means significant differences in HL for minor temperature variations under e.g. Arrhenius model (consistent with your graph I think). To extrapolate it some parameters need to be estimated though, which sounds interesting, I'll get around to that later...

jerzyt 7y ago

You raise a very good question. Unlike C14 dating, where the halflife is independent of environmental conditions, DNA is a chemical molecule, whose decomposition is a chemical reaction, dependent on exposure to time, temperature, pressure, light, and chemistry of the environment. I was hoping the article would explain why the conditions would be so favorable to make it possible.

Robotbeat 7y ago
Right. There must have been trillions of dinosaurs over the eons. Perhaps some individuals were buried in areas with colder conditions and chemical preserving agents. It may take a long time for us to find out.

EmilioMartinez 7y ago

>65 million years would mean 130 halvings. Basically nothing left, then Nah, we just need to find roughly 2^130 dinosaur cells, and the rest is statistics...