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How does carbon dating work? · Daniel and Kelly’s Extraordinary Universe

• 0:08
  Speaker 1: Hey Daniel, it's been a long time. Did you have
• 0:11
  Speaker 1: a nice holiday with your family? We did, thank you
• 0:13
  Speaker 1: very much. We did some of our favorite holiday traditions. Oh,
• 0:17
  Speaker 1: like like you cooked specific meals that you only cook
• 0:20
  Speaker 1: once a year or something like that. Well, you know,
• 0:22
  Speaker 1: one of our favorite holiday traditions is a little bit unusual.
• 0:25
  Speaker 1: It's trash Day, like when you roll your bins to
• 0:28
  Speaker 1: the street because I call that Tuesday. Does that count
• 0:32
  Speaker 1: as a holiday? CD? No? No, No. Trash Day is
• 0:35
  Speaker 1: a much bigger deal. It's when you take all the
• 0:37
  Speaker 1: stuff out of your closets, decide what you actually need,
• 0:40
  Speaker 1: and donate or throw away the rest of it. Oh,
• 0:43
  Speaker 1: I bet you find some real treasures. You know, every
• 0:46
  Speaker 1: year we try to go one layer deeper into the
• 0:49
  Speaker 1: archaeology of our closets. Do you think you'll ever reach
• 0:53
  Speaker 1: the back. I'm not even convinced a back exists anymore.
• 0:57
  Speaker 1: It might just be like an infinite stack of useless junk. Well,
• 1:02
  Speaker 1: maybe you'll get lucky and it will have compressed for
• 1:05
  Speaker 1: long enough that it will become diamonds or something, or
• 1:08
  Speaker 1: be a black hole in there that'll just eat you.
• 1:11
  Speaker 1: That's not lucky, that's less lucky. That's still interesting. Hi.
• 1:30
  Speaker 1: I'm Daniel. I'm a professor at UC Irvine and a
• 1:34
  Speaker 1: particle physicist, and I love throwing stuff away. I'm Kelly
• 1:38
  Speaker 1: Wayder Smith. I'm a parasitologist with Rice University, and I
• 1:41
  Speaker 1: love throwing stuff away. But my family doesn't know. Do
• 1:45
  Speaker 1: you guys have arguments about how many nostalgic elements to keep? Yes,
• 1:50
  Speaker 1: that might be the thing we argue about the most often. Actually,
• 1:53
  Speaker 1: And are you ever right where they really need something?
• 1:56
  Speaker 1: And you're like, Hi, you shouldn't have thrown away that
• 1:58
  Speaker 1: melon baller. I knew we would come in Andy very rarely.
• 2:02
  Speaker 1: And also, you know, with things like Amazon, it could
• 2:04
  Speaker 1: show up at your house in less than a day.
• 2:06
  Speaker 1: So even if I'm wrong, you can just get a
• 2:08
  Speaker 1: new melon baller. That's true. Amazon has undermined your argument.
• 2:13
  Speaker 1: That's right, That's right. You can always just use the spoon.
• 2:15
  Speaker 1: Am I right? Well? I feel like you might appreciate
• 2:19
  Speaker 1: the melonballer, but you'll appreciate the lack of the melonballer
• 2:22
  Speaker 1: even more. You know, nothing is better than negative space.
• 2:26
  Speaker 1: If you've succeeded in like cleaning out a closet or
• 2:29
  Speaker 1: cleaning out some corner of your room, and then you
• 2:30
  Speaker 1: can just appreciate the emptiness. I agree, I like not
• 2:34
  Speaker 1: trimping over things in the middle of the night because
• 2:36
  Speaker 1: I get up a lot the middle of the night.
• 2:37
  Speaker 1: I value that well. Welcome to the podcast Daniel and
• 2:40
  Speaker 1: Jorge Explain the Universe, in which we explore the meaning
• 2:44
  Speaker 1: of nothingness and the very fabric of space itself. We
• 2:48
  Speaker 1: take the whole universe apart from the junk in your closets,
• 2:52
  Speaker 1: to the junk between your toes, to the junk that
• 2:54
  Speaker 1: fills the whole cosmos. We want to understand it. We
• 2:58
  Speaker 1: want to take it apart. We want to understand what
• 2:59
  Speaker 1: it means when it's there and it's not there, and
• 3:01
  Speaker 1: how it all got to be the way that it is.
• 3:04
  Speaker 1: So what are we working on today? Then? Today we
• 3:07
  Speaker 1: are thinking about the universe as a sort of mystery.
• 3:10
  Speaker 1: I like to think of physicists as like detectives trying
• 3:13
  Speaker 1: to crack the murder mystery of the universe, Like what
• 3:16
  Speaker 1: happened here? We are showing up at the scene and
• 3:19
  Speaker 1: wondering how did it all get to be the way
• 3:21
  Speaker 1: that it is? And today you get to be the
• 3:24
  Speaker 1: forensic scientist that dates the dead body. That's always a
• 3:27
  Speaker 1: good character. That's right, because when you show but the scene,
• 3:30
  Speaker 1: you want to understand what happened. You want to put
• 3:33
  Speaker 1: things in order. You want to say, what this happened,
• 3:35
  Speaker 1: then that happened, then the other happened, like the Solar
• 3:38
  Speaker 1: system formed and then the Earth cooled and then life
• 3:40
  Speaker 1: evolved on the planet, or the Big Bang happened, and
• 3:43
  Speaker 1: then helium formed, and then much much later stars happened.
• 3:46
  Speaker 1: The whole point of doing science is to put the
• 3:49
  Speaker 1: universe in some sort of order. That's what a story is.
• 3:52
  Speaker 1: And I'm a firm believer in the philosophy that human
• 3:55
  Speaker 1: thinking is mostly about storytelling. And so in order to
• 3:58
  Speaker 1: do that, you have to figure out why, how old
• 4:01
  Speaker 1: is stuff, what came before what other stuff? You need
• 4:04
  Speaker 1: to have dates and clocks and times if you're going
• 4:07
  Speaker 1: to unravel the murder mystery of the universe. And there's
• 4:10
  Speaker 1: a lot of different ways that we've done that throughout
• 4:12
  Speaker 1: the years, and some of them work better for particular
• 4:15
  Speaker 1: kinds of mysteries than others. So what sort of mysteries
• 4:18
  Speaker 1: are we solving today? Well, of course we are interested
• 4:20
  Speaker 1: in the mysteries of deep time. What happened in the
• 4:23
  Speaker 1: first few moments of the universe. How long has the
• 4:26
  Speaker 1: Earth been around? And what's been going on? How did
• 4:29
  Speaker 1: everything come together? One of my favorite things about dating
• 4:33
  Speaker 1: stuff is discovering those surprises, those realizations like wow, oh
• 4:38
  Speaker 1: my gosh, the Earth is so much older than anybody
• 4:41
  Speaker 1: ever imagined, or that the universe is shockingly old, or
• 4:45
  Speaker 1: you know, for some people the universe might be shockingly young.
• 4:48
  Speaker 1: Maybe some people bought the universe had been around forever
• 4:51
  Speaker 1: or trillions of years. So anytime you get one of
• 4:54
  Speaker 1: these dates, it's this glorious moment where you get to
• 4:56
  Speaker 1: like pin down the universe and say, ah, now I
• 5:00
  Speaker 1: know something about you, and that like eliminates a bunch
• 5:02
  Speaker 1: of possibilities. When you're a reader digesting a mystery novel,
• 5:06
  Speaker 1: you have like lots of different options in your head.
• 5:09
  Speaker 1: Maybe it was this person, maybe it was that person,
• 5:11
  Speaker 1: maybe it was this third person. And as you get clues,
• 5:13
  Speaker 1: you get to eliminate possibilities, which finally reveals to you
• 5:17
  Speaker 1: the truth, right, what actually happened in the universe. The
• 5:20
  Speaker 1: story is revealed by elimination, and so those clues are
• 5:23
  Speaker 1: absolutely essential. But you're right, Kelly, that there's lots of
• 5:25
  Speaker 1: different ways to date things in the universe, and today
• 5:28
  Speaker 1: we're gonna be focusing on something a little bit more recent,
• 5:31
  Speaker 1: how we can use physics to understand fairly recent history
• 5:35
  Speaker 1: here on Earth. Oh, that sounds a lot less disgusting
• 5:39
  Speaker 1: than using flymaggots. Fly maggots, what are you talking about?
• 5:44
  Speaker 1: That's for dating things like you know, dead bodies that
• 5:47
  Speaker 1: you find like what stage are the fly eggs that
• 5:49
  Speaker 1: have been laid on the body? So that's you know,
• 5:51
  Speaker 1: we're working with like days to weeks there. So are
• 5:53
  Speaker 1: we working on that skill or are we working like
• 5:56
  Speaker 1: past the writing DiPT in phase. Definitely past the rotting
• 6:00
  Speaker 1: corpse phase. But I think you put your finger on
• 6:03
  Speaker 1: a really interesting point, which is that there are all
• 6:05
  Speaker 1: these clocks build into nature, right like maggots take a
• 6:09
  Speaker 1: certain amount of time to digest a corpse, or rocks
• 6:12
  Speaker 1: take a certain amount of time to cool, and these
• 6:15
  Speaker 1: clocks are things we can take advantage of in order
• 6:18
  Speaker 1: to figure out how old things are, how long they've
• 6:21
  Speaker 1: been digesting, or how long they've been cooling, or how
• 6:23
  Speaker 1: long they've been radioactively decaying. We don't get to like
• 6:27
  Speaker 1: design these things go back in the past and like
• 6:29
  Speaker 1: leave clocks in place to tell us how long things took. Instead,
• 6:33
  Speaker 1: we have to just take advantage of the clocks that
• 6:35
  Speaker 1: we find. And some of these clocks, as you say,
• 6:38
  Speaker 1: are really short lived, like they tell us about things
• 6:40
  Speaker 1: that happened just for over weeks. Some of them can
• 6:42
  Speaker 1: tell us about things that happened for billions of years,
• 6:45
  Speaker 1: and other ones can tell us about things that happened
• 6:46
  Speaker 1: in the last ten fifty thousand years, which is a
• 6:49
  Speaker 1: super interesting time for the story of human civilization, how
• 6:53
  Speaker 1: we got to be who we are. And of course,
• 6:56
  Speaker 1: it turns out physics plays a big role. I love
• 6:59
  Speaker 1: learning about this topic because it's so exciting to me
• 7:01
  Speaker 1: how we figure out what tools are the best ones
• 7:03
  Speaker 1: to use to explore the past. And I specifically like
• 7:06
  Speaker 1: hearing about sort of physics and chemistry sorts of tools
• 7:09
  Speaker 1: because my sense is that they're a little bit less
• 7:12
  Speaker 1: susceptible to uncertainty. So, for example, you know, temperature can
• 7:15
  Speaker 1: impact how fast those flies are developing. But maybe today
• 7:20
  Speaker 1: you're going to explain to me that chemistry and physics
• 7:22
  Speaker 1: aren't that straightforward either. It turns out to be a
• 7:25
  Speaker 1: twisty and complicated topic. And of course sewage is involved. Yea,
• 7:33
  Speaker 1: my wife is very happy to hear about that. And
• 7:35
  Speaker 1: so today on the podcast, we'll be answering the question
• 7:43
  Speaker 1: how does radiocarbon dating work? Well, should we start by
• 7:47
  Speaker 1: seeing what the listeners think? Yes, absolutely, I was curious
• 7:51
  Speaker 1: to hear what people had to say about this. Radiocarbon
• 7:53
  Speaker 1: dating is something I think a lot of people have
• 7:55
  Speaker 1: heard about. It's on television all the time, and we
• 7:58
  Speaker 1: date this and we date that. But I was wondering
• 8:00
  Speaker 1: if people like really understood the mechanism of it, like
• 8:03
  Speaker 1: what the physics is of these clocks? Why is there
• 8:06
  Speaker 1: a clock? Why does it start when you die? And
• 8:08
  Speaker 1: how do we read it out? So thanks very much
• 8:10
  Speaker 1: to everyone who participates in this segment of the podcast,
• 8:13
  Speaker 1: sharing your thoughts without a chance to prepare. If you
• 8:16
  Speaker 1: would like to participate in the future, please don't be shy.
• 8:19
  Speaker 1: I'll be gentle. It's fun. Just write to me two
• 8:22
  Speaker 1: questions at Daniel Njorge dot com. So before you hear
• 8:25
  Speaker 1: these answers, think to yourself, do you know how radiocarbon
• 8:29
  Speaker 1: dating works? Here's what people had to say. If we
• 8:33
  Speaker 1: find some animal spoon, let's say some dinosaur spone, but
• 8:38
  Speaker 1: it inside the Earth, and then we calculate the amount
• 8:41
  Speaker 1: of carbon cfteen specifically present in it. Through those calculations,
• 8:45
  Speaker 1: we can easily calculate the age of that skeleton. I've
• 8:50
  Speaker 1: heard it get called carbon fourteen dating before, so that
• 8:54
  Speaker 1: makes me think that it has something to do with
• 8:56
  Speaker 1: the isotope and the decay of that carbon. Adam, you
• 9:01
  Speaker 1: can do tet the age of organic objects by looking
• 9:06
  Speaker 1: at the ratio of carbon isotopes. I feel like carbon
• 9:12
  Speaker 1: dating is when like two particles of carbon or like connected.
• 9:19
  Speaker 1: I don't know, I don't really know anything about that.
• 9:22
  Speaker 1: I felt like the answers to these fell into two camps.
• 9:24
  Speaker 1: People who sounded like they really knew what they were
• 9:26
  Speaker 1: talking about and people who had maybe not even heard
• 9:30
  Speaker 1: of carbon dating. And to me, that's it's sort of
• 9:33
  Speaker 1: interesting that it's like an either or scenario, like maybe
• 9:36
  Speaker 1: either you're into the kinds of TV shows that this
• 9:40
  Speaker 1: is shown in, or maybe you're not watching and cis
• 9:43
  Speaker 1: or what was that ship bones where the archaeologist was
• 9:46
  Speaker 1: doing carbon fourteen dating? Yeah, what do you think? I
• 9:49
  Speaker 1: was pretty tickled by the answer that suggested that, like
• 9:51
  Speaker 1: carbon fourteen atoms are like hooking up. You know, they're
• 9:54
  Speaker 1: like on Tinder, He's still finding each other and making magic.
• 9:58
  Speaker 1: It was a clever the cuff response there. Yeah, I
• 10:02
  Speaker 1: like our listeners are funny, funny people, absolutely, and I
• 10:06
  Speaker 1: had a lot of fun digging into the details of this.
• 10:09
  Speaker 1: This is not something I use in my research and
• 10:11
  Speaker 1: so not something i'd really ever wrapped my mind around.
• 10:14
  Speaker 1: And one of my favorite things about this podcast is
• 10:16
  Speaker 1: that I get an excuse to go off and learn
• 10:18
  Speaker 1: about something I always wanted to understand but never really
• 10:21
  Speaker 1: given myself the time to dig into. So thanks for
• 10:24
  Speaker 1: the listener who suggested this topic. How can listeners suggest
• 10:27
  Speaker 1: topics to you? Just shoot you an email. Absolutely, if
• 10:30
  Speaker 1: there's something you'd like to understand, please just write to
• 10:33
  Speaker 1: me to questions at Daniel and jorhe dot com. We
• 10:36
  Speaker 1: put it on our list and we get to every
• 10:38
  Speaker 1: single one eventually. And I'm with you. There are a
• 10:41
  Speaker 1: few things I enjoy more than an excuse to study
• 10:44
  Speaker 1: a topic that's interesting that isn't part of my research program.
• 10:47
  Speaker 1: I know, And it's weird that sometimes you feel like
• 10:49
  Speaker 1: you need an excuse, you know, you don't just like
• 10:51
  Speaker 1: get to slice off a few hours of your day
• 10:53
  Speaker 1: and go read about how something works. For some reason,
• 10:55
  Speaker 1: I feel like I have to give myself the opportunity
• 10:58
  Speaker 1: and having to do a podcast on it, explained of
• 11:00
  Speaker 1: the books is a good excuse to go and actually
• 11:03
  Speaker 1: learn how something works. That is one of the weird
• 11:05
  Speaker 1: things about academia. You don't feel like you have a
• 11:06
  Speaker 1: lot of time to just sit and think. But I too,
• 11:09
  Speaker 1: have created a bunch of tricks in my life, you know, like, oh,
• 11:11
  Speaker 1: I'm going to write a book about ten emerging technology,
• 11:13
  Speaker 1: so I have to read about all of them and
• 11:16
  Speaker 1: so yeah, but at least we have these tricks, all right.
• 11:19
  Speaker 1: So what is carbon fourteen? Right? So, radiocarbon dating or
• 11:22
  Speaker 1: carbon fourteen dating uses this weird form of carbon called
• 11:26
  Speaker 1: carbon fourteen. And when we say carbon fourteen, that number
• 11:30
  Speaker 1: fourteen tells us how many nucleons there are in the atom.
• 11:35
  Speaker 1: So remember that an atom has electrons around it, and
• 11:37
  Speaker 1: in the nucleus there are protons and neutrons. Now, usually
• 11:42
  Speaker 1: carbon has six protons and six neutrons, and so that's
• 11:46
  Speaker 1: carbon twelve. That's like the vanilla kind of carbon, the
• 11:50
  Speaker 1: kind that makes up most of you. And if it's
• 11:53
  Speaker 1: in carbon dioxide, and everywhere in the atmosphere. So that's
• 11:56
  Speaker 1: carbon twelve, which is stable. Carbon fourteen is a weird
• 12:00
  Speaker 1: version of carbon. It's still carbon, So there are six
• 12:03
  Speaker 1: protons inside, but there's two extra neutrons, so it's like
• 12:06
  Speaker 1: a heavier nucleus. So that's what carbon fourteen is. And
• 12:10
  Speaker 1: do those neutrons want to stay there or do they
• 12:13
  Speaker 1: want to escape? So you know, the stability of the
• 12:15
  Speaker 1: nucleus is a really interesting and complicated question. Some collections
• 12:19
  Speaker 1: of protons and neutrons are stable. You can build carbon
• 12:23
  Speaker 1: twelve and have it sit in space and come back
• 12:26
  Speaker 1: a billion years later and it'll still be carbon twelve.
• 12:29
  Speaker 1: Other constructions are not stable, Like you had two more
• 12:32
  Speaker 1: neutrons and all of a sudden you have carbon fourteen.
• 12:34
  Speaker 1: It's not stable. It will fall apart after a few
• 12:37
  Speaker 1: thousand years. And this all comes down to how those
• 12:40
  Speaker 1: protons and neutrons like to put themselves together inside the nucleus.
• 12:43
  Speaker 1: Remember that the nucleus is only protons and neutrons, and
• 12:46
  Speaker 1: the protons are positively charged. The neutrons are neutral, of course,
• 12:50
  Speaker 1: and so initially you might wonder, like, well, how does
• 12:52
  Speaker 1: the nucleus stay together anyway? It's all positive charges. Why
• 12:56
  Speaker 1: don't they just blow each other apart? And there is
• 12:58
  Speaker 1: that desire, right, They definitely are pushing against each other,
• 13:01
  Speaker 1: But on the other hand, they're held together by a
• 13:04
  Speaker 1: much stronger force. The strong nuclear force sticks the protons
• 13:07
  Speaker 1: and the neutrons all together. So it's a delicate balance
• 13:10
  Speaker 1: in some cases between the strong force sticking it together
• 13:13
  Speaker 1: and the electromagnetic force trying to push it apart. You
• 13:16
  Speaker 1: have one prototon and one neutron held together by the
• 13:19
  Speaker 1: strong nuclear force. That's stable. And then when you've got
• 13:22
  Speaker 1: extra neutrons floating around so that they don't pair evenly,
• 13:25
  Speaker 1: is that what makes it unstable? Yeah, that's right. You
• 13:27
  Speaker 1: can actually think about the construction of the nucleus in
• 13:30
  Speaker 1: a similar way to how we think about electron orbitals.
• 13:34
  Speaker 1: You remember learning in like high school chemistry. The electrons
• 13:37
  Speaker 1: aren't all just buzzing around the nucleus the same way.
• 13:40
  Speaker 1: It's like one in the lowest energy level and another
• 13:42
  Speaker 1: one in the next energy level. They sort of fill
• 13:44
  Speaker 1: up and they get to like more and more elaborate
• 13:46
  Speaker 1: orbitals as they get to higher and higher energy. Well,
• 13:49
  Speaker 1: the nucleus is constructed sort of in the same way.
• 13:52
  Speaker 1: The picture you often have of the nucleus is just
• 13:54
  Speaker 1: like a scoopful of protons and neutrons, But that's not
• 13:57
  Speaker 1: really very accurate. It's more like there are shells, you're
• 14:01
  Speaker 1: like an inner core or protons and neutrons have clicked together,
• 14:04
  Speaker 1: and then you can surround that with another layer of
• 14:06
  Speaker 1: like protons and neutrons, and the most stable atoms are
• 14:10
  Speaker 1: the ones where those layers are filled. You've like clicked
• 14:13
  Speaker 1: in all the protons and neutrons. It's sort of like
• 14:15
  Speaker 1: making a roman arch. When you have all the bricks together,
• 14:18
  Speaker 1: they click together to make a very stable structure. If
• 14:21
  Speaker 1: you're just missing one, then it can be very unstable.
• 14:24
  Speaker 1: So I didn't do great in high school chemistry? Is
• 14:29
  Speaker 1: the reason that that sounds new to me? Because we've
• 14:32
  Speaker 1: learned this in the twenty plus years since I've been
• 14:35
  Speaker 1: in high school? Or is that something we usually just
• 14:36
  Speaker 1: sort of, you know, skip over in high school, or
• 14:39
  Speaker 1: what's the story there? How long have we known that? Well?
• 14:41
  Speaker 1: I think we're gonna have to interview your high school
• 14:43
  Speaker 1: chemistry teacher to really find the answer to that. Let's
• 14:46
  Speaker 1: dig deep into your past. In fact, we have them
• 14:48
  Speaker 1: here on the podcast Surprise Surprise is Your Life, Kelly,
• 14:53
  Speaker 1: I don't think they like to be very much. Let's
• 14:54
  Speaker 1: move on. No, my high school chemistry teacher would not
• 14:58
  Speaker 1: be happy to hear from me either. I think it's
• 15:01
  Speaker 1: a combination of both things. We have understood what's going
• 15:04
  Speaker 1: on in the nucleus much much better in the last
• 15:07
  Speaker 1: few decades because we've been shooting stuff at it and
• 15:10
  Speaker 1: breaking it up and seeing what's inside of it, and
• 15:12
  Speaker 1: it's a hard project. We've also been building heavier and
• 15:15
  Speaker 1: heavier nuclei to understand, like what are the limits of stability?
• 15:18
  Speaker 1: How many protons and neutrons can you stick together and
• 15:21
  Speaker 1: have something which will stick around for billions of years.
• 15:24
  Speaker 1: We have a whole podcast episode about what are the
• 15:26
  Speaker 1: heaviest stable atoms And we think, for example, there might
• 15:29
  Speaker 1: be an island of stability where you get like hundreds
• 15:32
  Speaker 1: of protons and neutrons stuck together to make new super
• 15:35
  Speaker 1: heavy stable elements nobody's ever seen before. So it's a
• 15:38
  Speaker 1: complex field of study and it's probably not taught in
• 15:40
  Speaker 1: high school chemistry because it's evolving, and also because it's messy,
• 15:44
  Speaker 1: and I don't think that high school sophomores aren't necessarily
• 15:47
  Speaker 1: ready for it. I'm not sure that I was ready
• 15:49
  Speaker 1: for the electron stuff either, But all right, so these
• 15:52
  Speaker 1: things aren't stable, and every once in a while the
• 15:54
  Speaker 1: neutrons get picked out. How long are we talking before
• 15:58
  Speaker 1: the neutrons get picked doubt? Does it take like weeks? Years, millennia?
• 16:03
  Speaker 1: What are we looking at? So every atom is different. Uranium,
• 16:06
  Speaker 1: for example, has a half life which is like the
• 16:08
  Speaker 1: age of the Earth, but carbon fourteen only lasts about
• 16:12
  Speaker 1: fifty seven hundred years. Now, remember when we say that,
• 16:15
  Speaker 1: we don't mean that there's like a little clock inside
• 16:17
  Speaker 1: every carbon and when the time expires, it dies. What
• 16:20
  Speaker 1: we mean is that that's how long it takes, like
• 16:22
  Speaker 1: a population of carbon atoms for half of them to decay.
• 16:27
  Speaker 1: Each individual one might take longer or less time, because
• 16:31
  Speaker 1: fundamentally it's a quantum mechanical effect. There's a randomness to
• 16:35
  Speaker 1: win these things decay. So like five seven hundred years,
• 16:38
  Speaker 1: that's much longer than any of us live. And so
• 16:41
  Speaker 1: certainly there was no scientists who was sitting around, you know,
• 16:44
  Speaker 1: watching these things for five thousand, seven hundred years. How
• 16:46
  Speaker 1: do we figure something like that out? That's a great question,
• 16:49
  Speaker 1: And you know if it did take fifty seven hundred
• 16:51
  Speaker 1: years for every carbon atom to decay, then you couldn't
• 16:54
  Speaker 1: measure that half life without waiting for the first one
• 16:57
  Speaker 1: to decay, would literally take thousands of year years After
• 17:00
  Speaker 1: one thousand years or three thousand years, you would have
• 17:03
  Speaker 1: seen none decay, and you still wouldn't know is the
• 17:05
  Speaker 1: half life five thousand years or five billion years right?
• 17:09
  Speaker 1: And you wouldn't get ten year. You need a very
• 17:12
  Speaker 1: understanding department chare that's right. And so it's the statistical
• 17:16
  Speaker 1: nature of that, the randomness that really helps you because
• 17:19
  Speaker 1: even though the half life is five thousand, seven hundred years,
• 17:22
  Speaker 1: after one hundred years, there is a chance that a
• 17:25
  Speaker 1: few of them will have decayed. So all you need
• 17:27
  Speaker 1: is like a lot of carbon atoms, millions and billions
• 17:31
  Speaker 1: and zillions. Unfortunately, there are a lot of them around,
• 17:33
  Speaker 1: and you just watch for a few years or even
• 17:36
  Speaker 1: a few months, and a few of them will decay,
• 17:38
  Speaker 1: and from that you can extrapolate. Right as soon as
• 17:41
  Speaker 1: you start to see some of them decay, you know
• 17:43
  Speaker 1: how likely it is for any of them to decay,
• 17:46
  Speaker 1: and from that you can calculate how long it would
• 17:48
  Speaker 1: take for half of them to decay as a decay
• 17:51
  Speaker 1: is does it go from carbon fourteen the carbon thirteen,
• 17:53
  Speaker 1: the carbon twelves, or does it go right from fourteen
• 17:57
  Speaker 1: to twelve? Does it lose two neutrons all in one step?
• 18:00
  Speaker 1: So actually, carbon fourteen doesn't decay to carbon twelve. What
• 18:04
  Speaker 1: it does when it decays is that it goes to nitrogen.
• 18:07
  Speaker 1: Like normal nitrogen is nitrogen fourteen, but it has seven protons.
• 18:13
  Speaker 1: So you go from something which has eight neutrons and
• 18:16
  Speaker 1: six protons that's carbon fourteen, into something that has seven
• 18:20
  Speaker 1: neutrons and seven protons. So you take one of the
• 18:23
  Speaker 1: neutrons and you do a beta decay into a proton,
• 18:26
  Speaker 1: and now carbon fourteen has flipped into nitrogen fourteen. And
• 18:30
  Speaker 1: to me, this is really cool because this is the
• 18:32
  Speaker 1: quantum mechanics of it. Like carbon fourteen is not totally stable,
• 18:36
  Speaker 1: but it's also not totally unstable, like it will stick
• 18:38
  Speaker 1: around for a long long time. It's like a particle
• 18:41
  Speaker 1: trapped in a little potential well, and nitrogen fourteen is
• 18:45
  Speaker 1: other state it can flip into is also a little
• 18:48
  Speaker 1: potential well. And like classically, if you had a particle
• 18:52
  Speaker 1: trapped in a little well, it could never get out.
• 18:54
  Speaker 1: So what happens is that this atom switches from one
• 18:57
  Speaker 1: state to another state even though there's like a potential
• 19:00
  Speaker 1: barrier in between it. It does this by quantum tunneling.
• 19:04
  Speaker 1: It's like an electron stuck in one little hole that
• 19:07
  Speaker 1: ends up in another little hole, even though it doesn't
• 19:09
  Speaker 1: have the energy to go over the barrier. So carbon
• 19:12
  Speaker 1: fourteen turns into nitrogen fourteen through this random quantum mechanical
• 19:16
  Speaker 1: tunneling process that lets a switch from one state to
• 19:19
  Speaker 1: a lower energy state without having enough energy to actually
• 19:23
  Speaker 1: go over the barrier in between them. That's another thing
• 19:25
  Speaker 1: I'm amazed we ever managed to figure out. I know,
• 19:28
  Speaker 1: so like quantum mechanics is happening all over the place
• 19:31
  Speaker 1: in the atmosphere right in front of us. That's crazy.
• 19:35
  Speaker 1: So where do we get carbon fourteen in the first place? Yeah,
• 19:38
  Speaker 1: carbon fourteen only sticks around for a few thousand years.
• 19:40
  Speaker 1: So you might wonder, like the Earth is billions of
• 19:43
  Speaker 1: years old, why do we have a new carbon fourteen?
• 19:45
  Speaker 1: And the only reason we do is that we have
• 19:47
  Speaker 1: a source of it, right, this new carbon fourteen being
• 19:50
  Speaker 1: made all the time, and of course it comes from space.
• 19:55
  Speaker 1: The Earth is not just sitting out in empty space.
• 19:58
  Speaker 1: Space is very far from We're being inundated with high
• 20:02
  Speaker 1: energy particles all the time, from the Sun, from black
• 20:05
  Speaker 1: hole accretion disks, from other galaxies. All sorts of stuff
• 20:08
  Speaker 1: are smashing into the Earth all the time. And then
• 20:12
  Speaker 1: we call these things cosmic rays, and when they hit
• 20:14
  Speaker 1: the upper atmosphere, they cause all sorts of reactions. They
• 20:18
  Speaker 1: smash into stuff and they change it. What happens is
• 20:21
  Speaker 1: a cosmic ray will smash into like a proton that's
• 20:24
  Speaker 1: in nitrogen, which is seven P seven N, and convert
• 20:28
  Speaker 1: it into a neutron. So you have nitrogen fourteen smash
• 20:32
  Speaker 1: banging with a proton, and you end up with carbon
• 20:34
  Speaker 1: fourteen because one of those protons has gotten converted into
• 20:38
  Speaker 1: a neutron. WHOA Okay, And that's all happening in the
• 20:41
  Speaker 1: atmosphere and not happening much on Earth, Is that right?
• 20:44
  Speaker 1: That's right, It's happening mostly in the upper atmosphere. Cosmic
• 20:47
  Speaker 1: rays can't just fly through the atmosphere. They interact with particles.
• 20:50
  Speaker 1: It's sort of like running into a crowd, right, You're
• 20:52
  Speaker 1: going to bang into all the other particles. Because cosmic
• 20:55
  Speaker 1: rays they're just particles. They sound spooky and weird, but
• 20:57
  Speaker 1: they're just particles. So these things are created in the
• 21:00
  Speaker 1: atmosphere and then they sort of drift down to the
• 21:02
  Speaker 1: rest of the planet. Okay, all right, so now we
• 21:04
  Speaker 1: know how we get carbon fourteen, and we should take
• 21:07
  Speaker 1: a break and when we come back, we'll talk about
• 21:10
  Speaker 1: how it goes from the atmosphere to being incorporated into
• 21:13
  Speaker 1: living things. And we're back. Okay. So carbon fourteen, made
• 21:31
  Speaker 1: by cosmic rays in the atmosphere, falls down towards the
• 21:35
  Speaker 1: living stuff that lives below. And then what happens, Daniel,
• 21:39
  Speaker 1: So carbon fourteen interacts with oxygen in the atmosphere to
• 21:42
  Speaker 1: make carbon dioxide, and so now you have these special
• 21:45
  Speaker 1: molecules of carbon dioxide. Most of the carbon dioxide in
• 21:48
  Speaker 1: the atmosphere has carbon twelve in its normal stuff, but
• 21:52
  Speaker 1: about one in a trillion has a carbon fourteen atom,
• 21:56
  Speaker 1: So it's carbon fourteen plus two normal oxygens. And this
• 21:59
  Speaker 1: is just floating out there around in the atmosphere. And
• 22:02
  Speaker 1: so when plants, for example, do photosynthesis and they breathe
• 22:05
  Speaker 1: in carbon dioxide, most of the time they're breathing in
• 22:09
  Speaker 1: normal vanilla carbon dioxide, but sometimes one in a trillion
• 22:13
  Speaker 1: to get the extra spicy version of carbon dioxide that
• 22:16
  Speaker 1: has carbon fourteen in it, so they take it in
• 22:19
  Speaker 1: and then when you eat your impossible burger, which is
• 22:22
  Speaker 1: made out of plants, you're eating that carbon fourteen that
• 22:25
  Speaker 1: got incorporated into the plant. So do plants have more
• 22:28
  Speaker 1: carbon fourteen than animals because they're sucking so much of
• 22:33
  Speaker 1: it out of the atmosphere or is that not how
• 22:35
  Speaker 1: it works? Carbon fourteen definitely flows through the sort of biosphere,
• 22:39
  Speaker 1: and its richest at the source. Like if you go
• 22:41
  Speaker 1: into the upper atmosphere, that's the highest fraction of carbon fourteen.
• 22:45
  Speaker 1: As you get further and further away from the source,
• 22:47
  Speaker 1: you get less and less carbon fourteen because it starts
• 22:50
  Speaker 1: to decay. Now it decays a really, really slowly, So
• 22:53
  Speaker 1: like most plants and most animals on the surface have
• 22:56
  Speaker 1: about as much carbon fourteen in them as exist in
• 22:58
  Speaker 1: the upper atmosphere. Like the bottom of the ocean, the
• 23:01
  Speaker 1: deep ocean doesn't interact with the atmosphere as often, and
• 23:05
  Speaker 1: so the rate of carbon fourteen down there is much
• 23:08
  Speaker 1: less because it takes longer to get down there, and
• 23:10
  Speaker 1: by the time it does, some of it has decayed.
• 23:13
  Speaker 1: And so like deep ocean animals tend to have less
• 23:16
  Speaker 1: carbon fourteen than like birds that live in the high
• 23:19
  Speaker 1: atmosphere or you know, cows that live on the surface.
• 23:22
  Speaker 1: We can actually map the carbon fourteen fraction over the
• 23:25
  Speaker 1: biosphere and see how that flows. Okay, And so in general,
• 23:28
  Speaker 1: we're also not really interested in like you know, there
• 23:31
  Speaker 1: are one hundred units of carbon fourteen in a tree.
• 23:35
  Speaker 1: We're interested in the relative amounts of carbon twelve compared
• 23:40
  Speaker 1: to carbon fourteen. Is that right? So it's about relative
• 23:43
  Speaker 1: amounts as opposed to absolute quantities. Yeah, exactly. And this
• 23:46
  Speaker 1: is the really fascinating bit about carbon fourteen. Right. First
• 23:49
  Speaker 1: of all, it's a natural clock. It's this thing that
• 23:51
  Speaker 1: happens in the universe. You create carbon fourteen, you have
• 23:54
  Speaker 1: about fifty seven hundred years until it decays. The fascinating
• 23:58
  Speaker 1: thing about carbon fourteen is that we use it to
• 24:00
  Speaker 1: date when something dies, right, we can tell when something
• 24:04
  Speaker 1: has died. And when I first heard about this, I thought, what,
• 24:08
  Speaker 1: how does like the carbon know that you've died. Is
• 24:11
  Speaker 1: it like as soon as you die your carbon fourteen
• 24:13
  Speaker 1: atoms start ticking or something. I thought that was really weird,
• 24:16
  Speaker 1: because you know, life and death is this holistic property
• 24:19
  Speaker 1: of an object, and like the carbon fourteen doesn't care
• 24:21
  Speaker 1: if you're alive or dead. Right, So the reason that
• 24:24
  Speaker 1: carbon fourteen is sensitive to your moment of death is
• 24:27
  Speaker 1: because of what you stop doing when you die, which
• 24:29
  Speaker 1: is you stop breathing and you stop eating, so you
• 24:32
  Speaker 1: stop getting new carbon fourteen. So all the carbon fourteen
• 24:36
  Speaker 1: in your body is always decaying. Like that clock started
• 24:39
  Speaker 1: when the cosmic array hit in the upper atmosphere, and
• 24:41
  Speaker 1: maybe it took a few hundred years before you ate
• 24:43
  Speaker 1: that carbon fourteen, and so that clock has already started.
• 24:46
  Speaker 1: What doesn't happen anymore when you die is that you
• 24:49
  Speaker 1: don't get any fresh carbon fourteen, and so now the
• 24:51
  Speaker 1: carbon fourteen in your body is decaying and it's not
• 24:54
  Speaker 1: being replaced. So something that died a long time ago
• 24:57
  Speaker 1: will have almost no carbon fourteen in it. If you
• 25:00
  Speaker 1: died ten minutes ago, you still have a lot of
• 25:02
  Speaker 1: carbon fourteen in you. So it's not really like the
• 25:05
  Speaker 1: moment of death. It's more like the moment you stopped
• 25:07
  Speaker 1: participating in the biosphere, which I guess is really the
• 25:11
  Speaker 1: same thing. Do you like the microbes that break you
• 25:14
  Speaker 1: down put some more carbon fourteen in there to mess
• 25:17
  Speaker 1: the clock up a little. I guess it doesn't matter,
• 25:19
  Speaker 1: because if the half life is five thousand, seven hundred years,
• 25:22
  Speaker 1: we're talking about like a week or two of microbes
• 25:24
  Speaker 1: messing up the values. Yeah, good question. I guess it
• 25:27
  Speaker 1: depends a little bit if they're aerobic or an aerobic. Right,
• 25:30
  Speaker 1: are they consuming CO two? I'll have to ask a
• 25:32
  Speaker 1: microbiologist about that. Check in with my wife about it later.
• 25:35
  Speaker 1: I thank you, no one. Yeah, that's right, that's very convenient.
• 25:39
  Speaker 1: And so this has a really interesting history. It was
• 25:41
  Speaker 1: like in the forties that people figured out, oh maybe
• 25:44
  Speaker 1: this is possible. People were studying carbon fourteen just from
• 25:47
  Speaker 1: like a chemistry point of view, like what is this stuff?
• 25:50
  Speaker 1: How long does it last? And at the time, you know,
• 25:52
  Speaker 1: we didn't really understand the nucleus very well. People were
• 25:55
  Speaker 1: making estimates for how long it might last, and the
• 25:58
  Speaker 1: measurements they made were really surprised, and they discovered, oh,
• 26:00
  Speaker 1: my gosh, this stuff lasts a lot longer than we thought.
• 26:03
  Speaker 1: They expected to have a much shorter half life, like
• 26:06
  Speaker 1: tens or hundreds of years, so when they discovered that
• 26:09
  Speaker 1: it has a half life of almost six thousand years,
• 26:12
  Speaker 1: they were surprised. But it also opened up this really
• 26:16
  Speaker 1: cool possibility. Why were they surprised, Like, did we expect
• 26:20
  Speaker 1: that half lives would be like similar between objects on
• 26:24
  Speaker 1: the periodic table and they ended up not being similar. Yes,
• 26:28
  Speaker 1: there are reason they were surprised, or just sometimes sizes surprising.
• 26:31
  Speaker 1: They were surprised because we just didn't understand the nucleus
• 26:34
  Speaker 1: of the atom very well. I mean, this is the forties, right,
• 26:36
  Speaker 1: Quantum mechanics were very very new, and so all of
• 26:38
  Speaker 1: our calculations of how things work in the nucleus were
• 26:41
  Speaker 1: very very rough and a lot of handwaving. I mean
• 26:43
  Speaker 1: even today, it's not easy to do these calculations to say,
• 26:47
  Speaker 1: like what would be the mass of this particle or
• 26:49
  Speaker 1: how stable would that be. You know, we have theories
• 26:52
  Speaker 1: about whether the super heavy elements would be stable, but
• 26:55
  Speaker 1: we can't say these things for certain because we don't
• 26:57
  Speaker 1: know how to do a lot of these calculations. Because
• 27:00
  Speaker 1: the strong nuclear force is very complicated. It's very very strong,
• 27:03
  Speaker 1: which means the calculations are very very sensitive to getting
• 27:06
  Speaker 1: things wrong. It's a kind of calculation where if you
• 27:08
  Speaker 1: start to get things a little bit wrong, the wrongness
• 27:10
  Speaker 1: gets amplified by the strength of the force instead of
• 27:13
  Speaker 1: like a decaying away. Like with gravity, if you get
• 27:16
  Speaker 1: the location of an asteroid a little bit wrong, it's
• 27:18
  Speaker 1: not going to propagate to becoming really really wrong later
• 27:21
  Speaker 1: on because gravity is so weak, so you can make
• 27:23
  Speaker 1: approximations and mostly get the right answer at least for
• 27:26
  Speaker 1: the foreseeable future. With the strong force, as soon as
• 27:28
  Speaker 1: you get something a little bit wrong, everything goes totally wrong.
• 27:31
  Speaker 1: So the short version is that nuclear physics is hard. Well,
• 27:34
  Speaker 1: that's not surprising, and so maybe they shouldn't have been
• 27:37
  Speaker 1: surprised because nuclear physics is hard. Okay. So you had
• 27:41
  Speaker 1: mentioned at the top of the show that sewage was
• 27:43
  Speaker 1: gonna come into the story at some point, and so
• 27:45
  Speaker 1: I'm hoping that now that we're talking about, you know,
• 27:47
  Speaker 1: when we figure out the whole carbon fourteen thing, is
• 27:50
  Speaker 1: this when we get to talk about the sewage. This
• 27:52
  Speaker 1: is when we get to talk about the sewage. Absolutely yea.
• 27:55
  Speaker 1: So it was in mid nineteen forties and Willard Libby,
• 27:59
  Speaker 1: who was at Berkeley, learned about these results that carbon
• 28:02
  Speaker 1: fourteen was surprisingly long lasting, and he thought, hey, that
• 28:05
  Speaker 1: would be a really cool way to figure out how
• 28:07
  Speaker 1: long something has been dead. And so what he did
• 28:11
  Speaker 1: is he moved to a new job at the University
• 28:12
  Speaker 1: of Chicago and he proposed this idea. He said, oh,
• 28:15
  Speaker 1: maybe this will work. And the first thing they did
• 28:18
  Speaker 1: was to study methane from the Boston sewage system. Right,
• 28:22
  Speaker 1: So methane is a gas, right, that's produced when sewage
• 28:25
  Speaker 1: basically ferments. Right, my grooves are consuming your sewage. And
• 28:29
  Speaker 1: so they gathered this and they measured the carbon fourteen
• 28:31
  Speaker 1: fraction in methane basically from Boston's dark matter, and then
• 28:36
  Speaker 1: they compared that to how much carbon fourteen there was
• 28:40
  Speaker 1: in methane from fossil fuels, right, Like the methane that
• 28:43
  Speaker 1: maybe you burn in your house comes from plants that
• 28:45
  Speaker 1: died millions and millions and millions of years ago. And
• 28:49
  Speaker 1: what they found is no surprise to us now, is
• 28:51
  Speaker 1: that the methane from the Boston sewis system has a
• 28:53
  Speaker 1: lot of carbon fourteen and the methane from fossil fuels
• 28:56
  Speaker 1: has none. All Right, So that's beginning to tell us
• 28:59
  Speaker 1: the limits for how we can use carbon fourteen for dating.
• 29:02
  Speaker 1: But I'll know you said that Libby had moved to Chicago,
• 29:07
  Speaker 1: but he looked at the Boston sewage is there, just like,
• 29:10
  Speaker 1: is Boston sewage the best sewage? Why did you travel
• 29:12
  Speaker 1: all the way to Boston? Was the Chicago sewage wasn't
• 29:16
  Speaker 1: disgusting enough. I'm sure those people who live in Boston
• 29:20
  Speaker 1: are very proud of their sewage. I have a little
• 29:22
  Speaker 1: glimpse into this because of my wife's research. You know,
• 29:24
  Speaker 1: she studies the microbes and sewage, and it can be
• 29:27
  Speaker 1: surprisingly tricky to get access to it. So I suspect
• 29:30
  Speaker 1: it's just a question of like politics and access. Not
• 29:33
  Speaker 1: every waste management system is interested in having scientists like
• 29:36
  Speaker 1: dig around in their facility, while others are you free
• 29:40
  Speaker 1: to share the science gold that is flowing through their pipes?
• 29:47
  Speaker 1: Politics and sewage? Yeah, so I suspect they had a
• 29:49
  Speaker 1: good Boston connect, you know, for some real primo Boston
• 29:52
  Speaker 1: sewage got it okay. So so by the time you
• 29:56
  Speaker 1: ask petroleum, there's no carbon fourteen and you start losing
• 30:00
  Speaker 1: carbon fourteen when you die. So can you use this for?
• 30:04
  Speaker 1: Is this helpful for like certain kinds of fossils? What
• 30:06
  Speaker 1: kind of things that we use this for? So far,
• 30:08
  Speaker 1: you can use this for basically anything that's died in
• 30:11
  Speaker 1: the last maybe fifty thousand years, because those things were
• 30:15
  Speaker 1: accumulating carbon fourteen as they were alive and participating in
• 30:18
  Speaker 1: the biosphere, and as soon as they died, then they
• 30:21
  Speaker 1: stopped and the carbon fourteen started to decay away. Now,
• 30:25
  Speaker 1: things that are much much older than that, they just
• 30:27
  Speaker 1: have zero carbon fourteen. So you can't tell is this
• 30:30
  Speaker 1: thing one hundred thousand years old or one hundred million
• 30:32
  Speaker 1: years old or four billion years old, because you just
• 30:36
  Speaker 1: get zero. So what you got to do is measure
• 30:38
  Speaker 1: the carbon fourteen to carbon twelve ratio in your thing,
• 30:42
  Speaker 1: and then you can extrapolate back to when did this
• 30:45
  Speaker 1: thing last have the sort of normal rate of carbon fourteen?
• 30:49
  Speaker 1: Got it all right, So dinosaurs are out, but helpful
• 30:52
  Speaker 1: for things like human archaeology questions exactly. Human archaeology was
• 30:58
  Speaker 1: really like revolutionized this subject. The first time that they
• 31:02
  Speaker 1: used it was actually to date some Egyptian tombs. These
• 31:05
  Speaker 1: are some things that archaeologically we already knew what the
• 31:08
  Speaker 1: dates were based on writing and other analysis, Like archaeologists
• 31:12
  Speaker 1: already knew when somebody had been buried, and now they
• 31:15
  Speaker 1: were able to take a sample and measure the carbon
• 31:18
  Speaker 1: fourteen fraction in like a piece of linen or in
• 31:20
  Speaker 1: a piece of wood from the tomb and independently establish
• 31:25
  Speaker 1: the date of the death of that object, like here's
• 31:28
  Speaker 1: when the tree that formed this plank must have been killed,
• 31:32
  Speaker 1: or here's when this plant was harvested to make this linen.
• 31:35
  Speaker 1: And that's really powerful. It's like a completely separate clock
• 31:39
  Speaker 1: that lines up archaeologically with your records. Okay, So one,
• 31:43
  Speaker 1: that's awesome, and two I bet this has been used
• 31:45
  Speaker 1: at some point in ways that have made people angry,
• 31:48
  Speaker 1: like people who thought they had a thing that was
• 31:50
  Speaker 1: old but it ended up not being that old, or
• 31:52
  Speaker 1: the other way around. But before I ask you about that,
• 31:56
  Speaker 1: let's take another quick break. All right, So has this
• 32:13
  Speaker 1: method been used in a way that ended up making
• 32:16
  Speaker 1: people like why do I feel like you're digging for
• 32:21
  Speaker 1: the controversy here? Keey? Well, you know it makes good radio.
• 32:25
  Speaker 1: It does absolutely. Yeah, this is a really cool technique
• 32:28
  Speaker 1: and it's powerful because they can date things to like
• 32:30
  Speaker 1: within a few decades. You know. The thing is that
• 32:33
  Speaker 1: there's a lot of carbon in living stuff, and the
• 32:36
  Speaker 1: more carbon you have, the more preciser measurement can be.
• 32:39
  Speaker 1: So you can like pin down to within a few
• 32:41
  Speaker 1: decades when something died, and for example, when people discovered,
• 32:45
  Speaker 1: like the Dead Sea Scrolls, these ancient scrolls outside of
• 32:48
  Speaker 1: Jerusalem that have been in the desert for who knows
• 32:51
  Speaker 1: how long, and what may have been one of the
• 32:52
  Speaker 1: earliest written records of you know, the books of the Bible.
• 32:56
  Speaker 1: People wanted to know like, are these real? Are they
• 32:59
  Speaker 1: actually thousands of years old? Or is this like a
• 33:01
  Speaker 1: forgery from last week that's been stained with tea? And
• 33:06
  Speaker 1: so they were able to use radiocarbon dating to confirm
• 33:09
  Speaker 1: that these things were one thousand, nine hundred and seventeen
• 33:12
  Speaker 1: years old, which really told people like, these are an
• 33:15
  Speaker 1: ancient relic. You know, these are not created recently, or
• 33:18
  Speaker 1: at least the materials on which they were made are
• 33:21
  Speaker 1: fairly old. So either it's a really old book or
• 33:24
  Speaker 1: it's new writing on a really old sheet of paper. Well,
• 33:27
  Speaker 1: I'm gonna have to give you that. That's awesome. That's
• 33:29
  Speaker 1: not what I asked. I asked you for controversy that
• 33:32
  Speaker 1: you gave me confirmation. But still all right, so that's
• 33:35
  Speaker 1: pretty awesome. Well this controversy. Also, you may have heard
• 33:39
  Speaker 1: about the Shroud of Turin. This is this piece of
• 33:41
  Speaker 1: cloth that I think is held in Milan. That's supposed
• 33:44
  Speaker 1: to have like the face of Jesus on it, and
• 33:47
  Speaker 1: the mythology around it is that it wrapped to Jesus's
• 33:50
  Speaker 1: corpse and was sort of imprinted by the power of
• 33:53
  Speaker 1: his un don't know, spiritual personality with his face. And
• 33:57
  Speaker 1: so this is a relic that's been celebrated in people
• 34:00
  Speaker 1: like pilgrimage to go and see it, and so they
• 34:03
  Speaker 1: radiocarbon dated it and discovered Oops, it's actually from the
• 34:06
  Speaker 1: fourteenth century, which means it's pretty old. It's like six
• 34:10
  Speaker 1: hundred years old. But the plants that made this shroud
• 34:14
  Speaker 1: were grown and planted like fourteen hundred years after Jesus died.
• 34:18
  Speaker 1: That's disappointing. Is it safe to assume that there are
• 34:22
  Speaker 1: people who don't buy the science on this to this day? Oh? Absolutely,
• 34:26
  Speaker 1: the way people deny evolution or that the Earth is
• 34:29
  Speaker 1: round or the dinosaurs existed well before humans. There are
• 34:33
  Speaker 1: people who say radiocarbon dating is not reliable and that
• 34:36
  Speaker 1: you can't use it, especially, you know, when it contradicts
• 34:39
  Speaker 1: their belief. The thing I love about the Shroud of
• 34:42
  Speaker 1: Tern story is not just that it reveals that the
• 34:45
  Speaker 1: whole thing is a hoax, but it's an ancient hoax.
• 34:48
  Speaker 1: The hoax is now hundreds of years old, right, the
• 34:51
  Speaker 1: hoax itself is of historical interest. That's how old it is. Right,
• 34:56
  Speaker 1: A six hundred year old hoax is pretty cool. Okay,
• 34:59
  Speaker 1: it's not the face of g but wow, that's really
• 35:01
  Speaker 1: cool insight and like what people were doing and why
• 35:03
  Speaker 1: they wanted to do it and all sorts of stuff.
• 35:05
  Speaker 1: I love how like today's mundanity, right, and even lies
• 35:08
  Speaker 1: can turn into something fascinating for future anthropologists. Yeah, know,
• 35:13
  Speaker 1: humans have enjoyed messing with each other for a really
• 35:16
  Speaker 1: long time. It's good to know that. But it is
• 35:19
  Speaker 1: tricky to date things with carbon fourteen because it turns
• 35:22
  Speaker 1: out that the assumption we made at the beginning that
• 35:24
  Speaker 1: like carbon fourteen is produced in the upper atmosphere and
• 35:27
  Speaker 1: spreads around mostly evenly to everything, it's not exactly true,
• 35:32
  Speaker 1: and so you got to like make some corrections and
• 35:35
  Speaker 1: calibrations to get things as precise as you'd like. So, like,
• 35:38
  Speaker 1: how not exact are we talking here? Like you know
• 35:43
  Speaker 1: the flies that you find in bodies? I think things
• 35:45
  Speaker 1: like temperature impact development time. How many things impact our
• 35:49
  Speaker 1: ability to date things based on carbon fourteen? And are
• 35:52
  Speaker 1: they things that we can learn about and control for
• 35:55
  Speaker 1: or no, yes, absolutely we can learn about them. And
• 35:57
  Speaker 1: it's like a whole field of people calib rating carbon
• 36:00
  Speaker 1: fourteen dating. We first discovered this actually when carbon fourteen
• 36:04
  Speaker 1: dating got some Egyptian tombs wrong, like some of them
• 36:08
  Speaker 1: were bang on the archaeological records, and other ones that
• 36:11
  Speaker 1: archaeologists were pretty sure about. Radiocarbon dating got a little wrong,
• 36:15
  Speaker 1: and people thought, hmm, that's weird. I wonder what it means.
• 36:18
  Speaker 1: And so they discovered a few interesting effects. For example,
• 36:21
  Speaker 1: carbon fourteen production is not constant over time. If you
• 36:25
  Speaker 1: want to assume that you can extrapolate backwards from the
• 36:27
  Speaker 1: carbon fourteen ratio today to the carbon fourteen ratio when
• 36:31
  Speaker 1: this object died, you have to assume the carbon fourteen
• 36:34
  Speaker 1: is being replenished at the same rate over time. But
• 36:36
  Speaker 1: it turns out that it's not that there's a variation
• 36:40
  Speaker 1: in the carbon fourteen rates in the atmosphere. Whoa is
• 36:44
  Speaker 1: that because cosmic rays hit us at different rates? Is
• 36:47
  Speaker 1: this like a solar Now that's not a solar wind thing?
• 36:50
  Speaker 1: Do we know? Yeah? Why? I am confused. It's really
• 36:54
  Speaker 1: interesting and there's some cool physics there. One is that, yes,
• 36:57
  Speaker 1: cosmic rays have sort of like seasons that are not
• 37:00
  Speaker 1: holy constant. It's sort of like the solar weather. You know,
• 37:03
  Speaker 1: where these cosmic grays come from depend on like magnetic
• 37:06
  Speaker 1: fields and the galaxy. You know, what's going on with
• 37:09
  Speaker 1: the objects that are created them. So there's those kinds
• 37:12
  Speaker 1: of effects. But we can actually measure that in independent
• 37:15
  Speaker 1: ways because they can look at super ancient trees, right.
• 37:20
  Speaker 1: Trees are really cool because they grow and they add rings,
• 37:24
  Speaker 1: and those new rings interact with the biosphere, but the
• 37:26
  Speaker 1: old rings don't. So every year a tree is basically
• 37:31
  Speaker 1: like taking a sample of the carbon fourteen fraction in
• 37:34
  Speaker 1: the atmosphere and storing it forever. And so if you
• 37:37
  Speaker 1: slice open a really old tree and look back at
• 37:40
  Speaker 1: the carbon fourteen fraction in each of the rings, you
• 37:43
  Speaker 1: can get like a history of the carbon fourteen fraction
• 37:46
  Speaker 1: at the time that the tree was growing. Do you
• 37:48
  Speaker 1: not happen to know what the oldest tree we've done
• 37:50
  Speaker 1: that on is. Are we talking about like hundreds of
• 37:53
  Speaker 1: years worth of data? A thousands. We have lots that
• 37:55
  Speaker 1: are hundreds of years and a few that are thousands
• 37:58
  Speaker 1: of years, and so that really helped us calibrate like
• 38:00
  Speaker 1: the more recent fluctuations in carbon fourteen. But also humans
• 38:05
  Speaker 1: have really altered the carbon fourteen fraction in the atmosphere.
• 38:09
  Speaker 1: For example, we've been burning a lot of fossil fuels
• 38:12
  Speaker 1: over the last couple of hundred years. Fossil fuels have
• 38:15
  Speaker 1: carbon but no carbon fourteen, so we've been releasing a
• 38:19
  Speaker 1: lot of carbon twelve into the atmosphere, really bringing down
• 38:22
  Speaker 1: the carbon fourteen fraction in the atmosphere. So, like, human
• 38:26
  Speaker 1: effects have really changed this and made it more complicated
• 38:29
  Speaker 1: to interpret the past. Wow. So like if you were
• 38:32
  Speaker 1: an alien trying to age stuff that was happening down
• 38:35
  Speaker 1: here on Earth, and you wanted to age something you know,
• 38:38
  Speaker 1: thousands of years from now that happened during our period,
• 38:42
  Speaker 1: it would be a mess. It would be a mess
• 38:44
  Speaker 1: if you didn't have ways to calibrate it. And so fortunately,
• 38:47
  Speaker 1: like trees can help us understand these things. Because trees
• 38:50
  Speaker 1: have been around for hundreds of years since, we can
• 38:52
  Speaker 1: understand the effect the humans have had on the carbon
• 38:55
  Speaker 1: fourteen fraction in the atmosphere. But more confusingly, we've had
• 38:59
  Speaker 1: effects in both directions. So burning fossil fuels lowers the
• 39:03
  Speaker 1: carbon fourteen fraction because you're pumping out super old carbon
• 39:06
  Speaker 1: where everything has already decayed. But nuclear testing in the
• 39:09
  Speaker 1: atmosphere increases the carbon fourteen fraction because it makes new
• 39:13
  Speaker 1: carbon fourteen. Is all this radiation and all the products
• 39:16
  Speaker 1: of the nuclear testing makes lots and lots of carbon fourteen,
• 39:20
  Speaker 1: much more than it's made from cosmic rays. So like
• 39:23
  Speaker 1: in the middle of this century, we had like twice
• 39:25
  Speaker 1: as much carbon fourteen in the atmosphere as we usually do.
• 39:28
  Speaker 1: Where the worst that'll be another interesting problem for the
• 39:33
  Speaker 1: aliens to solve. Then where did all this carbon fourteen
• 39:36
  Speaker 1: come from? Oh, they were setting off nuclear weapons in
• 39:38
  Speaker 1: the sky, of course there were. It's fascinating because there's
• 39:42
  Speaker 1: two sides to that. Archaeologists are frustrated by that because
• 39:45
  Speaker 1: we're like poisoning the historical record and making it harder
• 39:48
  Speaker 1: to figure out when things came from. But geologists actually
• 39:52
  Speaker 1: really like it because it's like a really bright signal.
• 39:55
  Speaker 1: They're like, Okay, cool, we can use this to calibrate
• 39:57
  Speaker 1: and we can tell when something happened because the so
• 40:00
  Speaker 1: much carbon fourteen in that layer. So geologists, I think
• 40:03
  Speaker 1: would like us to be like regularly nuking the atmosphere
• 40:05
  Speaker 1: in predictable and periodic ways because it leaves like this
• 40:10
  Speaker 1: ruler back in the record. You know, I know a
• 40:12
  Speaker 1: geologist I think is not quite that self interested, but
• 40:16
  Speaker 1: I can imagine him thinking that that's a silver lining
• 40:19
  Speaker 1: of an awful thing. Humans are complicated. So yeah, so
• 40:22
  Speaker 1: you have to take all this into account, and you
• 40:24
  Speaker 1: have to know, like what was the rate of carbon
• 40:26
  Speaker 1: fourteen in the atmosphere over the last few thousand years.
• 40:29
  Speaker 1: And you also have to take into account where you
• 40:31
  Speaker 1: have found something. If you found it in the deep ocean,
• 40:34
  Speaker 1: then it was going to get less carbon fourteen to
• 40:36
  Speaker 1: begin with, and then if you found it in the
• 40:38
  Speaker 1: upper atmosphere. Also, the different hemispheres of Earth have different
• 40:42
  Speaker 1: depositions of carbon fourteen because there's different like patterns of winds,
• 40:46
  Speaker 1: and the North and the South hemisphere actually have totally separate,
• 40:50
  Speaker 1: independent wind systems that don't really mix very well. So
• 40:53
  Speaker 1: there's less carbon fourteen in the southern atmosphere because it's
• 40:56
  Speaker 1: like more surface area of ocean which sucks up more
• 41:00
  Speaker 1: carbon fourteen, and there's more carbon fourteen in the northern
• 41:02
  Speaker 1: hemisphere where this is less ocean surface. Do you have
• 41:06
  Speaker 1: any sense for like for the hemisphere thing, are we
• 41:08
  Speaker 1: talking like if you didn't correct for that, you'd be
• 41:11
  Speaker 1: off by about ten years or a thousand years, or
• 41:14
  Speaker 1: it just kind of depends on a lot of other
• 41:15
  Speaker 1: stuff too. These all are really small effects, and everybody
• 41:18
  Speaker 1: wants really precise dating of things, you know, down to
• 41:21
  Speaker 1: the decades, and so this is the kind of thing
• 41:23
  Speaker 1: that happens in science. First, you have a very approximate effect.
• 41:26
  Speaker 1: You're like, okay, let's just assume carbon fourteen is constant
• 41:29
  Speaker 1: everywhere and over time. What do we get? Oh my gosh,
• 41:32
  Speaker 1: it can teach us something already. Then you start to
• 41:35
  Speaker 1: hone in on the details you want, like the second
• 41:37
  Speaker 1: digit to be accurate, and then the third, and then
• 41:39
  Speaker 1: the fourth, and by now we're like, you know, seventy
• 41:42
  Speaker 1: years into this research project, we're getting down to the
• 41:45
  Speaker 1: nitty greedy details. So a lot of these things will
• 41:47
  Speaker 1: affect our estimate for the dates of things by decades
• 41:51
  Speaker 1: or maybe up to hundreds of years, not thousands of years.
• 41:54
  Speaker 1: It's not going to like up end everything we thought
• 41:57
  Speaker 1: we knew. We also need a really precise estimate of
• 42:00
  Speaker 1: the half life of carbon fourteen, right, we have to
• 42:03
  Speaker 1: be able to calibrate this clock to know how long
• 42:06
  Speaker 1: does it take carbon fourteen two decay? And as you said,
• 42:09
  Speaker 1: you can't wait around for five thousand years, which would
• 42:11
  Speaker 1: be the best way to get an accurate measurement. But
• 42:13
  Speaker 1: people have been developing more and more precise experiments with
• 42:16
  Speaker 1: like larger samples of carbon fourteen, So they actually had
• 42:19
  Speaker 1: to update the official half life of carbon fourteen from
• 42:23
  Speaker 1: fifty five sixty eight later to fifty seven thirty so
• 42:27
  Speaker 1: a change of like one hundred and fifty years. And
• 42:29
  Speaker 1: this is super fascinating because it then required a change
• 42:32
  Speaker 1: of all the archaeological dates. Like all the archaeologists who
• 42:36
  Speaker 1: thought that their thing was data to a certain date. Oops,
• 42:38
  Speaker 1: they got updated because the nuclear physicists or the chemists
• 42:41
  Speaker 1: got the number wrong. Does that mean that you get
• 42:43
  Speaker 1: to redo all of your publications with the updated date
• 42:48
  Speaker 1: and double the number of lines you have on your
• 42:50
  Speaker 1: CV because in that case, thank you physicists. It means
• 42:53
  Speaker 1: that there's a bunch of papers out there with old
• 42:55
  Speaker 1: dates that we now like no need corrections. You can't
• 42:58
  Speaker 1: just read the old pay in archaeology and take the
• 43:01
  Speaker 1: dates and face value. You have to know when that
• 43:03
  Speaker 1: date was calculated. Like what effects did they take into account?
• 43:07
  Speaker 1: And what effects do we now take into account? So
• 43:10
  Speaker 1: the whole thing has gotten really really complicated. That is frustrating,
• 43:13
  Speaker 1: but it also has been an enormous boon to archaeology.
• 43:17
  Speaker 1: I mean, what a powerful tool, Like anything that was alive,
• 43:20
  Speaker 1: now you can date the moment of its death. And
• 43:23
  Speaker 1: that's not a perfect tool, right, It still thinks like
• 43:26
  Speaker 1: when was this metal forged? Well, we can't tell because
• 43:28
  Speaker 1: it was never alive. It doesn't participate in the carbon biosphere,
• 43:32
  Speaker 1: So you can't date like jewelry, you know, or swords
• 43:35
  Speaker 1: or stuff like that, but you can look at what
• 43:37
  Speaker 1: else is in a grave and you can tell maybe
• 43:39
  Speaker 1: when that person died. And before this, archaeologists had much
• 43:43
  Speaker 1: more rudimentary methods. You know, they had this like layer
• 43:46
  Speaker 1: method where they would like count down from the ground
• 43:49
  Speaker 1: and try to like find things that they knew happened
• 43:52
  Speaker 1: that they could use to like sandwich when their relics
• 43:55
  Speaker 1: might have been buried. So it was very, very rough.
• 43:58
  Speaker 1: And now we have this whittle measure for these objects
• 44:01
  Speaker 1: when they died. It's super powerful. It's super powerful. But
• 44:05
  Speaker 1: I wonder if there was also a generation of scientists
• 44:07
  Speaker 1: who are like, you know, the whole reason I got
• 44:09
  Speaker 1: into archaeologies because I don't want to be in the lab,
• 44:12
  Speaker 1: and now I have to be in the lab to
• 44:14
  Speaker 1: get these dates. But on the other hand, I think
• 44:17
  Speaker 1: we all benefit when we get to more accurate, precise information. Yeah,
• 44:21
  Speaker 1: I think that's probably true. After this was discovered, very rapidly,
• 44:24
  Speaker 1: a bunch of labs were set up around the world
• 44:26
  Speaker 1: to start doing radiocarbon dating. So it's not the kind
• 44:29
  Speaker 1: of thing that like a typical archaeologist so does in
• 44:32
  Speaker 1: the field, or every archaeologist has their own radiocarbon setup.
• 44:36
  Speaker 1: It's a little bit of an involved process. What you
• 44:38
  Speaker 1: have to do is measure the carbon fourteen ratio. In
• 44:41
  Speaker 1: the old days, what they did was just sort of
• 44:42
  Speaker 1: like count the radiation emitted because it's emitting beta rays
• 44:46
  Speaker 1: when it's decaying. So that was the old strategy. More
• 44:49
  Speaker 1: recently they have a more precise strategy which uses mass spectrometer.
• 44:53
  Speaker 1: So it takes a sample of it, accelerates it bends
• 44:56
  Speaker 1: it through a magnetic field, and then it'll bend more
• 44:59
  Speaker 1: if it has low mass ass unless if it has
• 45:01
  Speaker 1: high mass. So it gives you like a spectrum of
• 45:03
  Speaker 1: the mass of the object that you're sampling, and you
• 45:06
  Speaker 1: can tell how much carbon fourteen, how much carbon twelve
• 45:09
  Speaker 1: is in there. You don't have to wait for the
• 45:11
  Speaker 1: carbon fourteen to decay, so you're getting to take advantage
• 45:14
  Speaker 1: of all the carbon fourteen in there, not just the
• 45:17
  Speaker 1: ones that happen to be decaying as you're watching. So
• 45:20
  Speaker 1: these are pretty specialized techniques now, and I think most
• 45:23
  Speaker 1: archaeologists like will send a sample to the lab rather
• 45:26
  Speaker 1: than like doing it themselves. So I think you still
• 45:28
  Speaker 1: have like old school Indiana Jones types out there in
• 45:31
  Speaker 1: the field, gathering stuff, plundering sites, civilization exactly. Oh man,
• 45:37
  Speaker 1: the ethics of archaeology not something I want to get into. Yeah,
• 45:40
  Speaker 1: nuralistic was science, Yeah, but then sending those samples to
• 45:43
  Speaker 1: a lab to do the dating. So you probably have
• 45:46
  Speaker 1: like a division. You know, you have the radiocarbon archaeologists
• 45:49
  Speaker 1: in the lab and the folks who are not in
• 45:51
  Speaker 1: the lab. Okay, well, let's step away from the ethical
• 45:54
  Speaker 1: quandaries presented to us by archaeology and talk about dinosaurs.
• 45:59
  Speaker 1: So sorry, So we've we've established, unfortunately early on, that
• 46:03
  Speaker 1: carbon fourteen is not help for dinosaurs. Is there something
• 46:06
  Speaker 1: we can use if we're interested in when a dinosaur bone,
• 46:10
  Speaker 1: you know, when the dinosaur died. Dinosaurs are tricky, absolutely,
• 46:14
  Speaker 1: because this clock has all run out. All carbon fourteen
• 46:17
  Speaker 1: that was in dinosaurs has now decayed. So what you
• 46:20
  Speaker 1: need are longer clocks. We did an episode about using
• 46:24
  Speaker 1: uranium to date stuff because there's this cool relationship between
• 46:28
  Speaker 1: uranium and lead. Uranium two thirty eight and uranium two
• 46:32
  Speaker 1: thirty five has half lives of more than a million years,
• 46:35
  Speaker 1: and so they're useful for dating stuff that's super duper old.
• 46:38
  Speaker 1: And when they form, this cool thing happens. They get
• 46:41
  Speaker 1: these zircon crystals zi r c N, And when those
• 46:45
  Speaker 1: zircon crystals form, they reject any lead and they like
• 46:48
  Speaker 1: expel lead from inside the crystal. So when they're formed,
• 46:52
  Speaker 1: they're like lead free, but they do take uranium in them,
• 46:56
  Speaker 1: and uranium decays into lead, so each one is like
• 46:59
  Speaker 1: a little hawk. Could you pick up a zircon crystal
• 47:01
  Speaker 1: and measure how much lead is inside of it, you
• 47:04
  Speaker 1: can tell when it was formed. So now we're dating
• 47:07
  Speaker 1: like when a rock cooled into these crystals, which is
• 47:11
  Speaker 1: pretty cool. That's awesome, And so then you measure in
• 47:14
  Speaker 1: the rock around the fossils or something. Yeah, exactly. Now,
• 47:17
  Speaker 1: dinosaur bones don't have this stuff in them, but sometimes
• 47:21
  Speaker 1: around the dinosaur bones there's like cooled magma, so this
• 47:25
  Speaker 1: igneous rock. Because fossils only form in sedimentary rock. But
• 47:29
  Speaker 1: if you have like layers of igneous rock above and
• 47:32
  Speaker 1: below your fossil, then you can use the zircon crystals
• 47:35
  Speaker 1: in those rocks to figure out when those crystals were
• 47:38
  Speaker 1: formed and therefore racket your dinosaur bones, so you can
• 47:41
  Speaker 1: tell roughly when it must have existed. Yea science. Science.
• 47:46
  Speaker 1: I was always puzzled as a kid when people would
• 47:48
  Speaker 1: talk about like the age of rocks. I'm like, what
• 47:50
  Speaker 1: does that mean? Like when is a rock born? Right,
• 47:53
  Speaker 1: it's not. Rock was never alive. And there's only later
• 47:55
  Speaker 1: that I understood that they're talking about when the rock cooled.
• 47:58
  Speaker 1: Because you have like that block of magma. It was
• 48:01
  Speaker 1: still basically rock. It was just like liquid rock. But
• 48:03
  Speaker 1: it's when it's cooled into a rock and formed crystal.
• 48:06
  Speaker 1: That's what they're interested in. That's what they're measuring. It's
• 48:09
  Speaker 1: like saying, how old is my ice cube? Well, you know,
• 48:12
  Speaker 1: the water in it has been water forever, but it's
• 48:14
  Speaker 1: only been an ice cube since you put it in
• 48:16
  Speaker 1: the freezer last Tuesday. So that's like the age of
• 48:19
  Speaker 1: your ice cube in the same way. It's a good
• 48:20
  Speaker 1: way to explain it. So yeah, that's the story of
• 48:23
  Speaker 1: radiocarbon dating, this incredible cool process where clocks are created
• 48:27
  Speaker 1: in the upper atmosphere and then drift down into the
• 48:30
  Speaker 1: biosphere inhaled by plants eaten by you and then stop
• 48:34
  Speaker 1: ticking and as soon as you stop eating and breathing.
• 48:38
  Speaker 1: Thanks very much Kelly for joining us on this trip
• 48:40
  Speaker 1: into debunking the Shroud of Turn and confirming the Dead
• 48:44
  Speaker 1: Sea scrolls. Thanks for bringing me along up the trip.
• 48:46
  Speaker 1: I had a great time, all right, and thanks everyone
• 48:49
  Speaker 1: for listening, And if you have questions about how something works,
• 48:52
  Speaker 1: please don't be shy, right to us to questions at
• 48:54
  Speaker 1: Dangel and Jorge dot com. Tune in next time. Bye,
• 49:06
  Speaker 1: Thanks for listening, and remember that Daniel and Jorge Explain
• 49:09
  Speaker 1: the Universe is a production of iHeartRadio or more podcast
• 49:13
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