Evidence from changing 13C/12C isotopic ratio for human generated increases in carbon dioxide 

Obrigado por assistir!

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😊 Thanks!

Thanks Yixuan!!

While I did not check out if the math works, I assume your error is in the fact that the 0.4% is the change in C13 in atmospheric CO2; it is not the change of C13 in the atmosphere, which is what it sounds like you are thinking.

Using processes occurring in geologic time frames to discredit a 200 year process (the video's time frame), or a 65 year process (your Keeling Curve data) is a false argument. It in fact supports what was said in the video: Geologic time frame processes cannot possibly account for the 200 year diminishing percent of 13C, especially given its exact reflection of the data in the upper graph as well as Keeling Curve data.

Thanks for many thoughtful questions. I have looked into some of this several years ago when I came across the papers listed in the description, and this is what I found (not much): 1) It is not known why plants differentiate between 13C and 12C. One article ventured to say it was because of the difference in mass, which does not really explain anything, in particular your question about 14C, which is heavier and thus one would assume even less likely to be absorbed by plants, which makes no sense given the fact that carbon dating is reliable in plants and animals. Most stable isotopes have little to no changes in their physical & chemical properties. One interesting exception is water, in which H2O with the isotope 2H has higher bond energy with the H-O bond than water with the 1H isotope, an unusual consequence for an isotope, but I was thinking if that is the case for 13CO2, that is, higher C-O bond energy, then that could explain it-- the Calvin cycle would be unable to break the C-O bond and so the 13CO2 would just diffuse out of the leaf unused. The rate of absorption of 13CO2 into plants is less than 1% of total atmospheric 13CO2 (I did not mention this in the video to keep things simple). Let's say mass really is the issue. If so one might assume 14CO2 would be absorbed at an even lower rate, making carbon dating in animals and plants not possible. Since we know carbon dating in animals and plants is very reliable, there must be some other rejection mechanism specific to 13CO2 but I could not find anything. One thing very interesting that I did find is the differences in 13CO2 absorption in C3 versus C4 plants. C4 plants absorb a more significant proportion of 13CO2 (about 10-20% of total atmospheric 13CO2 if memory serves), however C4 plants did not evolve until ~200 million years ago, about 100 million years short of the 300 million years needed for the production of fossil fuels. So it is the C3 plants that were present 300 million+ years ago from which we get our fossil fuels. This study also further supports the finding that C3 plants take in negligible amounts of 13CO2. So I feel the evidence from people who study these things supports well enough that it is the lack of 13C in (C3) plants that ultimately produces the lack of 13C in fossil fuels. Regarding 13C decaying to 12C: 13C is a stable isotope, so it would not decay. But let’s say it is unstable, what would happen? There are three types of particles emitted from radioactive (unstable) nuclei: alpha, beta, and gamma. A 13C alpha emitter would lose two protons and two neutrons, and so the 13C atom would become a 9Be atom, so that does not work. A 13C beta emitter would emit an electron from a neutron, which turns one of that neutron’s down quarks into an up quark, which turns the neutron into a proton, and the result would be a 13N atom, so that would not work either. (A real example of that is 2H, which, when it loses an electron, becomes 2He.) I’m a little rusty on gamma emission, but I believe it occurs with heavier nuclei after an alpha or beta emission, and does not change the nuclear components. It occurs due to the nucleus being in an excited energy state and so it is able to go to ground state by emitting excess energy as gamma rays. So the bottom line is I do not have a concrete answer for your 13C versus 14C question, but it is a great question! Thanks for asking. By the way, 14C decays regardless of its circumstances (live tissue, dead tissue, a rock…). It is because its decay is so slow we do not have to worry about it as living beings. It is also because its decay is so slow that we can use it for carbon dating. BTW #2: 14C is a beta emitter, and so becomes 14N after beta emission. Hope that helps!

The C13 has not gone anywhere it just now makes up a smaller percentage of the total carbon in the atmosphere as we have emitted C12 carbon dioxide into the atmosphere. Carbon 13 is constant in the atmosphere as it is stable and cannot decay into C12. C13 will therefore be at equilibrium so, the amount of it will not change significantly over time. Finally, the graph doesn’t show a longer period of time because the trend would be the same but would simply become harder to read. Whilst there would be variations if you went further back (ice ages etc) these would not be relevant to anthropogenic carbon emissions and therefore would only serve to complicate the picture.

@@alexlewis2522 The bottom chart doesn't suggest constant at all as the percentage goes to almost zero suggesting it has dramatically decreased which opens questions.

@@mattlm64 it is the relative amount, so obviously it goes to zero, when the other rises and it stays the same. If you've got 11 football players in your team, and the other team has 11, then it's 50%. If the other now adds 10.000 players to it's team, then your teams percentage of total players goes to zero

@@ForChiddlers The co2 only went up around a quarter.

In plants there is a carbon ratio that is heavier in the lighter 12C and lighter in the heavier 13C and 14C. But coal, a fossil plant, has the same ratio found in plants but without the 14C isotope because it is radioactive and depletes overtime. So there is a lower level of 13C compared to 12C because that reflects the ratio found in plants, in this case fossil plants that made coal.

Hopefully soon. Too much to do at work!

@@CrashChemistryAcademy alright

Thanks for your comment. My wife had the same thought. I’ll see if youtube allows that kind of editing.

Its the relative amount compared to c12. As explained in the video

In plants there is a carbon ratio that is heavier in the lighter 12C and lighter in the heavier 13C and 14C. But coal, a fossil plant, has the same ratio found in plants but without the 14C isotope because it is radioactive and depletes overtime. So there is a lower level of 13C compared to 12C because that reflects the ratio found in plants, in this case fossil plants that made coal.

The most widely cultivated plants are C4 plants, not C3. Corn, Sorghum, other grasses are all C4 plants. C4 plants do indeed use 13CO2, but not indiscriminately, they still favor 12CO2. Further, one can reasonably expect (as you are) fossil fuels derived from C4 plants to add to atmospheric C13. However C4 plants evolved about 30 million years ago, and the agricultural C4 plants much later. The point is that it takes about 300 million years for plant biomass to become fossil fuel, which means our fossil fuels are derived from decomposing C3 plants, which have little to no 13C in them. C4 plants have not been around nearly long enough to decompose and change into fossil fuel.

The naturally occurring cooling and warming of the earth over geologic time is tied to naturally occurring changing CO2 levels over those time periods, with other factors at work as well. However there is no time period in the geologic record in which 1) CO2 has been this high (420 ppm currently), and more significantly, had such a steep rise in such a short (non-geologic, 200 yr) time period. Natural changes in CO2 in geologic time are far less variable and are far more gradual and last for much longer (geologic time) periods.

@@CrashChemistryAcademy Thank you sir, this all makes sense. I guess, naturally occurring changes in CO2 levels would include volcanic eruptions above and below sea level.

Not sure if there is a question there, but to clarify-- C3 plants have 13C but in minute quantities compared to atmospheric 13C. C4 plants have a 13C presence that is roughly equal to that of atmospheric 13C. The crux is that all fossil fuels--coal, natural gas, and oil--take about 300 million years to be produced from decaying plants. Only C3 plants were around 300 million years ago. C4 plants did not evolve until about 30 million years ago, and so only C3 plants produce fossil fuel, and so the 13C presence in fossil fuel is the same as it is in C3 plants, which is negligible.