Is There Circular Reasoning In Radioactive Dating?

[Guest BackSlyder]

In my preparing myself for random discussions/debates with creationists, I know that claiming circularity is one of their favorite claims to make. In searching for answers to this, it cannot seem to find a straight reply. It seems that all of these scientific assholes do not know how to speak english, and I am a pretty sharp person. Even the "responses for the layman" are garbled and full of bullshiting.

 

Could someone please explain to me how radioactive dating works? Or direct me to a real website with real, non-bulshit answers to these questions?

[Ouroboros]

I'm not super-good at this, and I will pull this knowledge from my memory, which isn't the greatest resource I have.

 

In the atmosphere there is a constant ratio between C12, 13 and 14. Most of it is C12, very little C13, and extremely litle C14. C14 is radioactive and will break down to Nitrogen, and has the halflife of around 5000 years. But because of constant background radiation the C14 is kept up, and this background radiation is pretty constant, and I think other studies show that it has been fairly stable for quite a long time.

 

Now when you live, or animals and plants live, you will keep on taking in the mix of C14 and N and C12 etc. But when you die, you stop replenish this stock of isotopes. And background radiation doesn't affect the N either, so the beta-decay of C14 will be fairly undistrubed.

 

(oops, I have to hurry up. family calling. I'll make it short)

Now, over time, less and less C14 will exist in your body (after death), and the ratio will change. And because the ratio is constant, by measuring the amounts of N, C12, C13 and C14 you can pretty well establish the original amounts of C14, and hence also estimate how long ago.

 

But because only a very small amount of C14 is in the mix from start, the method can only be used up to some 50-60,000 years, and also the mix can be affected if the lifeform lived in a condition where the ratio was skewed. I think the 50,000 year old *living* snail story or whatever is an example of that. The snail lived in an environment where very little C14 existed from start, so it didn't get the common mix, even while alive. So it's important to establish the living conditions too.

 

Have to go... later.

[Sceadugenga]

Circular reasoning? Not sure what you mean by this... but I'll try and explain some dating methods in layman's terms for yah.

 

Radioactive isotope dating - (basically Carbon dating, Potassium-Argon Dating, etc)

Organic matter absorbs and builds up radioactive isotopes from the enviroment as the "matter" lives - this process of absorbing these isotopes stops when the matter becomes "dead" because the isotopes no longer bond to the living cells. All this is important to understand why it can only be used to date organic matter, and to understand the process at a basic level if you want to argue with the Creationists... okay as for the science of how you can date things with these radioactive isotopes.

 

All radioactive isotopes decay at a set and firm rate - a rate called a "half-life", which means how long it takes 'x' amount of say carbon to become 1/2'x'; and more importantly as the isotopes decay they turn into something else (so as one decreases, the other increases)... so if Carbon 14 halves it's concentration every 5730 years or so, you can work out the age of something by looking at how much Carbon 14 is left.

 

Other dating methods

Now since the Fundies love trying to argue that dates reached with Radioactive Dating can be wrong it's important to realize that there are other dating methods out there - which rely on different principles (geology, astrophysics, chemistry, botany, stratigraphy, etc.) and which are ALWAYS used to confirm dates... in modern archaeology you need usually three seperate dating sources to 'confirm' a date; basically you need to confirm your sources to make sure there isn't a mistake or anomoly skewing the results.

[Ouroboros]

Sce gave a more scientific explanation than me.

 

Anyway, I remeber that I knew the facts and explanation when I was a Christian, but the problem I had wasn't the method in itself, but how scientist could guess how much C14 a living organism supposedly had when it died. It's okay to calculate the halflife backwards etc, but if you don't know how much it was to begin with, then the formula does no good. It wasn't until I got the explanation of the constant ratio of C14/N in the atmosphere that it started to make sense.

 

And Sce is correct, there are other dating methods used simulateous. C14 is only one method, and usually they use several, and sometimes depending on what they measure, some methods are not usable, and sometimes one or two methods will be off because of interfering factors.

[Guest BackSlyder]

Ok. That makes things a bit clearer. But I also have another question. How do scientists know how long a "half-life" is? How do they know that the half-life of C14 is 5000 years. Obviously, they weren't around to watch the clock. What methods or instrumentation do they use to determine these things?

 

I'm curious because I am only a recent de-convert from fundamentalism. So these creation arguments are still floating around in my head without answers to them. My de-conversion was due to philisophical reasons rather than scientific ones.

[HuaiDan]

How do they know that the half-life of C14 is 5000 years.

 

Incomplete answer here, but one method is to use a sample of a known age, dated using other methods. For example, using a sample from a document known to be penned during the reign of Julius Caeser. You don't need to wait the full 5000 years to determine the half life. Any length of time will do, with greater accuracy coming from an older sample. Simple arithmatic to figure where the sample falls on the curve.

[Sceadugenga]

Ok. That makes things a bit clearer. But I also have another question. How do scientists know how long a "half-life" is? How do they know that the half-life of C14 is 5000 years. Obviously, they weren't around to watch the clock. What methods or instrumentation do they use to determine these things?

 

Sort answer - Nuclear physics.

 

Long answer - all radioactive isotopes discovered (or created) decay at an expodential rate, a rate that varies from one radioatice isotope to the next - so some of the fancy new ones created in labs may only last milliseconds, whereas others in nature can last 100000 of years (basically the earlier they are in the periodic table the more stable they are, and the long it takes them to decay... mostly). Now if we know that nuclei decay at a expodential rate thanks to numerous experiments and observations one can then determine something's half-life by taking a sample of these radioactive isotopes, isolating it, and then constantly measuring it to see how long it takes it to go from 100% to 99% or some other measurable decrease - then you plug that time into a basic formula, and presto you've determined the half-life.

[Ouroboros]

I used to have a document explaining how it all worked and how it was established, but it was on one of my older computers and lost it when I reinstalled Windows on it. And it had the formula Scead talks about too. To bad, it's lost in the void...

[Grandpa Harley]

Anyone checked wiki?

[qadeshet]

Isochron Dating

[RedFox]

From somewhere, I remember a possible creationist claim about the dating of rock layers being circular with both fossils and radiometric dating being used to date them. They're not understanding the difference between relative and absolute dating. Relative dating is done with the superposition principle that says older rocks are on the bottom and the younger ones are on the top unless they've been overturned in a mountain building event. The relative ages of fossils and rock layers can be determined in this way. When radiometric dating was invented, it became possible to find absolute ages, with actual figures instead of just an order applied to the rocks and fossils in them when it is possible to date the fossil bearing rocks. Volcano ash layers between other layers can also be dated, putting bounds on the ages of rocks and fossils in between them. Here's the Talk Origins page on this claim. http://www.talkorigins.org/indexcc/CC/CC310.html

[Antlerman]

The thing I find most amazing about the Creationists arguments against methods used in science is the fact that they, as non-scientists have found these gapping holes in the types of tools used by science, that all the world's scientists themselves have somehow simply overlooked! Simply amazing.

 

Are we to envision that all the scientists, in all the varying fields, are just bumbling about every day, all making the same mistakes without anyone ever questioning anything, until a bunch of non-scientists who read an ancient book about a tribal volcano god transfigured into a all powerful deity, start with the a conclusion based on their particular reading of said ancient text that their flavor of deity caused all of it to happen, who then in turn set out to disprove other theories by poking holes at it, rather than offering any useful science themselves (which of course, they being non-scientists are incapable of doing).

 

My point is that even though the information above about dating methods is good knowledge, I wouldn't waste my time arguing the methods with people aren't scientists themselves. Instead I'd just point out the absurdity of their position and how foolish they look in what they're really saying in all of this.

 

Here's something I would highly recommend looking over. There are 14 short chapters with links to the next or previous at the bottom of each page. The one I'm linking to here is about "Evolution Deniers" that I think should give you a really useful perspective on all this when dealing with so called Creationists. http://www.lhup.edu/~dsimanek/philosop/denial.htm

[Ouroboros]

Antlerman touches a very good point. Just to give my little addition to it, consider that it was during a time when mostly everyone believed in a god of some kind, and a creator of the universe, that questions were raised about the age of the Earth and the Universe. It wasn't like a conspiracy of religious antagonists first rose up and then invented some ideas to argue against creationism, but the religious people themselves that started to see the contradictions and problems with the literal and fundamentalists view of their own faith. In other words, the first steps of modern atheism and science and rejection of the religious came from the religious groups themselves. If any religion did have the answers and were undeniable true, then this wouldn't have happened. So how is it explained, unless the truth is what science conclude today about life, origin and the age of the universe?

[MrSpooky]

Ok. That makes things a bit clearer. But I also have another question. How do scientists know how long a "half-life" is? How do they know that the half-life of C14 is 5000 years. Obviously, they weren't around to watch the clock. What methods or instrumentation do they use to determine these things?

 

I'm curious because I am only a recent de-convert from fundamentalism. So these creation arguments are still floating around in my head without answers to them. My de-conversion was due to philisophical reasons rather than scientific ones.

 

My favorite method of radiometric dating is Uranium-Lead Dating:

 

http://en.wikipedia.org/wiki/Radiometric_d...ting_techniques

 

1. Uranium decays to lead. The half-life for this process is 700 million years for U235, 4.5 billion years for U238.

2. As Zircon crystals form, uranium atoms can be incorporated into the crystal structure, but lead cannot. Zircon is also resistant to heat, and rather high temperatures must be met for the metal atoms to leak out.

3. Thus, any lead atoms in a zircon crystal can only have come from uranium that degraded into lead.

4. We then measure the ratio of uranium to lead to arrive at the age of the rock we're dating.

5. Extra note: Since there are 2 individual and separate molecular clocks, U235 and U238, the uranium-lead dating has a built-in cross-check so we can double-check the accuracy of our numbers.

 

*The margin of error for uranium-lead dating is therefore less than 1%

[MrSpooky]

The thing I find most amazing about the Creationists arguments against methods used in science is the fact that they, as non-scientists have found these gapping holes in the types of tools used by science, that all the world's scientists themselves have somehow simply overlooked! Simply amazing.

 

I recently conferred with an ex-Creationist who made this very point. He mentioned that when he went out into the world of debating evolution, he was shocked to discover that many people had known his arguments for the longest time and had debunked them decades ago. This is because the manner in which he was taught this stuff made it seem like he and other little Creationist kids were privy to a special, secret truth that the secular world didn't want them to know because there's a conspiracy of atheistic scientists out there.

 

Just goes to show you how insular Evangelists can be.

[Sceadugenga]

The thing I find most amazing about the Creationists arguments against methods used in science is the fact that they, as non-scientists have found these gapping holes in the types of tools used by science, that all the world's scientists themselves have somehow simply overlooked! Simply amazing.

 

Are we to envision that all the scientists, in all the varying fields, are just bumbling about every day, all making the same mistakes without anyone ever questioning anything, until a bunch of non-scientists who read an ancient book about a tribal volcano god transfigured into a all powerful deity, start with the a conclusion based on their particular reading of said ancient text that their flavor of deity caused all of it to happen, who then in turn set out to disprove other theories by poking holes at it, rather than offering any useful science themselves (which of course, they being non-scientists are incapable of doing).

 

My point is that even though the information above about dating methods is good knowledge, I wouldn't waste my time arguing the methods with people aren't scientists themselves. Instead I'd just point out the absurdity of their position and how foolish they look in what they're really saying in all of this.

 

Here's something I would highly recommend looking over. There are 14 short chapters with links to the next or previous at the bottom of each page. The one I'm linking to here is about "Evolution Deniers" that I think should give you a really useful perspective on all this when dealing with so called Creationists. http://www.lhup.edu/~dsimanek/philosop/denial.htm

 

I also suspect a strong undercurrent of "sectarianism" (at least at the beginning) motivating alot of the resistance to data or research counter the Creationism - the fact that many of the early paeloanthropologists and such happened to be 'evil' Catholics (or worse priests) was I'm sure just another bit of ammo in the anti-Catholic (heck anti-European Protestantism) rhetoric that one can still see in the American evangelical/fundie movements.