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Thanks Shawn. There is one proviso to remember in isotopic dating methods: The starter and daughter elements can be removed at different rates, by things such as leaching, diffusion and evaporation. Those different rates can give misleading results. For instance, Noble gases, such as Helium, Argon and Radon seep out of rocks over time, sometimes quite rapidly, and Nitrogen can be removed by biological activity. Fractions and percentages: Surely every ten year old child has been taught both formats? They're the fundamental building blocks of mathematics and everyday life.
Thanks Shawn, I always love your ability to show difficult material in a clear and easy way to see it. I really loved geology from an early age, but I was terrible at math and science and decided it was too hard for me. I have used fractions all my life as a carpenter and get that easily.
I always think of myself as an 'F', hating fractions. This was because of one test at 8 years old. This is rubbish. I am perfectly capable, but old habits die hard! Thanks Shawn for confirming that a good teacher makes learning enjoyable.
I got to quiz 3 and decided age is relative. 😁 Love these videos - thanks so much. I always learn something that helps me keep up with my grandson's infinite curiosity.
Thanks for another great video, Shawn. I have always had a sticking point with maths and numbers, it's never changed but I loved your tables, it was more visual than numerical and I am a visual person, so I'll give those tables a try. I did understand about half-lives, great to have some revision for it, as I used to be an oncology nurse and worked with medical radioactive sources at times.
I hope the gentleman spewing nonsense on your last video comment section about geologists not practicing science because they don’t test their hypothesis also watches this video. Thank you for your wonderful video series, I have throughly enjoyed it and look forward to going through your road cut videos with all of this new knowledge from the 101 series.
Thanks! I feel somewhat intelligent that I was able to pass that quiz while doing the math in my head. Mind you, I probably haven’t had to do this type of critical mathematical thinking since 1993. 😂
Suggestion for slight change to one slide (the video is out now, so the change would be for your class.) In the second problem (age of the granite), perhaps both the answer and the table could have used the same abbreviation for the age (Ma/Ga) rather than having m.y. in the table. Regardless, another clear, easy-to-understand lecture from one of the Internet's favourite Geology profs! ❤
I'm old enough to have learned and used fractions in life and my work. I prefer decimals, but that's a whole 'nuther issue. Great explanation of half-life dating, Shawn. Your series and volcano coverage has made me look at rocks on the ground much differently. Living in southern Ohio near the Ohio River, we get the opportunity to see a lot of sedimentary rock with lots of fossils in them of shells, trilobites, leaves etc. The road cuts expose a lot of them. Further south in Kentucky it is not unusual to blast that rock to clear areas for further development or mining. There are some spectacular road cuts down there if you ever visit the area.
A great series; I'm learning a lot. One question on dating though... I understand (sort of) how Carbon starts at 100% (or is it at a known ratio?) when it's captured by plants. But why does Uranium 325 start at 100% (?) at the moment the lava solidifies? Surely the radioactive decay was going on whilst still lava. Is something separating the 2 isotopes in the lava state?
The chemistry separates them - oversimplifying here, Zircon can incorporate uranium into its crystal structure chemically, but it cannot incorporate lead. Therefore, any lead present in a Zircon crystal must be from radioactive decay of an element that can be chemically incorporated into the Zircon, mainly that isotope of uranium.
And that should be stated at the start of the problem. Unless you know there's no other source of lead in fresh cystalised zircon the calculation is meaningless. @wingnut C-14 is formed in the upper atmosphere at a fairly constant rate by cosmic rays hitting nitrogen. This is balanced by decay to give a constant proportion of C-14 in atmospheric carbon (somewhat less than 1%). Living things are constantly exchanging carbon with the environment, maintaining that proportion within themselves. Dead things stop exchanging, starting the clock.
To add to onto radiocarbon dating info above: In reality, C-14 rates are known to have not been exactly constant throughout time; due to shifts in the radiation received (solar activity, stellar environment, etc.) or in the atmospheric carbon cycle (volcanic activity releasing old carbon, shifting vegetation patterns due to climate etc). This fundamentally limits the accuracy possible without cross-checking (vs ice cores, sediment layers, etc) - so older samples often have wider possible ranges as we have characterized those time ranges more poorly, and younger samples can sometimes have *multiple* possible date ranges from radiocarbon dating due to shifting C-14 ratios!
@@bluerendar2194 To add to this conversation the variations in the rate of carbon 14 production while problematic in absolute terms spikes in carbon 14 can be used to calibrate and correct for these variations as the incorporated carbon generally is representative of the atmospheric prevalence of the carbon isotope relative to its stable counterparts carbon 12 and carbon 13. Unfortunately there is another complication to this related to the burning of fossil fuels which are due to being millions of years old basically absent in carbon 14 and thus dilute the carbon 14 in the atmosphere causing things to appear disproportionately older as carbon dioxide concentrations rise if not accounted for. Luckily there is another isotopic bias between carbon 12 and carbon 13 where chemical reactions of life and also the incorporation of carbon into crystal structures of rocks both have a strong bias towards the smaller carbon 12 over its heavier carbon 13 counterpart which thus means volcanoes have a carbon 13 bias. This allows us to disentangle the amount of carbon added to the atmosphere from fossil fuels relative to volcanoes meaning we can calibrate for this contamination too.
I know it's possible, but I would love to know how many actual "years" have passed since a rock was dated to. I know this is something waay beyond the scope of a 101 course, but wow that would be something! Thank you for stirring the imagination!
Zircons are fascinating since they are so durable that they can survive rock recycling surprisingly including igneous recycling as Paleozoic to Precambrian zircons have been recovered from hot spot volcanoes. Experiments and modeling have subsequently verified that Zircons can indeed survive subduction recycling within the asthenosphere as well as remelting and eruption again back onto the surface. It is a mind bogglingly durable mineral. Fractions are generally more accurate than percentages since you don't have to worry about significant figures so yeah though it does mean you have to handle division problems. And frankly a percentage is really a standardized fraction of 100.
My major question is how they determine half lives that are billions of years. In reading about Carbon 14 I saw that they cannot use it on any thing since 1950 since the ratio of CO2 has increased.
Potassium-Argo dating has a half life of 1.25 billion years . Rocks older than that they could use Uranium-Lead dating as it's half life is 4.5 billion years old.
As mentioned, for some metamorphic rocks, they can be dated from recrystallization. Alternatively, some other methods include relative dating compared to rocks that can be absolutely dated (e.g. last video, if we know a rock is younger than one igneous formation but older than another) or connecting to the ages of other rock formations that can be absolutely dated (e.g. fossil dating, looking for the extension of geological features, i.e. where else the rock shows up above ground)
How does science verify the decay rates and deep time are accurate by other dating methods? What happens if evidence supports other conclusions outside the decay rate models?
Take a known amount of the element, calculate how many atoms it contains, count the number of decays in a certain time, and divide that into the total atoms. And Bobs your uncle.
Great info and Fun quiz. Just to float an idea that for non Americans (the rest - - some small fraction 😊) that Popcorn is a largely unfamiliar substance. Certainly in Europe we are long used to the idea of 'half-life' after decades of contemplating daily readouts of Strontium90 in our daily milk, (This used to be a small print banner headline on newspapers in the 60s) Iodine and Caesium varieties from fun Chernobyl and a pile of stuff leaked out of our own friendly neighbourhood plants like Calder Hall (Sellafield/Windscale) Dounreay and Cap leHogue All busy making bombs for peaceful defence purposes. Popcorn would only have a real half life in Cumbria County England. Great video apart from the culturally inappropriate classroom example 😅.
Measuring the decay rate. E.g., the radioactivity of a sample of the isotope is measured, and corresponds to 0.0100% decay over 1 year, giving an approximate half-life of 692.8 years. For most radioactive isotopes, it's usually done comparatively (so you don't need to know the starting proportion) - e.g. measure the radioactivity at one time, then measure it again a year later and see how much it decreased. It's even possible to isolate out specific isotopes out of a mix of radioactive isotopes by investigating the decay modes and energies. For very weakly radioactive elements, we take huge samples of known proportion and count individual decay events.
Canada has the oldest known rock on the planet. The Acasta gneiss. 4000Ma Very well written page explaining it: (add the slashes and dots as needed). natural-resources canada ca simply-science where-do-you-find-old-iconic-rock-stars-canada-course 24979 and this page: science gc ca site science en educational-resources history-geological-survey-canada-175-objects 126-acasta-gneiss-1983
Since we know the elemental decay rates, what of solar mass ejections? The sun would be much larger billions of years ago, putting the earths orbit out of the “Goldilocks zone”. So much for evolutionary theory. Carbon dating? About as accurate and effective as online dating💯✌️🦚
Perhaps you could write up a paper detailing your research into this. Then present that to the International academy of the earth sciences for review. Who knows, you could be rewarded with a Nobel prize instigating the rewriting of the textbooks of Geology ect.
