Explain...?

Question

how the radioactive decay of certain elements can be used to determine the age of Earth materials. Do you think that this is a reliable technique? Why?

Answer 1

It's scientifically sound, but there are some problems with it that make it fairly inaccurate in certain situations (carbon dating which you hear about all the time isn't too accurate for things older than about 750000 if memory serves and of course if the sample has been exposed to a lot of carbon from non atmospheric sources in recent history, it'll mess up the calculation)but for the most part it's good, it's not going to give you the exact day or anything, but you'll know if it was 50000 years ago, or 40000, or 30000, and so on

Radioactive elements have set half lives, meaning in any sized sample of the atoms, it takes a given amount of time for half of them to decay.  So if you have 100 and the half life is 10 seconds, after 10 seconds you'd 50.  After 20 seconds you'd have 25.  After 30 seconds you'd 12.5, and so on.  The example here, carbon 14, has a half life of about 5000 years

So carbon 14 decays into another stable form of carbon, so if you find something and can measure the amount of stable carbon and the amount of radiocarbon(the decaying type of carbon) left on it you can deduce how much radiocarbon the sample started with and how much has decayed.  Since you know how long it takes to decay you can figure out how old it is

Edit:  So for a simplistic example, let's say I find a bunch of dead fossilized wood (whoo exciting), and using a microscope, spectrometer, and presumably magic I find out that there are 5,000 decayed carbon atoms and 5,000 undecayed radiocarbon atoms.  That means originally there were 10,000 radiocarbon atoms, but half of them have decayed.  Since we know the half life of carbon is about 5000 years, we know it's about 5000 years old.

Answer 2

Basically, a ratio is created.

So, say for example you were using carbon dating to determine the age of something, the parent material is carbon-14, and the daughter material is carbon-12, the older something is - the more half lives it would have gone through, and the more carbon-12 there would be in comparison with carbon-14.

And well yes, it's a very reliable technique... there's no better technique, and you can determine pretty specific ages with this.

Answer 3

Radioactive decay data is based on half life. Now, it is only reliable if it was once living, because then you can use carbon 14 to date it. Carbon 14 has a relatively short half life. When you get into other elements, they have half lives millions and millions of years long, making them unreliable, since many things from that long ago do not currently exist.

Carbon 14 changes into Nitrogen 14. Each half life is 5,700 years long, making it very reliable. Now, if I have 200 grams of Carbon 14, in 5,700 years, I would have 100 grams of Carbon 14 and 100 grams of Nitrogen 14. Then, in another 5,700 years, I would have 150 grams of Nitrogen 14 and 50 grams of Carbon 14. And it goes on...

So, if I find a bone that is 50% Nitrogen 14 and 50% Carbon 14, I know that it has decayed for one half life, of 5,700 years.

Email me with any questions.