Radioactive dating...?

Question

How does...
1.) Potassium-Argon Dating work?
2.) Carbon-14 Dating work?
3.) Uranium-238 Dating work?

Please explain as best you can... Thanks!

PS--I don't think I posted this in the right category so sorry if I didn't... xP

No, I don't think your link works correctly... -_- Could you please double-check it...?

Omigosh Jessica u r such a queerdo...

thanks, tkquestion! that was really helpful!! :D (but i think ure math's off... >.<)

if you can explain it in a teensy more detail i would be sooo grateful, but if you can't, thanks anyways! ;)

Bruce D, i think you just copy and pasted it...

Please, can you say it again...

...in normal ENGLISH this time...? O_o

But if you didn't copy and paste i appreciate your time and effort... but i still would like english. xP

Okay, never mind, bruce (yes I'm sorry... I'm very random and strange)... I saw your other questions and i think you're just a very smart guy ;)

...but still may i have english...? O.O

Answer 1

All those radioactive dating works the same way.

All elements have what is called a half-life. What this is, is a period (usually in years) where the amount of certain elements in the object becomes half of what the original values were.

For example, carbon-14 has a half-life of 5730 years. All living things contain a certain amount of this carbon based element. If the object had half of what it should have, that means the object has been dead for 5730 years. If it had 1/4, then it means it was alive 10460 years, and so on.

Potassium-argon has a half life of 1.26 billion years. Uranium 238 has a half life of 4.46 billion years.

They are used to measure different range of dates.

Answer 2

As a geologist I use this all of the time. I also have to explain it to school children who come to the lab. Here is the model I use.

All radioactive dating uses the same principles. Grab a really big bag of M&M's. Dump them out on the counter. If the blank side is up eat them, it the M is up flip it again. Record how many you eat and how may you flip again. Keep doing that until you have eaten all of the M&M's then graph your data. Each time your flip the M&M's equals a half life and if you have a large enough sample size about half of the group will change each time.

That is the process that we use in geology. Every half life have of the existing population changes into the new element (eaten M&M's). By measuring the two element amounts you can find out the ratio and find out how many half lives. Scientist have figured out the length of the half lives for the elements and we use that to figure out how old the rock is.

Carbon dating uses material from living things, Potassium uses volcanic material, and I use Uranium to find the age of Zircons. They are a crystal which often makes up sand grains.

Answer 3

The correct term for what you ask is "radiometric" dating. The method used for each of your isotopes is pretty much the same. When radioactive elements decay they change from one element to another because of mass loss...usually either a proton or neutron. The resulting product is called the "daughter" product.

If I had 100 grams of a particular uranium isotope that took five years for half of it to decay to a new element (say lead or Pb) then we would say that that uranium isotope had a "half-life" of five years. So now, five years later we only have 50 grams left of uranium. Five years after that we would only have 25 grams....and five years later 12.5 grams, and five years later 6.25 grams. So if we knew we had an object that was supposed to have 100 grams of uranium in it but there was only 6.25 grams there, we could conclude the age of the object was 20 years old.

Taking carbon 14. Most all carbon is carbon 12, but there is a set small amount of C 14 in our environment. As long as a critter is alive, it takes in carbon (it is one of the building blocks of life). As long as the critter is alive, the ratio of C12 to C 14 is constant in its body. When the critter dies, it is no longer taking in carbon. Since the C 12 is stable and doesn't decay while the C 14 decays, the ratio of these two isotopes starts to change. Since we know what the original amount of C 14 should have been, and how much there is in the critter's remains now, we can figure out how long ago the critter died.

Several caveats are to be watched out for. First, there must be enough of the isotopes present to measure. Second, we must choose the correct isotopes to use. We can't use C 14 to date meteorites because its half life is too short and there wouldn't be enough to work with in a billion year old rock. So we use an isotope with a longer half-live...like potassium. We must also be careful there is no contamination of the specimen. Constant corrections must be made for C 14 work because of changes of the amount of carbon in our atmosphere due to things like industrial revolution, etc. We must have some approximate idea of the age of the item being tested so we can make these corrections. Is the critter from before the industrial revolution or after, for example.

Analyses to determine the amounts of some isotopes can be done using geiger counters, and plotting decay curves, or using mass spectrographs to determine the ratio of parent to daughter ratios, for example.

Answer 4

ok:
for Carbon-14... you know how all living things have carbon? Carbon is added while plants and animals grow, but when they die the carbon isn't added anymore and and existing carbon starts to decay. so ppl go and somehow measure out the remaining carbon in fossils and stuff and then they use this to figure out the absolute age of the rock.
for potassium argon... in really old rocks, the potassium decays to a stable element--argon. So ppl measure out the amount of argon in it and use it to find out the absolute age.
dunno about uranium, sorry.
i hope that's clear enough. I hope that helps, actually, because it's just what the science book says, and I kinda rephrased it a little. :) u learning it in science? i did it a few months ago... you can go read pg. 177 carefully if u haven't already done so.