How Carbon-14 Dating Works

Some of the carbon dioxide in your body is radioactive! Don’t worry, it won’t harm you (not sure why we used an exclamation point there). Instead, it might someday be detected by future archaeologists to determine how long ago you walked the Earth.

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Episode Transcript

Speaker 1 (00:00):
Hey, San Francisco, we want to get back to our
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(00:22):
are we there? We're gonna be there Saturday, January. That's
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links to get information and tickets and we'll see you
guys in January. Welcome to Stuff You Should Know, a
production of My Heart Radios How Stuff Works. Hey, and

(00:46):
welcome to the podcast. I'm Josh Clark. There's Charles W.
Chuck Bryan over there. There's Jerry right there, just laughing
it up. Yeah, and this is Stuff you should Know.
The jokes are Jerry ed issue Dent Science Edition a
k a. Chuck Dies Slowly inside Edition. Dude, No, it's
not You're gonna do just fine. This is all so intuitive,

(01:09):
it's wonderful. I'm not worried about not doing fine, but
thanks for the Reachirch. Well then I'm I'm really excited
about this. If you know that, I think you're gonna
do fine. You are going to as well. I'm going
to see to it. I think Jerry's gonna do great. Jerry,
how how are you doing over there? Okay, she's pressing
buttons like I've never seen her press buttons. Stop to that. Um,

(01:31):
I wonder what kind of weird sound effects just happened
after touching all those buttons. Jerry just laughed. I don't
know if the mic pick that up. All right, everybody's like, okay,
you're officially stalling now. Jerry's a quiet laugher. Though you
ever noticed that it's all knows, Yeah, she's all knows.
This is Jerry laughing hard. There's some doing it right now.

(01:56):
Serious a SMR triggering going on right now, that's right.
And there's of this not on the microphone cover, all right,
Carbon fourteen dating It works sort of the end. It's
not the worst description of it ever. Yeah, we can
do better than that, though, Yes, and luckily you did
a great job with this. But I also you know,
my advice to anyone if you don't understand the science thing,

(02:19):
and you're an adult, just don't worry about what anyone
behind you thinks. Just looking at your laptop and you
go to the most rudimentary children's science website you can find,
and that always helps. There is no shame in that,
no shame because seriously, the people who write those websites
are probably some of the best science explainers on the
planet and they know how to really just not dumb

(02:40):
it down because kids are smart. But that's funny. You
flip flopped on kids. Apparently you mean stupid kids. Yeah,
you always said they were dumb until just now, So
good for you, Chuck. We're all over the map. Well,
I feel like we're really growing up these days. So
so Carbon four Team, for those of you who don't know,
is this um really clever scientific method where you can

(03:04):
actually kind of look inside of a material and figure
out how much carbon fourteen is in there, and by
doing so, you can actually tell how old it is,
or at least how long ago it was since the
thing you're dating was alive. Yes, and it is a
comparative Well, there's another word for that. What's it called

(03:25):
relative dating? Yeah, relative dating, I guess comparative isn't the
worst word, especially if you're talking about literature, right because
what they're doing is comparing it to things that are
alive today, and because of all the gobbledygook we're about
to talk about, that equals a pretty good estimate. And
then from there they are even further things that one

(03:46):
can do if one we're so inclined as a scientist,
and there are a lot of people who are inclined
to do this. This is a very exciting, um energetic
field of science right now, Like if you want to,
if you want to jump into an ever evolving, constantly
moving be a um field, the Baracas field kind of

(04:08):
um of of science, start studying radiocarbon dating actually wouldn't
be a ba Barakas field because didn't that stand for
bad attitude? Did it? I think so? Right? Oh, no,
one in radiocarbon dating has a bad attitude, but they
are be as right. But you're right it it is
ever evolving and they're constantly looking for better ways to

(04:29):
pinpoint more accurate timelines on things. So it's not like
a job you're going to get in and be like,
oh this whole thing again, right, No, no, And it's
it's just like they're constantly filling in blanks and stuff
like that. It's just it's good work. So, um, what
they're looking for the people who do radiocarbon dating is
carbon fourteen, which I said, and that is radiocarbon. It's

(04:51):
called that because it's a radioactive form of carbon, that's right,
And it's everywhere on Earth. It's just all over the place.
It's part of the carbon side goal and it's part
of the web of life. But it starts out way
up in outer space as cosmic ray, that's right. Should
we give the basis definition before we jump to the

(05:12):
radio carbon dat Yeah? Yeah, I mean I think like
the most rudimentary definition might help some people out. Um.
But like you said, carbon fourteen is everywhere, including inside us,
because it's in plants via photosynthesis, and we eat plants,
and animals eat plants. Some people eat animals, and because
of that, it's kind of in every living thing. Uh.

(05:35):
And carbon fourteen dies away very slowly. And because we
know this, because we know it happens predictably, then we
can measure that in a sample and then compare it,
like I said, to something living and then you do
a little math Ipso fact though it's probably an ipso
facto is it? Presto change, Yeah, presto change about it

(05:59):
being about about it being bon Jovi? What was that
that was yours? Was it? Yeah? Man? You came up
with that on a carousel at Zoo Atlanta in about
two thousand and twelve. That's right. That's where that's carbon
dated too. Yeah, that joke. But because we know that,
we can compare it to something that's alive today and

(06:20):
then with a little math we can figure out the
rough estimate of how old it is. Yeah, that's I mean,
that's radio carbon dating in a nutshell for sure. That's right.
But like you said, it starts out as cosmic rays
way out in outer space, right, and so a cosmic ray,
we're not entirely certain where they come from, but they're
super high energy particles, usually like pieces of atoms, that

(06:42):
are just shooting towards Earth and through outer space at
incredible speeds, and when they encounter the atmosphere, they start
running into the atoms that make up the atmosphere. And
because these particles are so high energy, these cosmic rays,
when they smack into atoms and other particles in all
acules and all that. They just burst them apart, not

(07:03):
just burst like an adam into like it's protons and neutrons.
It'll tear apart of neutron like like it's nothing. Actually
creates other high energy particles like muons, pions, x rays, um,
what else? Zaxon's No, that was a video game, was it, Zaxon? Yeah?

(07:27):
With a z uh Yeah. I think it was z
A double x O N. I am not familiar with that. Okay,
it wasn't a stand up game. Actually it may have been,
but I played it on a r because I could
see a kid in a Kiss T shirt playing that
game stand up in an arcade. Yes, it sounds like
that kind of game. That would have been me had
I not been deathly afraid of Kiss because they were devil.

(07:51):
They were nights in Satan's service obviously. Yeah. Okay, So
all these muons, X rays, pions, all that stuff, there's
one other little particle that can be created when a
cosmic ray collides with an atom, and that is a neutron,
a high energy neutron. Right, that's right. Okay, So what's
happening now is a chain reaction because cosmic rays are

(08:14):
bombarding the atmosphere, that's right, And uh, what can happen
is they can get really pushy. Uh if a high
energy neutron collides with let's say a nitrogen fourteen atom, Yeah,
they'll get real pushy and they'll just knock the proton
off and move right in there and say this is
my house now, right. So what was once a stable
atom nitrogen fourteen, which had seven protons and seven neutron,

(08:41):
is now an unstable atom with six protons and eight neutrons,
and now it's no longer nitrogen fourteen. What you have, fella,
is carbon fourteen. Yes, an unstable meaning radioactive, but not
radioactive meaning like scary and dangerous. No, it just means it.
It's it's in a higher energy state, and it's temporary.

(09:03):
Eventually wants to decay back into that um nitrogen fourteen stately, Yeah,
eventually it's sometimes spontaneously, sometime down the road, that neutron
will turn back into a proton, which sounds like magic
until you realize that atoms and all of the particles

(09:24):
that make up atoms are really just vibrations of energy,
and it can temporarily go to a higher energy state
or a lower energy state. And that is how something
would change from like a high energy neutron back to
a proton. Right. And he said that carbon fourteen is everywhere,
which is true, but that doesn't mean there's like tons
and tons of it relative to carbon carbon twelve. Yeah,

(09:48):
there's a lot more carbon twelve. Right. So carbon twelve
is the stable version of carbon, and it's way more
abundant than carbon fourteen. Carbon fourteen is kind of like
a freak, a monster that gets made accidentally, and it's
extremely rare, even though there's a ton of it, but
compared to carbon twelve, it's very rare. Something like one
carbon fourteen atom for every trillion carbon atoms. That's that's

(10:15):
that's pretty rare. But it also gives us a ratio chuck,
And this is a big initial point. Yeah, And like
you mentioned before too, or maybe I said it, it's uh,
this is part of the carbon cycle. So it's inside
all the plants and the animals. Reading the plants were
eating plants, some people eat animals, so it's inside all
of us and it's everywhere. Uh. But that ratio is

(10:37):
really important because, like we said, it starts to decrease
because it craves homeostasis and wants to get back to
its former life. It's a stable particles, a stable boy,
stable boy, brush that horse, and it would be it
would be an atom because it's going from a carbon
fourteen atom to a nitrogen fourteen atom, right, But that

(10:59):
ratio is in ard it because as it's you know,
dies away, they're going to be fewer and fewer carbon
fourteen atoms with that dead organism over time, whereas if
something is alive, it has that steady amount. And that's
where the comparison comes in, right, because as far as
a plant, or you, or a dog or anything living

(11:21):
is concerned, there's no difference whatsoever between a carbon fourteen
molecule of carbon dioxide and a carbon twelve molecule of
carbon dioxide. Yeah. I mean, it sounds hard to digest
because we said it's radioactive, but there really is no
difference as far as we're concerned, right. Um, It basically
takes a human scientists to analyze it using an extremely

(11:43):
sophisticated machine to be able to tell the difference. So
that means that when it does, you know, come down
out of the atmosphere, it's spewed out by a volcano
or something like that. Um that it just becomes part
of the food chain like any other atom of part
of carbon that's locked in with oxygen to form carbon dioxide.
So as you're living, like you were saying, you're constantly

(12:07):
taking it in, you're constantly eating. It's just a part
of life, as carbon fourteen and carbon twelve. Right, But
when you die, you stop taking in carbon of all kinds,
and all of a sudden that a clock has said
because of that decay of carbon fourteen, that's right, And
that decay, like we said, it happens spontaneously, and Adam

(12:28):
might suddenly convert from carbon fourteen to nitrogen fourteen. You
can't predict when that's going to happen because of the uncertainty.
That's part of quantum physics, right, But if you have
a large enough sample, then you can start to predict
when x number or x percentage of that that sample

(12:48):
of carbon fourteen will have spontaneously changed from carbon fourteen
to nitrogen fourteen. And that's called the half life. That
which is everyone has heard of. That's that's half life.
It's just standard stuff. Yeah, I think everyone has heard
of half life, and about the people that know that
term don't really fully grasp it. Well, yeah, it's just

(13:09):
this the amount of time it takes for half of
the radioactive atoms in any given sample to convert back
into a stable form. Yeah, that's it. It's pretty easy. Uh.
And we know in this case the half life and
we'll get to how we figured all this out, but
the half life of carbon fourteen is five thousand, seven

(13:29):
hundred and thirty years. Um, if you know you keep going,
it goes to a quarter life, then I guess in eight. Yeah,
it just keeps going. So like if you have a
hundred carbon fourteen atoms, if you come visit it in
fifty and thirty years, you're gonna find you a fifty.
And if you visit in another thirty years, you're going

(13:51):
to have then twelve and a half or thirteen maybe,
I don't know. It just keeps going until there's ultimately none.
Laughed over a long enought touch of time, which is
with carbon fourteen, like fifty or sixty thousand years. Yeah,
I saw sixty thousand mostly, but then I think it
starts can get a little hinky at fifty, So fifty

(14:11):
to sixty is pretty good, and I think it gets
hinky at this point because our because of the equipment
we're using to measure it. I think as our equipment
gets more and more sensitive, that time will go further
and further out, because as long as you have two atoms,
you should still be able to measure them, you know,
for sure, or even one. Probably, I'm not going to

(14:32):
go out on a limb for that one, but I'm gonna.
I'm gonna caveat that with them probably. Okay, Well, let's
take a little break here and we're gonna come back
here in a second. Talk about the very smart dude
who figured all this stuff out quite a few years ago.

(15:00):
All right, Chuck, Just to recap real quick, because I
think this this episode bears it. Okay, Okay, you've got
carbon fourteen. It's part of the food chain. You take
it in as you're living. When you die, you stop
taking it in, and so those carbon fourteen adams start
to decay, which means that if you compared a dead
organism to a living organism, and the ratio of carbon

(15:22):
fourteen to carbon twelve in the dead organism compared to
the living organism, you be able to tell how long
ago the dead organism was alive and taking him more carbon.
And that's the basis of radio carbon dating. That's right.
So that is Uh, we have Amanda thank from the
University of Chicago name Willard Libby. That's a great name.

(15:43):
I heard his name was wild Man or wild Bill,
wild Man, Willard Libby, Yeah, because he's just crazy. I
guess you must have been a party animal. Who knows.
You don't get a nickname like wild Bill for nothing.
They don't go around handing those out to just anybody. Yeah,
not even just figuring out carbon fourteen dating. You wouldn't

(16:05):
get a wild man for that. No, No, like even
Chris Farley wasn't called wild Bill. I think Lillard Livy
had a side a side gig. Yeah, you know, but
he was the party monster maybe at the University of
Chicago in the nineteen forties. Perhaps, so he figured out
how carbon fourteen worked and how it could be used

(16:27):
to do this before we were even positive science even
knew for a fact that there was such a thing
as carbon fourteen. That's a pretty impressive, uh. And in fact,
it was just a few short years after we had
discovered cosmic rays. So he was really on the leading
edge of science. You know he was a wild man, right,

(16:48):
He's like, these particles, we're not even sure they exist,
but if they do, we could figure out how to
use them to date dead organisms. And he won a
Nobel Prize in nineteen sixty for this, I think rightfully.
So in chemistry, yeah, for sure, even though as we'll see,
he got a few things wrong. And the one thing
that's kind of tough to wrap your head around here
is he and this is it just is what it

(17:13):
is at this point, I think. But he selected nineteen fifty,
the year nineteen fifty is year zero for his experimentation,
and he compared all the samples against this, and that
is still what we do today. That we didn't. We
didn't revise a lot of this stuff. It's interesting, no, Like,
they definitely are, like, okay. I think the reason why

(17:33):
is because by the time it started to start to
become sophisticated and and more refined, so many samples had
gone through that it's like, we're just gonna stick with
this for now. It's really interesting. So nineteen fifty, when
you're radio carbon dating an object, that is year zero,
So um, anytime you get a date back, which we'll
talk about it's actually saying this is how long before

(17:56):
nineteen fifty this thing was last alive? Right, and we're
not talking it just it doesn't have to be like
a plant fossil um because we said carbon is in
you know, virtually everything. So a leather belt comes from
a cow, cow ate the plant um. What else wouldn't
plant in ships a pig fabrica. We find poop, of course,

(18:19):
old poop, old old alcohol, old beer because of yeast.
There are many, many, many things obviously bodies, oats, Yeah,
our pal. Yeah, as long as whatever you are dating
was at one point alive, which means it wasn't a
rock or a mineral from birth like it's you can

(18:42):
date it. You should be able to date as long
as it's about fifty or sixty thousand years or younger. Yeah,
But there was a problem early on in this process
because you needed a lot of this material, uh to
basically destroy to find out how old it is. And
people didn't want to give up these gray eight fines,
Like they're like, I found a a skull and they're like, well,

(19:05):
can we destroy that skull to find out how old
it is? And you know they would turn around and
say no, it's my skull, right right, And then the
radio carbon researchers saying, like I was just asking to
be pleasant, give me that skull. Yeah, but then you
would say, no, it's my skull and I'm just happy
to call it old right, And WELLRD Libby would step
in and just do like a wild man pile driver

(19:25):
on the guy with this skull got the name. You
would just come in and crush people hiding maybe in
another room and back or something, just pound someone to go,
he would swarm. Um. But here's the thing. We've gotten
a lot better over time. The equipment has gotten a
lot better, more sophisticated, so we don't need that much now.

(19:46):
And people are giving up their fines because you can
have a little gram bone from the skull and I
think everything will be okay. Yeah. And so because of that,
like it's gotten way more common to radio carbon dates
stuff I read in the UK. Um they really started
dating everything they found because the UK passed a lot

(20:07):
of that said, if you're a developer and you turn
up any sort of archaeological evidence, I'm like one of
your buildings or developments, you have to pay to have
it dated. And so like it started to kind of
get the burden for paying for it was shifted to industry,
and so it started to really blow up, and that
helped kind of push the technology along and help lower
the expense and increase the sophistication of the machines that

(20:30):
were being used. Yeah, it's pretty pretty neat how that happens. Well,
here's what you gotta do if you're gonna start out
this process is you've got to really clean your sample
very well. Otherwise it's gonna um you can mess up everything,
and not just the test that you're making. If you
have what's called a hot sample, which means you didn't
clean it well enough for it's contaminated a graham of

(20:51):
hot sample, you can destroy a lab basically to the
point where they'll just have to shut down for for
weeks or even months to get everything right, and everything
in there might be destroyed, like, yeah, all the other
samples that may be super valuable my skull. Yeah, you know. Sorry. Um,
so it's a big deal if something isn't cleaned right,

(21:13):
because it really throws everything off and CARU and everything else.
But once you do have it cleaned, um, when you
date it, there's a few different methods that you can use,
but the one that I saw is the most common
is actually turning that carbon based sample into carbon graphite,
like pure carbon. And then you take that little piece

(21:33):
of pure carbon that you've just created and you shoot
a beam of energy through it, a lot of energy. Yeah,
like two million volts, which is a lot, just all
once I think they ramp it up, don't they, Yeah,
over time, but at some point it's got it's it's
been accelerated to two million volts of energy, okay. And

(21:55):
then so once you have this thing basically a particle
mini particle accelerators pass through a spectrometer which can actually
measure the different masses of the atoms in this beam
that you've shot through the graphite. That's right, it's detecting
the little bits of carbon. Yeah, that's pretty impressive stuff.
I mean, this is the kind this is the level

(22:16):
of technology we're at right now in two thousand nineteen,
and this has been around since like the eighties or nineties.
Just think of what's coming next. What do they use
Before the spectrometer, they used something beta counting, and it
was clunky and expensive and not nearly as reliable. But
basically what it did was something different where it would
sit there and and study a piece of graphite or gas.

(22:40):
They often gasify stuff to pure gas, and then it
would just like shoot a beam through and study I
think a beam. It would somehow study the sample for
days maybe, and it would count the number of atoms
that had spontaneously converted from carbon four team new carbon twelve,

(23:01):
and then it would do a little mathematic rigamarole and
say this is how this is how at this rate
of decay, this is how old this organism is. Well,
thank goodness, we have the spectrometer now then, because it's
much more precise and it sounds more futuristic too. Yeah,
mass pectrometers. So you're gonna shoot this beam, you're gonna
throw it in the Wonder machine. Actually not the Wonder machine,

(23:22):
We've already taken that. Yeah, it's a thoughtless piece of crap. Fight. Uh.
And then you compare that ratio to the again year zero,
which is the ratio in which is still a little confusing. Yeah,
it's clunky, It is very clunky. And then that difference, basically,
like we've said eight times now, shows how many years

(23:45):
have passed to produce the amount of decay in that sample. Right,
So if you took like a sample of wood from
an old ship, an old boat, you found out right,
that's the new right by the way, did you say
route yeah? Um? And you analyze and you found that
based on the amount of carbon fourteen in there, it

(24:06):
was something like, um, it dated to like eight hundred
and forty five b C E. Okay, you'd be like, great,
now we know where this ship is from. But if
you try to go out and publish a study with that,
hopefully your radio carbon colleagues would be like, whoa, whoa,
there's a few more steps involved here here, and that's
like the most precise radio carbon date anyone would have

(24:27):
ever given. You'll be laughed out of the field if
you do this instead. There's a couple of things that
you have to do first. So radio carbon dates are
given uh as a span of time, a bit of
a range, right, so it'll say. And also because it's
comparing to it's given not as a date like B

(24:49):
C E or a D or C E or anything
like that. It's BP before president years before president. So
for that piece of wood, say, you would actually get
something like twenty seven hundred and fifteen years before present
plus or minus thirty years. So is it always thirty
or is it no? No, it can can depend, it
can it can range dramatically like Leotsie is there. They

(25:14):
have them down to about three hundred or three hundred
and fifty years, And you like the shorter the span
of time, the plus or minus years or the window
of years that you get, um, the less confidence you have.
So maybe you'll have like twenty six percent confidence that
it's from you know, uh, eight hundred forty five BC

(25:38):
to eight hundred fifty five BC, but you have confidence
that there's like this two hundred year span it's somewhere
and there. That makes sense because I have a million
percent confidence that it's somewhere within the last eighteen million
years exactly exactly right. So it just keeps. The larger
the window, the more confident you are. But I mean
still you're talking a hundred two hundred years depending on

(26:00):
how old the sample is, how good the sample is,
so it's still pretty it's pretty um. They can zero
it in pretty well. And that sciences job is to
not say, well, let's just make a really big range
and that will be good enough. They want a zero
and as much as possible, Like you know, that's and
still be accurate. So the thing is, though, is if

(26:21):
you do the if you do the math, and you say, well,
wait a minute, your example, Yeah, fifteen years before present
plus or minus thirty years gives you a range of
between seven hundred and twenty six and six sixty six BC.
But that's not even close to what you said, yeah,
which was before right, Yeah, so why wouldn't be in

(26:42):
the sample? Chuck? Because uh, like we said in the
very first sentence, radio carbon dating is uh not super
I mean, it's accurate on a wide range, but it's
a little clunky. It is. Part of it is because
there's actual um problems, like known problems built in to

(27:07):
the actual process of radio carbon dating and the results
that they get back. I'll put that, I'll put that pause.
I just had sounded really long in the replay, probably
so I felt like it. But yeah, let's take a break, man,
all right, We'll come right back and talk about more
science right after this. So I thought this was was

(27:38):
this from how stuff works and you in your brain
and yeah and a bunch of other places too, and
you in your brain. Okay, but there there's an interesting
thing to note here, which is science makes a lot
of assumptions when it comes to dating stuff. Uh, and
this is the best way to say it. If you find,
like if they find like a leather shield that they

(28:00):
dig out of an archaeological site, they get super excited
and they can date the shield and they can say,
or they probably will say, well, whoever this heroic person
was in the battlefield died on this around this date,
because that's where the shield was dated from. But that
is not necessarily true because they're dating the shield from

(28:22):
the cow skin that's on the handle, let's say, and
that just says when that cow is alive. Lass has
nothing to do with when this person made the shield.
How long that leather had been around before they went
out onto the battlefield and took an arrow to the forehead. Yeah,
maybe they were like super into vintage leather to use
on their shield handle here. It's it's sounds ridiculous, but

(28:44):
it's also possible. But the thing is is archaeological or
archaeology is based on making assumptions and presumptions based on
the context. And it's like, this is totally fine, this
is widely accepted. This is not new or scandalous at all,
but like that is part of archaeology's job. As you say,
here's the context of this find. And based on this

(29:05):
radiocarbon date of this, it's a pretty good guess that
they killed the cow, made the leather, made the shield,
and the guy died probably within a ten fifteen year window.
And I mean the idea it would be an even
weirder assumption to think that it was an ancient hipster
who collected old hold leathers. Right, check out my new
that's right. And then the other part of it too

(29:28):
is they also use it to compare to other stuff.
Like if they're in a pit filled with other um
soldiers of a certain you know, from a certain nation
or clan or whatever, um, and they knew of a
lost grade, they may have found that if it kind
of roughly correlates to the date. They were thinking, Like,
there's a lot of a lot of stuff that they
put together. They don't just say, here's what the radio

(29:49):
carbon date says, so this is what it is. That's right.
So because science does this, Libby was certainly doing this.
The wild man was doing this, and he was making
assumptions and he was and hey, we're not knocking the
guy because he want a Nobel prize for this, but
he assumed a couple of things that were not correct. Uh,
One of which was he got the half life wrong. Yeah,

(30:10):
he said the half life of carbon fourteen was five thousand,
five D sixty eight years. We actually know it's fifty
thirty like we said. And he also presumed that carbon
fourteen in the atmosphere is very steady over time and
it's something we can really depend on, being like they're

(30:31):
being a certain amount. And that's not really the case either. No,
it's not that second one is a big one. Like
the first one. You can just mess around with some
math and be like, okay, well this is the actual
half life. Well, but it's interesting. That's what we've had
to do because that's another thing we didn't go back
and change because it was all done on the basis
of right. Right. So the initial stuff, the initial dates

(30:54):
that were done when Libby invented it, were based on
a half life from right but from uh, I don't
I don't know exactly when they figured it out, but
at some point in the ensuing decades they figured out, no,
the half life is actually fifty thirty and rather than
just go back and re read um uh analyze the

(31:16):
old samples which actually may have been destroyed by this time. Uh,
they said, we're just going to stick with this convention
and follow it, and we could just do the math
and just say, actually, this is the real half life
converted to the libyhalf life, and then have a radiocarbon date. Yeah.
But the other thing he got wrong, like you said,
is is the bigger problem because it can't just be

(31:37):
solved with math, and that is his presumption that uh,
carbon fourteen in the upper atmosphere is produced at a
steady rate. We know now that they are all kinds
of things that can and have affected that rate over
the years, everything from ocean currents to super volcanoes, two
solar flares, to the Earth's magnetic field. It is fluctuated

(32:00):
a lot over time. Yeah, but I mean from year
to year, we're starting to find that it's not at
all study. And that's a big one because one of
the foundations of radiocarbon dating is this idea that that
it's like a reliable clock that just starts clicking backwards.
You know, at any point in time, whatever year you
come in on you're going to be able to compare

(32:22):
it to a modern sample and get a coherent UM
radiocarbon date that will make sense. That's just absolutely not
the case because of all of those fluctuations, Right, That's
something that this field is definitely grappling with, which uh
it will it will be able to overcome and largely
has already because they use other types of dating to

(32:43):
calibrate their radiocarbon dates. Yeah, which is really cool. We
were talking about the um relative dating of carbon fourteen dating.
What they're now trying to do, who not now they've
been doing it for a while is absolute dating, like
what you're talking about, comparing it to own quantities. And
one of those is tree rings. And I'm surprised we've

(33:05):
talked about tree rings a little bit here and there,
but I wonder if it could be a shorty on
its own at least Yeah, maybe more. We'll just start
wrapping on it and whether if it turns into a
real deal episode we'll go with, we'll just cancel our
dinner plans keep going. But tree ring dating is called

(33:26):
dendo chronology counting tree rings, and not all trees have
tree rings. Will get to that, which can be a problem,
but a lot of them do and some of them
grow every year, just like you learned, and everyone probably
thinks it's true from like kids science class. It's like
once a year a tree has a ring, so if
you cut a tree down, you can just count the
rings and know how old it is, which is I

(33:48):
mean basically right, depending on the tree is exactly. But
here's the thing is, trees absorbed that carbon fourteen just
like everything else, but those tree rings don't. Once they
have completed a tree ring cycle, that tree ring is
essentially dead inside the tree and is not accepting any
more carbon fourteen. Yeah, it's like a fossil. It's like

(34:09):
if you look at the outside of a tree, that's
the living part. Like as big as a tree is
and enormous as it is, the actual living part of
it is just this outside veneer and like the leaves
and everything. Right, yeah, everything inside is what used to
be outside but is now inside because a new ring
of growth grew around it. So um, since it's not
taking in any more carbon, it's like a snapshot of

(34:31):
the carbon fourteen that was in the atmosphere the year
that tree ring grew. Yes, and we know this, and
now we have something to compare against those Carbon fourteen
data results. Yeah, because if you chop the tree down today,
you would say thank you father tree, mother tree, um,
for sacrificing your life for for science. That's what you

(34:54):
have to say first. Um, And you start counting the
tree rings backwards. If you it to another tree that's
much older, but that lived that the lifetime of which
overlapped with the tree you just cut down, you can
eventually jump over from the tree you just cut down
to this older tree and keep counting backwards and then

(35:15):
just keep if you find enough old trees, keep leaping
from tree to tree, counting tree rings as if it
was one big old tree. That's really cool. It is,
and there are very very old trees that do exist
on Earth that you can count backwards from over very
long spans of time. But you can also use multiple trees. Yeah.

(35:36):
And like if you're sitting at home or in your car, thinking, well,
why don't they just find the oldest tree and go there,
Like you want that overlap because you want a complete
record because stuff you're dating might fall. You know in
that that they need everything to fall in that range, right,
And so this has been extremely helpful for radio carbon
dating because they have managed to compile basically a library

(36:00):
of tree ring data UM going back like fourteen thousand,
five hundred years. It's amazing. It's called the Holocene tree record,
and it's one of the I didn't even know it existed.
Now I'm just I love it. Yeah, it's pretty cool.
I want to I like wanta a bound copy of
it for the coffee table or something and lay in
a hammock in the middle of Pando and read it

(36:22):
and read it and be like, oh, look at this year, Pando,
what do you think what happened this year? And Panda
would hug you. Uh so I was trying to think
of something you would do back to Pando, but I
would go glow and Panda's leaves. But that feels good. Sure.
So there are other places in nature that have the
same kind of snapshots. Uh, if you wanted more than

(36:45):
because you need more just than the Holocene tree record. Uh,
they can use coral reef because there's clearly carbon in
the ocean um still actites and stillagmites, which are called
spelio thembs through whenever busts out out at a party,
you'll know they're talking about. Yeah, you probably should, because
everyone else is just going to be talking about I

(37:05):
can never remember which ones are exactly. Oh you mean,
just let me educate you. Goodbye. Uh. They are made
of carbon and they are deposited in layers, just like
the tree rings in the coral uh. In fact, they
have found some in China kind of recently. They go
back fifty four thousand years. Yeah. I think they really

(37:26):
recently found this so much so that hasn't been like
fully vetted, but they were super excited about it. That
the idea that it gave a basically a long mineral
rich tree ring library of fifty four thousand years of
the carbon fourteen concentrations in the atmosphere. If they if
it does pan out, that would be amazing. And what's

(37:48):
the deal with the lake in Japan? It reliably puts
down a new layer of sediment every six months. That's
pretty cool. Yeah. And so they've taken core samples and
in these core samples they've turned up like leaves trapped
in single layers and something like six hundred and fifty
different spots. So all they have to do is count backwards,

(38:11):
find you know, the and they'll know the year that
this UM leaf is trapped in and then test the
carbon fourteen and the leaf and you've got like a
picture right there. And that is called what we'll call
a library of atmospheric carbon fourteen concentrations. Yeah, they should

(38:31):
have a name. It does. It's called ink COW I
N T C A and UM. There's different programs that
you can run all this through like before, back in
the forties and fifties, like they were, I guess, using
slide rules and stuff like this to come up with these.
Now we have basically machine learning algorithms running these these
computations for us. But UM, they have programs that use

(38:54):
this calibration library to basically say, here's the what the
radio harbon date is saying. What does this library of
absolute dates say? And then what they do is they actually, well,
the computer I should say, overlaps what's called the wiggles.
They hold it up to the light yea, and they
find like where these kind of wiggles overlap, which are

(39:16):
UM confidence intervals I guess, uh, and where it's most
confident that you have a pretty good idea of what
the range is for the age of this sample. And
that means we know exactly how old everything is always
all right precisely to the day. That is not true
because all the things we just mentioned, the spile, thems,

(39:40):
the coral, everything has its own individual problems, right. Um.
Coral turns out isn't a great material for calibrating this
stuff because ocean concentrations of carbon are not the same
as in the atmosphere. So that kind of throws it
off right there. It So if you're comparing like something

(40:02):
that lived on land to coral in the library in
cal library, yeah, it's not gonna it's not gonna calibrate
very well. Um. Tree rings are a problem too, because
they figured out that depending on the hemisphere that the
tree grew in, it will give you a different atmospheric
concentration because the southern atmosphere has more oceans and those

(40:24):
oceans absorb more carbon dioxide. So there's actually less carbon
fourteen on the land in the southern hemisphere than there
is in the northern hemisphere. So if you checked out
a water logged oak that grew in Ireland and two
c e if you found a cody tree the Cody

(40:47):
tree in New Zealand that grew that same year, they
would have different radio carbon dates because they have different
carbon radiocarbon concentrations. So it's just there's a lot of
things confounding this stuff that's keeping it and being less precise,
that's right. And it gets even worse because there have
been long stretches of time on Earth in our history

(41:09):
where carbon fourteen production really increased every year over you know,
hundreds of thousands of years or tens of thousands. Yeah,
well there's stretches that. So all over the radio carbon calendar,
there are these things called plateaus, and I think the
longest that they've ever found is a few hundred years.

(41:30):
When I said tens of thousands, just like a radio
carbon date, all right, it feel so bad. They found
this thing called the Hallstock plateau, more like the Hallstat disaster. Yeah,
that's what some people call them, all right, I'm sure
that's what Willard Libby called that. Sure, But basically there
were periods during Earth's history, This one in particular goes
from seven sixty four b C where the the production

(41:56):
of carbon fourteen in the atmosphere just in priest basically
steadily steadily every year, so nothing ever got older relative
to new stuff, right, which means that if you radio
carbon date something at the in seven sixty b C
and something in four twenty BC, they're going to give

(42:17):
you the same exact radio carbon date. Does that make
sense for that was your response. Hey, there's people out
there thinking it to the Hallstad disaster. All right, Willard
Libby would be proud. He was the wild Man. So

(42:37):
this is why old this is important. It's not just
to put a date on something so we know how
old it is and we can just put it down
in a museum or a history book or whatever. Right. Um,
it really opens up all of science and all of
ancient history to interpretation and kind of rock to the
world about a lot of things that we thought were

(42:58):
true that are true. Yeah. They call it the radio
carbon revolution, and like, well, one good example is in
the UK there we talked about Stonehenge. They used to
think that Stonehenge was the result of the how do
you pronounce that missini myceney? I don't know mycen A.

(43:20):
You'd think I know mice sna. I think it's the
mycen A civilization in Greece, But the A and the
E on the end. It's got to do something more
than like why not just add a Y instead of
an e. I'm with you, and you know sometimes you
see the A and the E together conjoined, like Ronnie
and Donnie Galleon. You know. So what is that? It's

(43:45):
its own thing. So we used to think that came
from an ancient Greek civilization, but because of radio carbon dating,
they said no, no, no, no no, no, this is uh,
we had the age all wrong. And Stonehenge came before
that ever, happened before the civilization was even there. So
it really helps clear up a picture of everything from

(44:06):
Otsy the ice Man to knowing uh that the shroud
of Turin was only seven years old. Uh. It so
it can confirm things and it can quh other things.
Right and then, and the way that they used to
do it before was they would just kind of dig
in the earth and turn up artifacts. And because an
artifact was closer to the ground than another one, it

(44:30):
just meant it was more recent. That's like as precise
as they could get. Radio carbon was like, not only
are we going to do with that, but get this
pal here's a date and a pretty good estimate of
a date that this thing existed. That's how much it
changed things. They used to be like this is older
than this. Now it's this. Let's see the ice man
was running around, you know, in and in doing that,

(44:55):
it also changes everything and that they're saying, oh well,
Letsie was also ound with tattoos on him that seemed
to suggest acupuncture, which apparently they didn't think anymore. But
but that changed our idea of how old acupuncture was.
And then he had certain tools on him. We didn't
know that they were making these tools back then, but
now that we've reliably dated Utsie, we know that the

(45:17):
the this, this toolmaking complex is much older. People had
professions much sooner than we thought. It just opens up
everything when you have a date for one thing. Yeah,
the tender rols are far reaching, right, exactly a broad
and it happened actually here in the United States to
ur in North America. You know, we did a whole
episode on the Clovis Police. Sure the idea that the

(45:40):
Clovis people were the first Americans and they came over
from crossing over the I guess the bearing Land Bridge
when the ice sheet receded, and so Willard Libby did
uh a test that showed there's no way that the
ice sheet was open anywhere before twelve thousand to five

(46:01):
fifteen thousand years ago. So he actually said a baseline,
this is when the earliest people possibly could have been here. Well,
we've been finding and radiocarbon dating settlements that are older
than that. They found one in Idaho on the Snake River.
I can't remember the name of the island. Um, that's
like almost sixteen thousand years old, and it shows definitively

(46:23):
that since the ice sheet was there, they couldn't have
come around the burying language. So now we think the
first Americans came over by boat, all because of radiocarbon dating. Amazing,
But we're screwing it all up for the future because
of human activity. Um that you know, we're burning a
lot of fossil fuels and we were releasing a lot

(46:44):
of carbon into the atmosphere, and so much so that
that that consistent, previously reliable ratio of carbon twelve to
carbon fourteen has been knocked all out of whack because
of us. And in the next what uh years, Yeah,
thirty to forty years. Uh, we may not be able

(47:05):
to date things accurately using this method anymore. Yeah. Yeah,
Because when you know, when they say, well you burn
fossil fuels, you release a lot of carbon dioxide. Well,
those fuels used to be alive, so they used to
have carbon fourteen in them, but they're so old there
isn't any carbon fourteen now, it's all just carbon twelve.
And we're releasing tons of carbon twelve into the atmosphere
that wouldn't normally be there. That's right. And uh, nuclear

(47:29):
tests that we conducted UM had a big actually had
the opposite effect. Between nineteen fifty five and nineteen sixty three,
the common concentration of carbon fourteen in the atmosphere doubled,
almost doubled. Yeah, so there's all screwy now. It is
a very screw so much so that now they have
modern samples. They have a beat harvest from the seventies

(47:51):
that they used to replace a beat from France from
nineteen fifty that they used to be like, this is
the baseline now for modern This is what we're reduced
to is sampling beats for God's say. That's how much
it screwed things up. But they have figured out how
to um use this kind of modern screw nous to
also date UM recent remains, which everyone thought was just

(48:14):
impossible Um, that you couldn't you couldn't tell when a
body lived or died if it were just a you know,
a decade or so dead or less. But we have
historical records for all this stuff. I know it's a
big deal, but like, and we're screwing stuff up to
the future. But isn't the the utility of carbon fourteen
dating because it was pre history? Yeah, that that certainly helps.

(48:38):
And yeah, I guess you're right that having a record
would definitely help quite a bit. And I'm not you know,
saying like who cares then? But at least we have
that going for us. That's a good point. It'd be like, well,
the leather seat from this automobile is the same age
as this leather shoe from three thousand years before, which
is which? Um, But yeah, they have figured out how

(48:58):
to how to use it for forensics based on your
teeth enamel, which are like tree rings, and then based
on your soft tissues. But your soft tissues degrade, so
they figured out that they can actually test the casings
from the larva that eat your soft tissues as you're decomposing.
So the soft tissue is the carbon fourteen in the scenario. Yeah,

(49:19):
which you're constantly remaking, and then as you die, it
gets it stops being um taken in, and then starts decaying.
And as you're being eaten by these you know, bug larva,
they shed their casings, and the casings don't degrade. So
you can come along and test the casings and they
ate your carbon fourteen and you can figure out when

(49:41):
that person that body last lived based on the casings
of the bugs that ate it. And in a million years,
if I were not to get cremated and they were
to bury me into the ground, the only thing that
would remain of me are the three titanium screws holding
in my three fake teeth. That's Nate. A million years,
who'd have thought, Yeah, there he is. Yeah, there's Chuck one.

(50:06):
You got anything else? There may be more than that
by then too, it might be four or five. Any so,
anything else you want to keep going that we can
keep talking about this. I have no dinner plans, Okay, Um, well,
I think we're gonna stop with Carbon four team. We
don't want to press our luck. It did go pretty well, Chuck,
I told you I think so. And since I said
it went pretty well, it's time for listener mail all right,

(50:28):
and I was preparing for the next episode. Yeah, we
got a listener mail for look at me? All right.
I'm gonna call this uh soup follow up. If you remember,
we talked about cam soup in a previous episode on
what Else Augmented Reality? Right, And I think we were
pegged as a progressive guys because you you spoke up first.

(50:53):
It's yeah with a name brand. I'm a Campbell's man. Hey,
I don't discriminate. I like Campbell's Chunky two. I just
kind of went along with it. I didn't want to
ruffle any feathers. I didn't speak up, but this is
about that. Hey, guys, there are no words to describe
how much I enjoy your podcast. I've listened to every
single episode and continue to do so each and every week.
Thank you for bringing wonderful science, exploration, for knowledge and

(51:16):
laughs to my days. So far, so good. I listened
to the latest episode on Augmented Reality while on a
plane to Boston, and I could not stop laughing. When
you got to a full on sant tangent about can Soup.
I thought, this is my moment, this is my chance
to write in I've been two Stars struck before. But
here we go. I know can Soup all too well.
I spent seven years right out of college working for

(51:38):
General Mills. Yes, they make the serial, but they also
owned Progresso. I worked in sales, managing our businesses with
our East Coast and national accounts. Three years ago, I
left General Mills and went to work for Campbell Soup.
It's like, I guess, so just outside of Philadelphia. I
guess you could say I too have a thing for

(51:59):
Cance Soup. I currently manage our soup and pray go business,
one of our largest East Coast grocery chains, and although
it doesn't seem complicated, I can tell you a lot
of work goes into you enjoying your can of red
and white chicken noodle soup. I still love that Campbel's
chicken noodle. Oh yeah, it's so good. It's like, how
do you mess with a classic like that? Well, but

(52:21):
there's also progressive creamy chicken noodles is the bomb. When
you mentioned this episode brought to you by Progresso as
a joke, I was just waiting for you to plug
that you liked Campbell's as well and even more ha ha.
Either way, I'm just glad you both enjoy eating our soups.
I would be happy to give you a tour of
Campbell's soup HQ if you're ever in Philly. Thanks to

(52:41):
the entire team for all you do. You guys are
a legend combined into a singular. That's from Kathleen and Kathleen.
Uh no shade to progressive, But I'm a Campbell's man.
I eat three soups a day. I eat Campbell's chicken noodle.
I ate chicken corn chowder. I don't know. I fare

(53:02):
that's and I eat their new England clam chowder. Yeah,
that's good. Who who eats Manhattan clam chowder? I don't know,
or I'm sorry, man, I had a clam chowder. No one,
not even Manahaddan had nights. They're like, get this away,
give me the real stuff, give me that creamy goodness.
Do you ever have meatball alphabet? No? I don't know

(53:23):
what we're in those meatballs, but I grew up on them,
and look at me now. I know. That's all the
soups I eat. Though it's weird. I have three soups. Yeah,
and you gotta do the chunky stuff Campbell's chunky, I
mean become in large cans, is like a hungry man. Well,
that's the chicken corn chowder and the I have had
that and it's good. Those are chunky. Have you heard
the chicken pot pie? No? But I just made a

(53:45):
homemade gluten free chicken pot pie biscuit topped. Well, how
do you make a biscuit without gluten? You make it
with one to one flower instead of wheat flower? What
kind of flower is not wheat flour? What is like
the white flower? Do you never luten free pasta? And
I mean I've heard of it, I haven't eaten it.

(54:07):
It's just made with flower without gluten. It's called one
to one is in the ratio. So basically you buy
the gluten free flower. Sometimes just rice flour, okay, tapioca,
But have you had chicken flower? I don't think so
it's not bad. I mean, I'm not gluten free. I
did this so Emily get enjoyed chicken pope pie. But
you know, you lay out you make the little chickenscu

(54:27):
good little biscuits and you lay them on top of
your pot pie, and then you brush it with egg yolk. Nice,
and then that Bronze is up to a shiny brown
top like people laying on the beach and so good.
That is nice. Man, make a good chicken pop. Have
you had it already but had like I haded this
past weekend, but I have not had the soup, which

(54:48):
is what led me to that danger. It's good, I
won't I don't discriminate progressive Campbell's it's all good. Well,
Chuck is checking his phone to see what time, and
it's so I guess we should probably end this episode.
If you want to get in touch a this to
offer us a tour of where you work. That's always nice.
Thank you. Um. You can go on to stuff you
Should Know dot com, check out our social links, or
you can send us an email to stuff Podcasts at

(55:10):
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