Is There DNA in Dirt?
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Is There DNA in Dirt?

You probably think most of what we know about
ancient life comes from fossils. Y’know like, bones and stuff in the ground Well, it turns out that there are lots of
other clues about the history of living things that are just waiting to be dug up. It’s just that they’re a lot smaller than
even your tiniest fossils. Like, I-definitely-can’t-see-them small. I’m talking about ancient DNA. These little bits of really old DNA are in
soil — as well as other places like ice, and at the bottoms of lakes or oceans — and
together, they’re what scientists call sedimentary DNA. They’re leftovers of long-departed plants
and animals: sloughed-off flakes of skin and pieces of hair; dropped feathers and eggshells;
and fallen leaves. And because of advances in our ability to
purify, amplify, and analyze DNA, we can now use these remnants to re-create what Earth
looked like tens — even hundreds of thousands — of years ago, all without fossils like
bones or teeth. Someday, sedimentary DNA may even tell us
about life on worlds beyond our own. And it’s kind of amazing that scientists
can find this ancient genetic material at all. Because DNA isn’t exactly a robust molecule. Once it’s exposed to the elements outside
of cells, DNA breaks down easily, especially in hot temperatures. So it’s no surprise that some of the oldest
sedimentary DNA comes from samples taken from the coldest places on Earth, like glaciers
in Greenland or Siberian permafrost. But there are other ways DNA can stick around. DNA can bind to charged particles in the soil
— specifically in clay — which protect the molecules from getting chewed up by enzymes
that are released by microbes in the dirt. And sometimes those microbes can help save
the DNA, too. Instead of breaking it down, bacteria can
actually incorporate sequences of other organisms’ DNA into their own genomes for safekeeping. But to unlock the secrets that are kept in
sedimentary DNA, scientists have to find it, and amplify it. For this, paleobiologists use a technique
called polymerase chain reaction, or P-C-R. They extract the DNA from a sample of mud
or ice, or whatever they’re interested in, and then make lots of copies of certain stretches
of it, so they can get a closer look. To do this, they add a bunch of nucleotides
– compounds that are the basic building blocks of DNA — along with an enzyme called
DNA polymerase. The enzyme uses those blocks to replicate
the DNA, ultimately making millions of duplicates. Armed with those copies, scientists can then
sequence the DNA and find out what sorts of plants and animals once occupied that little
spot of mud or ice many years ago. Unfortunately, PCR isn’t perfect, and sometimes
DNA polymerase amplifies the wrong thing, like DNA from the researcher and not the soil
sample. With a small cough, a tiny droplet of saliva
can make it into the tube. And PCR is so good at what it does, that it
takes a miniscule amount of outside DNA to ruin everything. But if researchers can keep their samples
and workspaces impeccably clean and keep out unwanted DNA, they can find amazing things. A lot of these things have to do with what
really happened when, in Earth’s history. Because sedimentary DNA is really helpful
in giving us a sense of how old a certain bit of genetic material might be. It’s not perfect, but because scientists
generally know how old the layers are that they’re digging in, if they find DNA in it,
it’s a good guess that the genetic info is that old, too. So for example, in 2009, a team of researchers
drilled a sample of sediment from the Yukon Flats in central Alaska. And they found sedimentary DNA in that sample
that showed that woolly mammoths roamed mainland Alaska just 10,500 years ago — that means
the hairy pachyderms survived at least 2,600 years longer than we originally thought! Another study found that bacteria were evolving
ways to be resistant to antibiotics 30,000 years ago, well before we ever came with the
idea for modern drugs. And in 2015, researchers reported that they
had found sedimentary DNA evidence of 8,000-year-old wheat in the British Isles, suggesting people
were farming the land a full 2,000 years earlier than previously thought. But other scientists have since contested
these results, arguing that the samples were – you guessed it – contaminated. Because we are DNA-based, too, contamination
is a constant concern. But some researchers think that the growing
science of sedimentary DNA, may help us find signs of life on other worlds, like Mars. It’s super cold there, after all, so if
DNA is or ever was around, there’s a good chance it’s preserved somewhere. We just need to find it, and either then bring
it back, or analyze it there, without contaminating it with any of Earth’s very abundant genetic
material. You know, easy peasy. So many secrets, right under our feet! Thanks for watching this episode of SciShow! And thanks especially to our Patreon patrons
who make this whole channel possible. If you want to help us share science with
the world, you can go to And if you just want to keep getting smarter
with us, go to and subscribe.

100 thoughts on “Is There DNA in Dirt?

  1. TAQ polymerasur ….our human DNA Polymerase will degrade at the temp required for PCR. TAQ comes from yellowstone hot springs, kinda cool……

  2. I've heard there are lots of viruses in the oceans that are specific to extinct species. I don't suppose you could learn that much about a species by examining it's viruses.

  3. I wonder how mich DNA has already infected Mars from the Curiosity rover. There had to be a few skin cells on that thing when it landed. Some scientist will find that skin cell in 2215 and say "Have humans secrety been on Mars for over 200 years??"

  4. Scishow video suggest: lichtenberg figures. (Path of least resistance, lightning, rivers, fractals etc)

  5. This video should probably have a different title, at first i was like "of course there is DNA in dirt – there are soil microbes." But then I watched the video and realized it is about something more remarkable.

  6. Makes me wonder what DNA remnants might be found in the Dogger Banks. It would be cool to be able to learn more about life in Doggerland before it flooded about 8,000 years ago.

  7. Our growing ability to extract information about the prior state of the Earth despite the passage of time and the monumental changes which have taken place is why I support actively attempting to spread life to other bodies in our solar system. Load a rocket with tardigrades and extremophile bacteria. Fire it into Europa. Fire one into Io. Fire one at Mars. Fire them everywhere there is even a one-in-a-trillion chance that something might not die instantaneously. It is shortsighted and ignorant to take steps to attempt to preserve the 'purity' of other bodies by sterilizing our spacecraft and the like. We should be actively attempting to seed life of any form on these other bodies. Those who wish to study those bodies "as they were" will have no problem whatever in doing so despite the changes such actions could cause.

  8. 29 religious people watched this… they're now rolled up in a corner crying.

    Don't worry… god did it… was definitely the work of Thor.

  9. That (mole?) on Hank's neck… It really looks like a mark on my screen. I see it moving so i know it's not, but it's still infusing me with that sense of irritation.

  10. so how long till we make jerrasic park? and then how long till we make a mistake and end up with Trex, Raptors and Trex Raptor cross breeds roaming the earth and eating us

  11. We can find DNA in the soil but not the supposed 'pee' tape starring the Donald. Priorities people. jk

  12. Everyone assumes scientists use gloves/lab coats to protect themselves – in reality lots of times it's to protect their work.

  13. if you bring a ham sandwitch to the vacuum of space and leave it there, how long will it remain edible?

  14. Neat! Since it's mostly traces of dna though, could they ever find enough to discover an unknown plant or species?

  15. Genrally skepticismis a useful thing. However skeptics should not be sitting on the sidelines , they should be working to prove their skepticism valid.Conservatism based on c conjecture has has slowed progress of human kind in so many venues

  16. Why is there growing DNA around…

    … You know what will happen so I just won't tell it. Anyways I hate those why is there (random stuff) around my anus comments

  17. @1:38 — "Bacteria can incorporate sequences of other organism's dna into their own genomes"… Does he mean by horizontal gene transfer?… or is he saying that bacteria can pick up the DNA from the dirt & incorporate it? I'm betting he means HGT… in which case he should explain what it means to the presence of the sedimentary DNA.

  18. So I'm not joking when I piss in the woods….and tell my friends, "excuse me, I want to leave some of my dna for the future well being of the forest.

  19. Question : our biological system, here on Earth, is centered around DNA as we know it. ACGT. But accoding to Sciensium (you know, the third Veritasium^^), we recently manufactured other components to DNA, that differs from LUCA's. The question is, if we can make something out of the system to create life, how can we be sure that a LUCA from another planet hadn't a totally different structure that doesn't work like our DNA, but still did the same job in the past ? How can we be sure we don't accidentally discard actual "life" from other planets because we think "that weird structure in the sediments doesn't look like what our biological system can present" or something ?

  20. Isn't it kind of flawed to think extraterrestrial life would be DNA based? Life could be fundamentally different than what we know from earth, couldn't it?

  21. Contamination can be easily avoided by addition of specific primers that anneals only desired dna and polymerase only amplifies them…

  22. Instead of DNA, I would expect a completely different chemical to store genetic info on Mars, unless an chunk of Mars carrying life really did seed life on Earth.

  23. DNA on other worlds aye?
    Well to make PCR work, the DNA would need to EXACTLY the same as that of our tiny wet rock floating in space.
    Otherwise DNA polimerase wouldn't work right?

  24. A scientific question: What kind of primers would the scientists use to amplify the genes? they could use the TATA box as a primer but we could miss out a gross number of species that also function without them…😑

  25. Few times I've been around that track
    So it's not just gonna happen like that
    'Cause I ain't no hollaback girl
    I ain't no hollaback girl

  26. w8. If layers of earth keep getting built up, why doesn't the Earth expand? Erosion only effects the top layers, right?

  27. Microbiologist here, I do a ridiculous amount of PCR. Just want to clear up the dramatic air that this video puts around PCR. If you handle the tubes reasonably (basically, wear gloves and don't put your fingers on the inside surfaces of the tube) then it's really not hard to avoid amplifying your own DNA, unless you're working with a human DNA sample in the first place. But if you're working with bacteria like this video implies, then a false positive from your own DNA is usually not the go-to diagnostic–there's a million other things a false positive more likely to be.

  28. A Russian team discovered a seed cache of Silene stenophylla, a flowering plant native to Siberia, that had been buried by an Ice Age squirrel near the banks of the Kolyma River. Radiocarbon dating confirmed that the seeds were 32,000 years old.

  29. "Sedimentary DNA will tell us about life on worlds beyond our own." Isn't that presupposing that not only will alien life be carbon-based but DNA-based?

  30. Can you teach us about natral auburn hair? Ive tryed to reaserch it and keep getting the same results. It usally just gets catigorized as red but its not red. I have auburn hair and it may be a mutation but i would love to learn more about it.

  31. Why do Americans call soil dirt? I mean dirt is something you don't want to get in your clothes or in your house. Soil is something which we need to survive.

  32. Scriptwriters: Be careful of imprecise wording like "for safekeeping" – you wouldn't want to be ascribing intention to microorganisms!
    K thnx,
    ~ A scientist

  33. Sure Mars is extremely cold, but that's not enough to keep the DNA safe there, in the end Mars is being exposed to a lot of radiation thus it's hard for the DNA to survive.

  34. my wife works for the company that makes the best kits for extracting, isolating and sequencing dna and rna taken from just such difficult to test sources. Their company was recently acquired primarily for that tech. It's very cool stuff and extremely interesting science.

  35. SOME scientists say COME ON MAN give me % so I know more, not this crap. This is the type of half assed science why ignorant creationist assume they have a leg to stand on. Stop this week form of mocumentory please. Untill then no sub abig old 👎👎👎 as this would get an F in a 4th grade science class. THINK WITH YOUR EYES OPEN

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