6 ms·

The half-life of DNA is ~521 years at 13.1°C. This dino is more than 100 million years old. Scientists have been working very diligently to try to recover DNA

by nemo 6y ago

The half-life of DNA is ~521 years at 13.1°C. This dino is more than 100 million years old. Scientists have been working very diligently to try to recover DNA from millions of years ago, but the reality is any DNA found has a very good chance of being from bacteria & other organisms from the more recent past. Still there are (disputed) claims to have found DNA that's millions of years old: https://www.scientificamerican.com/article/possible-dinosaur-dna-has-been-found/ https://www.scientificamerican.com/article/possible-dinosaur...

credit_guy 6y ago
Not clear to me how this meme that the half-life of DNA of about 500 years appeared. There is no concept of half-life for chemicals, there's one only for radioisotopes. For this particular mummified dinosaur, if they found lots of somewhat preserved soft tissue, maybe hundreds of pounds, chances are that there could be trillions of DNA segments. Very likely no single gene will be unbroken, but with many fragments broken in different places the theoretical possibility to reconstitute the genetic code is there. You also don't start from zero knowledge. Humans and birds share about 65% of the genetic code [1], and dinosaurs are closer to birds than humans are. [1] https://education.seattlepi.com/animals-share-human-dna-sequences-6693.html https://education.seattlepi.com/animals-share-human-dna-sequ...
- rolph 6y ago
  >There is no concept of half-life for chemicals< https://www.sciencedirect.com/topics/medicine-and-dentistry/plasma-half-life https://www.sciencedirect.com/topics/medicine-and-dentistry/... https://en.wikipedia.org/wiki/Biological_half-life https://en.wikipedia.org/wiki/Biological_half-life half life is a general term that is frequently used in biochemistry, enzyme kinetics, chemistry and nuclear physics as a general term it is converse of doubling time and is simply a measure of stability or observed activity https://en.wikipedia.org/wiki/Half-life https://en.wikipedia.org/wiki/Half-life
  - credit_guy 6y ago
    Ok, there's a concept of biological half-life, including the famous 5 hours for caffeine. Living bodies are extraordinarily similar though, for example we all have about the same temperature of 36 deg Celsius. Chemicals out in the open, that's a completely different story. To be more specific: [1] is a published article in Current Biology where they state they were able to fully sequence the genome of two mammoths, one of which was 44.8k years old. That would be 86 half-lives according to the meme of 521y half-life for DNA. 2^(-86) is roughly 10^(-26). By the logic of DNA half-life, reconstituting a 44.8k y.o. mammoth genome would be beyond utterly ridiculous. Still, here we are. [1] https://www.cell.com/current-biology/fulltext/S0960-9822(15)00420-0 https://www.cell.com/current-biology/fulltext/S0960-9822(15)...
    - nemo 6y ago
      When I first said the half-life of DNA is ~521 years at 13.1°C I was careful to include that temperature which made it clear that the decay of any organic material over time has more variables than merely time. Here's the article where that number comes from. https://royalsocietypublishing.org/doi/full/10.1098/rspb.2012.1745 https://royalsocietypublishing.org/doi/full/10.1098/rspb.201... Mammoth DNA preserved in permafrost can last longer. Temperature is a variable. But dinosaurs lived in a very warm time, much warmer than the Ice Age the mammoths lived in so there's no possibility of nature somehow preserving Jurassic fossils in ice/permafrost.
    - perl4ever 6y ago
      Well, what half-life do you think that article implies? I took a shot at the calculation, and I got 1375 years.* That suggests to me that, yes, the popular figure may be off, but what difference does it make when you're talking about dinosaurs? I mean it seems like you are implicitly saying that it's a huge exaggeration to claim 120,000 half-lives since the dinosaurs went extinct whereas it might be as little as 47,000. I don't think you're wrong. But raising 2 to either power overflows my calculator, so I don't see how it matters. *my calculation is very imprecise and ignorant of biology, but I think orders of magnitude are good enough when talking about exponentials. - the sample was 180 mg - the number of cells in that size sample might be 8e10.[1] - they had 17x coverage - log2(17/8e10) is about -32 - 44,000 years / 32 = 1375 [1] I got a number for cells/kg by assuming a human weighs 180 lbs and has the number of cells mentioned in this reference: https://pubmed.ncbi.nlm.nih.gov/23829164/ https://pubmed.ncbi.nlm.nih.gov/23829164/
- nemo 6y ago
  When you're looking at things this old the reality is any DNA found has a very good chance of being from bacteria & other organisms/contamination from the more recent than 100 million years ago past. Even if you come up with a really clever tool to find ancient DNA you have no guarantees of finding dino DNA nor any way to filter out the DNA from all the organisms of the past, virtually all unsequenced, that could be contaminants.
- nemo 6y ago
  While this thing is being referred to as "mummified" the fossil itself is a result of gradual processes that replaced the original form of the corpse with minerals. It's not dried meat in there. The find was a few years ago, so much has been written on the topic, and you should read what the discussions of experts on the topic had to say. I'm not sure if you read this link before but I encourage you to - it includes a nice summary of the issues. https://www.scientificamerican.com/article/possible-dinosaur-dna-has-been-found/ https://www.scientificamerican.com/article/possible-dinosaur...

by nemo 6y ago

credit_guy 6y ago

Not clear to me how this meme that the half-life of DNA of about 500 years appeared. There is no concept of half-life for chemicals, there's one only for radioisotopes. For this particular mummified dinosaur, if they found lots of somewhat preserved soft tissue, maybe hundreds of pounds, chances are that there could be trillions of DNA segments. Very likely no single gene will be unbroken, but with many fragments broken in different places the theoretical possibility to reconstitute the genetic code is there. You also don't start from zero knowledge. Humans and birds share about 65% of the genetic code [1], and dinosaurs are closer to birds than humans are. [1] https://education.seattlepi.com/animals-share-human-dna-sequences-6693.html https://education.seattlepi.com/animals-share-human-dna-sequ...

rolph 6y ago
>There is no concept of half-life for chemicals< https://www.sciencedirect.com/topics/medicine-and-dentistry/plasma-half-life https://www.sciencedirect.com/topics/medicine-and-dentistry/... https://en.wikipedia.org/wiki/Biological_half-life https://en.wikipedia.org/wiki/Biological_half-life half life is a general term that is frequently used in biochemistry, enzyme kinetics, chemistry and nuclear physics as a general term it is converse of doubling time and is simply a measure of stability or observed activity https://en.wikipedia.org/wiki/Half-life https://en.wikipedia.org/wiki/Half-life
- credit_guy 6y ago
  Ok, there's a concept of biological half-life, including the famous 5 hours for caffeine. Living bodies are extraordinarily similar though, for example we all have about the same temperature of 36 deg Celsius. Chemicals out in the open, that's a completely different story. To be more specific: [1] is a published article in Current Biology where they state they were able to fully sequence the genome of two mammoths, one of which was 44.8k years old. That would be 86 half-lives according to the meme of 521y half-life for DNA. 2^(-86) is roughly 10^(-26). By the logic of DNA half-life, reconstituting a 44.8k y.o. mammoth genome would be beyond utterly ridiculous. Still, here we are. [1] https://www.cell.com/current-biology/fulltext/S0960-9822(15)00420-0 https://www.cell.com/current-biology/fulltext/S0960-9822(15)...
  - nemo 6y ago
    When I first said the half-life of DNA is ~521 years at 13.1°C I was careful to include that temperature which made it clear that the decay of any organic material over time has more variables than merely time. Here's the article where that number comes from. https://royalsocietypublishing.org/doi/full/10.1098/rspb.2012.1745 https://royalsocietypublishing.org/doi/full/10.1098/rspb.201... Mammoth DNA preserved in permafrost can last longer. Temperature is a variable. But dinosaurs lived in a very warm time, much warmer than the Ice Age the mammoths lived in so there's no possibility of nature somehow preserving Jurassic fossils in ice/permafrost.
  - perl4ever 6y ago
    Well, what half-life do you think that article implies? I took a shot at the calculation, and I got 1375 years.* That suggests to me that, yes, the popular figure may be off, but what difference does it make when you're talking about dinosaurs? I mean it seems like you are implicitly saying that it's a huge exaggeration to claim 120,000 half-lives since the dinosaurs went extinct whereas it might be as little as 47,000. I don't think you're wrong. But raising 2 to either power overflows my calculator, so I don't see how it matters. *my calculation is very imprecise and ignorant of biology, but I think orders of magnitude are good enough when talking about exponentials. - the sample was 180 mg - the number of cells in that size sample might be 8e10.[1] - they had 17x coverage - log2(17/8e10) is about -32 - 44,000 years / 32 = 1375 [1] I got a number for cells/kg by assuming a human weighs 180 lbs and has the number of cells mentioned in this reference: https://pubmed.ncbi.nlm.nih.gov/23829164/ https://pubmed.ncbi.nlm.nih.gov/23829164/
nemo 6y ago
When you're looking at things this old the reality is any DNA found has a very good chance of being from bacteria & other organisms/contamination from the more recent than 100 million years ago past. Even if you come up with a really clever tool to find ancient DNA you have no guarantees of finding dino DNA nor any way to filter out the DNA from all the organisms of the past, virtually all unsequenced, that could be contaminants.
nemo 6y ago
While this thing is being referred to as "mummified" the fossil itself is a result of gradual processes that replaced the original form of the corpse with minerals. It's not dried meat in there. The find was a few years ago, so much has been written on the topic, and you should read what the discussions of experts on the topic had to say. I'm not sure if you read this link before but I encourage you to - it includes a nice summary of the issues. https://www.scientificamerican.com/article/possible-dinosaur-dna-has-been-found/ https://www.scientificamerican.com/article/possible-dinosaur...