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Carbon 14 dating 1 | Life on earth and in the universe | Cosmology & Astronomy | Khan Academy

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Carbon 14 Dating 1. Created by Sal Khan. Watch the next lesson: https://www.khanacademy.org/science/cosmology-and-astronomy/life-earth-universe/measuring-age-tutorial/v/carbon-14-dating-2?utm_source=YT&utm_medium=Desc&utm_campaign=cosmologystronomy Missed the previous lesson? https://www.khanacademy.org/science/cosmology-and-astronomy/life-earth-universe/measuring-age-tutorial/v/chronometric-revolution?utm_source=YT&utm_medium=Desc&utm_campaign=cosmologystronomy Cosmology & Astronomy on Khan Academy: The Earth is huge, but it is tiny compared to the Sun (which is super huge). But the Sun is tiny compared to the solar system which is tiny compared to the distance to the next star. Oh, did we mention that there are over 100 billion stars in our galaxy (which is about 100,000 light years in diameter) which is one of hundreds of billions of galaxies in just the observable universe (which might be infinite for all we know). Don't feel small. We find it liberating. Your everyday human stresses are nothing compared to this enormity that we are a part of. Enjoy the fact that we get to be part of this vastness! About Khan Academy: Khan Academy offers practice exercises, instructional videos, and a personalized learning dashboard that empower learners to study at their own pace in and outside of the classroom. We tackle math, science, computer programming, history, art history, economics, and more. Our math missions guide learners from kindergarten to calculus using state-of-the-art, adaptive technology that identifies strengths and learning gaps. We've also partnered with institutions like NASA, The Museum of Modern Art, The California Academy of Sciences, and MIT to offer specialized content. For free. For everyone. Forever. #YouCanLearnAnything Subscribe to Khan Academy’s Cosmology & Astronomy channel: https://www.youtube.com/channel/UChNPnEkW8LYZ5Rwi8_A2-DA?sub_confirmation=1 Subscribe to Khan Academy: https://www.youtube.com/subscription_center?add_user=khanacademy
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Text Comments (102)
Justin Case (5 months ago)
Well done!
Amanda Nekuda (5 months ago)
teris keris (3 months ago)
umesh maurya (1 year ago)
If an organism have ten C14 atoms at the time of death, will all atoms go for decay or only five of them will go for radioactive decay ( as explained after half life the no of C14 would be five) Is second assumption is correct then 1. Why only 5 will go for radioactive decay? 2. Which of the 5 atoms will go for radioactive decay, and why?
JP JR (1 year ago)
7:20 In 2011 physicists at Stanford and Purdue placed the whole theory of "constant radioactive decay rates" under question. They have found in some cases there is fluctuation in the rate of decay. They theorize that the fluctuation is caused by solar neutrinos which until this finding was believed not to interact with anything it came in contact with.
Chia Lee (2 years ago)
can you please put these on the khan academy app.... or prehaps I missed it. the app in regards to biology sort if ends after ecology
Rabeb Mabrouki (2 years ago)
All hot girls are here => https://twitter.com/b820da66252a48305/status/801992405775826944 Carbon 14 dating 1 Life on earth аand in the universee Cоsmology Astrоnoоmу Кhan Acadеmy
CMAenergy (2 years ago)
Science has not been around for 5730 years to prove a 1/2 life decay. That is only a theory, and not proof, Palladium rings they also used to prove decay etc, and were found to be bogus also, since they were supposed prove said and now it to is false, Your math is correct but the rest is only a theory without actual proof.
vedant (1 year ago)
CMAenergy why don’t you return to your cave? Since everything is bogus
First-Aid-Sac (1 year ago)
CMAenergy do I understand your argument?: "palladium rings are false, therefore scienctists are assholes."
CMAenergy (2 years ago)
Do a serious study of doctors who prove the decay of palladium rings are false. The truth is there, Am I on acid, Only people who will not accept a truth and only believe what someone said was true as a theory and those who do not accept anothers opinion are possibly on acid, Look into all things prove all things, Science is all about theories yet unproven, And that goes for decay of palladium rings as a 1/2 time, There was a study shown and proven that heat causes palladium rings to dissipate quickly under heat, but they found these ring were created and still there under molten rock within the earth, Do a study yourself, But just don't believe everything you hear.
M4hB (2 years ago)
are you high on acid
Wraithbackup (2 years ago)
+CMAenergy I don't think i know everything that im sure about
brimstarx (2 years ago)
@TechiesPlace : it's not just losing a neutron , this particular neutron turn into a proton, thus not affecting the mass of the atom as per defenition ( mass = amount of protons + neutrons in the nucleus ), however changing the nature of the atom dues to the amount of protons now present ( which is determined but the amounts of protons only ) Hope that's clear enough to answer your questions !
Sarge' chargE (3 years ago)
the video mentions that C-14 gets converted to N-14 by losing a neutron. If the atom loses a neutron how can it still be N-14 and not N-13
JMarie D. (2 years ago)
It's because it's not really 'losing' but that the neutron becomes a proton and an electron by Beta emission. So, despite losing a neutron, it does get a proton and the count is still then 14. (C-14: 6 protons and 8 neutrons = 14) (N-14: 7 protons and 7 neutrons = 14)
NuclearHobo42 (3 years ago)
what I wanna know is how do scientists determine the initial amount of Carbon 14, I understand the constant rate of decay but how would you determine the initial concentration of the carbon 14 within the organism at the exact time of death? The initial concentration can be effected by so many factors especially the mixture of gases within the atmosphere at the time of death which you wouldnt know unless you were there to measure the atmospheric content and the carbon 14 concentration at the time in question all you can really do is assume and make a scientific guess no? or is there some way they estimate it? Just a question I have. If someone could please answer me I would be glad kuz my evolution professor wasnt able to.
Adam MacDonald (8 months ago)
Can one test for the amount of Nitrogen 14 in order to determine the original amount of Carbon 14?
umesh maurya (1 year ago)
Go for second part of this lecture. The answer of your question is explained there
Weiss Fox (1 year ago)
You would ideally know what the material is and therefore know what it's composition is beforehand, which is usually the case. Even if they don't know it exactly, there is generally a pretty consistent ratio of carbon 14 to carbon 12 is all living things (don't know it off the top of my head, but it's mostly carbon 12, very little 14); since carbon 14 is unstable and so decays and carbon 12 is stable and doesn't, the ratio of carbon 14 to carbon 12 is how the dating usually works. Like the original comment said, it can be affected by how much carbon is i the atmosphere at that time, so there's a whole sub-field that finds that data using tree rings (it's really complicated and you would have to google it and research to fully understand. TL;DR: when a tree puts on a new ring every year, the older rings stop having their carbon 14 be replenished and it decays as if it were dead). Also, since Carbon 14 decays into Nitrogen 14, If it's airtight, e.g. some paper in a sealed jar or plant material in a cavern that is completely closed off somehow, you can use the ratio of carbon 14 to Nitrogen 14. The above answers that this dating is based on 'assumptions' are just plain false. It's impressive how far some will go to justify religion claims and conspiracy theories.
name me not (1 year ago)
this is also my question, ease someone answer this.
Tito Bruckner (1 year ago)
As explained in the video, we're not talking about how much carbon by mass "was in the organism", but rather the PROPORTION of C14 to C12 "was in the organism". And as to the question of: how can we be sure that the atomic rates of decay don't change over time, rates which are determined by fundamental atomic properties? Why not ask how we can be sure that the sizes of protons and electrons don't change over time, or why the speed of light doesn't change over time, or how we don't know that Wotan isn't messing with all our observations?
metalmanmac1 (3 years ago)
"or...if you are a plant" Good ol Sal, being so inclusive of the plant community in the audience
JackPoet (3 years ago)
most important question... How is half-life estimated?
Stephen Patterson (11 months ago)
By amount of carbon 14 taken in, by item - when it was alive. Test works poorly on "contaminated" samples or items fraudulently manipulated.
vedant (1 year ago)
By experiments
Jonathan Alvarado (3 years ago)
+jackp6 T(1/2) = Ln (2)/K
indhu agarwal (5 years ago)
My fat brother managed to make the best pole dancer there is in my town fall for him as he ran the Cupid Love System (Google it). I wish I was happy for him but I want such a sexy lady to fall for me. I am totally green with envy. Does that mean I’m a horrible person?
dhruba kandel (5 years ago)
Life sucks. My cousin has started seeing a stunning lady as 60 days back he joined a site called Master Attraction (Google it if you wish to learn more.) I'm so green with envy because I want to fall madly in love too. How come it's so difficult? I'm gonna check out this Jake Ayres man's information to find out if it can help a person like me. Funny thing is, he previously had NO success with girls. How could you change so rapidly? His lady's a banging model.
Duncan Zhang (5 years ago)
How did scientists determine that the half life of carbon is roughly 5730 years? How does one go about proving this?
SnoopyDoo (5 years ago)
I suspect that 50,000 years on the cosmic time scale is not even a blip and therefore the amount of radiation won't vary in any significant amount during that time.
SnoopyDoo (5 years ago)
The only thing I found missing in the video was that it should be mentioned that Carbon 14 dating can only be used to date stuff back to 50,000 years. It cannot be used to date stuff older than that and certainly not dinosaur bones.
libertynindependence (5 years ago)
"1/4 of the Carbon 14 that you would expect to find" I don't know why anyone can't see that as a huge assumption. If you change the amount that you "expect" to find, you change the result in a huge way!
zam dwa (5 years ago)
Why is this rate so fixed?and why is the amount of c14 in living things fixed too?
Tommie Peterson (5 years ago)
before reading my question, please understand that it is neither sarcasm nor confrontation: where in the bible is the date(s) of creation provided?
GSpotter63 (6 years ago)
Part 1) Radio carbon dating assumes that the amount of Co14 in the atmosphere has always been the same. But there again, we have no way of verifying that. The fact that insects grew to as much as 8 times their present size indicates that in the past o2 levels and atmosphere pressure (14 N) was indeed much higher. Would not those higher levels have greatly alter the formation of Co14 in the atmosphere and hence the amount or % of Co14 invalidating that dating method?
GSpotter63 (6 years ago)
Part 2) And then there is the amount of cosmic radiation. Again the carbon 14 dating method assumes that the amount of cosmic radiation has remained the same for the past 50,000 years. Just a 10% drop in radiation would result in a sample appearing thousands of years older. Can you guarantee and verify that the cosmic radiation has remained the same?
GSpotter63 (6 years ago)
Part 3) As you can see, it takes a lot of assuming (AKA faith) to hold to the old Earth theory. Interesting, if the history of the world as it is outlined in the bible is true ( massive changes to the atmosphere and the geology at the time of the flood) than the Co14 dating method dos not require any assuming for it to fit perfectly.
that (6 years ago)
Let me guess, the Bible? Get out of here.
Sky Lake (6 years ago)
But, you can only date girls that were once alive :o
amaizenblue (6 years ago)
Carbon dating is only useful up until about 50,000 years. Anything more than that, and there is not enough carbon-14 left to measure. With new measurement techniques, they are trying to increase that limit to about 80,000, but it is unlikely to go much farther than that. So no, one cannot detect carbon-14 in dinosaur bones, since they are at least 65 million years old.
amaizenblue (6 years ago)
Everything absorbs at about the same concentration as is in the atmosphere. No, that concentration does not remain constant. But we can identify the changes in concentration throughout time by comparing the carbon dating with other forms of dating techniques that do not use radioactive decay, like dendrochronology, varve chronology, coral dating, etc.
amaizenblue (6 years ago)
That's why we calibrate it against dendrochronology, speleothem dating, coral dating, ice core dating, varve chronology, and others... Scientists don't assume that the concentration has always been the same. In fact, we know that it hasn't...and we correct for it. In fact, we use that knowledge to learn new things about the atmosphere around that time...like maybe a volcano erupted
amaizenblue (6 years ago)
Yawn. Kent Hovind, really?
thoughtinprocess (6 years ago)
Watch this video, from the time that I posted. /watch?v=gb8uiOD01sU 5:24 - 7:29
Thad Haines (6 years ago)
The only thing that in my opinion makes C14 dating unreliable past a certain point is the fact that we don't know the earth has made the same amount of C14 in the past as it is now. Atmospheric changes since creation would suggest that C14 formed at a different rate as compared to now therefore making our constant we compare with inaccurate.
jimi riddle (6 years ago)
that all makes sense, but what i don't get is how we can know 1/2 of the carbon 14, in a bone, is gone.. how do you know its 1/2 or a 1/4 of the carbon 14 that it started with, you'd have to know the amount it started with to say its 1/2... does everythin absorb a set amount, is carbon 14 created at a constant rate?
Isidore David (6 years ago)
Thanks for this instructive lesson on Carbon 14 dating.
Sky Lake (6 years ago)
I wonder if it's still possible to detect carbon-14 in dinosaur bones. Like, does the rate at which carbon-14 slow down inversely exponentially?
Daniel Jensen (7 years ago)
I'm mostly dating girls...
vicksoma (7 years ago)
@AngelKnight85268 Potassium-Argon dating is used for dating things that are millions of years old. It's half life is 1.25 billion years. Sal made a video about it in this playlist.
Maracachucho (7 years ago)
@AngelKnight85268 The general term is radiometric dating, which is composed of a lot of different methods based on uranium, potassium and carbon (among others i don't remember of course).
paulceltics (7 years ago)
100th like
hahs4 (7 years ago)
that is so sad, I will not be able to eat anything containing C-14 once I am dead
Stephen Lee (7 years ago)
I dated a carbon once, she was clingy.
Andrew Sindel (7 years ago)
At 4:17 it is stated that we are mostly made up of Carbon 12 and only a small portion of us is Carbon 14, but at 8:51 the quote was "one-half the Carbon 14 of all the living things you see." My question becomes this: How can you be sure that there was a specific amount of Carbon 14 in the body to begin with? Does age come into play? What if the bone was from a person who was a herbivore or carnivore? Does that make a difference?
Sam Carter (8 years ago)
thank you for sharing your knowledge with us... appriciate it. well done! sir
Sam Carter (8 years ago)
thank you for sharing your knowledge with us... appriciate it. well done! sir
animals0feel1pain2 (8 years ago)
Can someone explain how you measure C-14? Do you compare it with the ratio of N-14? Or do you compare it with the ratio of C-12? Because it seems that measuring the amount of C-14 doesn't do you any good, since obtaining a larger sample of carbon would yield more C-14 atoms.
ScaredCrows (8 years ago)
Erling Andreassen (8 years ago)
Hihi, some religious nut complaining about C-14 dating again? Relax, oh ye believers, science has some 15-16 other accurate dating methods too..so you'll lose anyway if you try to fight science/reality.. Hehe! : )
mrhnm (8 years ago)
@Hooya2 but carbon dating cant be right it cant accurately date stone tools! Warning: That was sarcasm.
Stephen Patterson (11 months ago)
that's because stone tools aren't living to begin with. Only works "best" with organic samples.
Waranle (8 years ago)
Thank you Sal
trident3b (8 years ago)
@khanacademy: so sorry, but something entirely irrelevant, but which application do you use to produce your tutorials and do you use something like a wacom pen to do this too? Apart from that very much like your lectures.
Lavabug (8 years ago)
@CogitoErgoCogitoSum You should pose that question to a nuclear physicist. I believe it involves testing for beta decay on shorter timespans and later extrapolating. The fact that the predictions it makes are consistent with the concentrations found in progressively deeper fossil remains also helps.
jaynkay100 (8 years ago)
@CogitoErgoCogitoSum Do it yourself or GTFO. Otherwise don't expect people to believe your, so far ignorant and indistinct, accusations. Feel free to PM me with a nice citation explaining why carbon-14 relies on assumptions, and fallacies. I'd be quite happy to provide you with an education in the realities of radiometric dating methods.
CogitoErgoCogitoSum (8 years ago)
@CogitoErgoCogitoSum The problem with out society is that you have "believers" such as clerlic there, who blindly and faithfully believe whatever academia preaches them.
CogitoErgoCogitoSum (8 years ago)
@CogitoErgoCogitoSum Sal of the Khan Academy, perhaps you would like to post a video explaining all necessary assumptions and all leaps in logic that were required to formulate C14 dating in the first place? Youve done math proofs before, why not a C14 dating proof. Teach us its limitations and its fallacies, as any good scientist should know.
CogitoErgoCogitoSum (8 years ago)
@CogitoErgoCogitoSum There is truth, which is what I said. And there are assumptions necessarily made to make C14 dating work - if it even does. And there are those of you who resent the prospect that C14 dating is wrong, for whatever prejudiced and bigoted reason.
CogitoErgoCogitoSum (8 years ago)
@clerlic If youre so smart, why dont you debunk me with reason instead of attacking with rhetoric?
00Shahad00 (8 years ago)
my head hurts
noxure (8 years ago)
@Houston810 Yes but he's talking about the element N, not the substance nitrogen.
superdau (8 years ago)
@siggyboss It doesn't matter, because it's the ration of C-12 to C-14. If you eat more you eat more of both, so the ratio stays the same.
Houston Davis (8 years ago)
isn't N(g) a diatomic gas?
Bruno Antunes (8 years ago)
eggie545 (8 years ago)
the next part he alludes to is about exponential decay diff equations...
GeologyJack (8 years ago)
To back Hooya2 up, it is true that the rates are not constant but we actually have the ability to find the concentrations of C-14 in the past. We can determine direct ages via ring counting of stalagmites and stalactites. Due to the nature of these formations, they lock away atmosphere in a way that there is no mixing with the current concentrations, Through this we have a record of the concentrations of the past. It is also worth noting that the amounts correlate directly with ice cores.
AcanLord (8 years ago)
@Hooya2 You are right. i double checked. Its phosphorous, not sulphur my bad.
CogitoErgoCogitoSum (8 years ago)
@AcanLord Thanks for that trivial tidbit. You missed the point entirely. Yes, I made a generalization.. "oh my god". You have totally undermined all twenty of my points by barely touching on one.
AcanLord (8 years ago)
@inad316 You are talking about the Arsenic Bacteria found in Mono lake. It still contains carbon, the element this bacteria replaces in its biochemistry is Sulphur.
AcanLord (8 years ago)
@CogitoErgoCogitoSum -- We assume that all life as about equal C14 concentration even at this very moment - --- No we don`t really. C-14 concentrations in marine enviroments are much lower and not as uniform as in terrestrial enviroments, Consequently it is not considered useful in dating remains found in marine enviroments.
cyberprodigy (8 years ago)
Thanks for explaining. Now I finally know how they are doing C14 dating (;. But I guess few thousand years ago carbon 12 isotope was less common then today.
CogitoErgoCogitoSum (8 years ago)
Oh, and finally... when was the last time we went back in time to verify our results? C14 dating has never been empirically confirmed. Not even with statistical or probabilistic reasoning. All we do is rely on current-world observation.
CogitoErgoCogitoSum (8 years ago)
We also assume that asteroids, floods, tectonic activity, etc, have not had an adverse effect on C14 concentration in the oceans or atmosphere. We assume that all life as about equal C14 concentration even at this very moment - we fail to consider that C14 concentration is not homogeneous worldwide, and we also fail to realize some animals/plants may in fact prefer C12 over C14, or vice versa - affecting their C14 concentration and all life higher in the food chain.
CogitoErgoCogitoSum (8 years ago)
@CogitoErgoCogitoSum Carbon dating is not performed without bias. The tests are not blind. Two different samples from the same bone have yielded gross discrepancies. Results that dont conform to the archeologists expectation are usually thrown out, and rationalized as having been somehow "cross-contaminated". Most scientists today will admit that C14 dating is only accurate to at most 4000 years - not even one half-life of the isotope.
CogitoErgoCogitoSum (8 years ago)
@CogitoErgoCogitoSum That we can accurately measure concentration of atomic isotopes, in as small quantities as we do find, locked away in bone, without relying on decay analysis (using consequent to prove antecedent, effect to prove cause) C14 creation rate has remained constant. *And none of these points are absurd. Real statisticians and scientists have performed research which invalidates all of the assumptions.
CogitoErgoCogitoSum (8 years ago)
Carbon-14 Dating Assumptions: The proportion of C14 in atmosphere and organic tissue has remained constant over the centuries. C14 cannot enter a dead body. No other variables can affect decay rate. 5730 years is precise, and that error does not compound with time. Planet did not already contain c14 naturally at its creation, strictly created by sun in upper atmosphere and began at 0. C14 decay and creation rate are at equilibrium
einsteinino (8 years ago)
@vpletap Or, better, ¹⁴C.
16jrsoccer (8 years ago)
thats crazyyy, i just started this unit in school today.. aha youre the best.. also think about doing some genetics in the biology tab?
Christopher Loughrane (8 years ago)
oh and btw great vid!
Christopher Loughrane (8 years ago)
oh yea. first!! haha

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