# Half life and radioactive dating cramster

Half-lives for various radioisotopes can range from a few microseconds to billions of years.

See the table below for a list of radioisotopes and each of unique their half-lives. After 86 minutes, half of the atoms in the sample would have decayed into another element, Lanthanum-139.

SAL: In the last video we saw all sorts of different types of isotopes of atoms experiencing radioactive decay and turning into other atoms or releasing different types of particles.

The half-lives of certain types of radioisotopes are very useful to know.

They allow us to determine the ages of very old artifacts.

Let's say I have a bunch of, let's say these are all atoms. And let's say we're talking about the type of decay where an atom turns into another atom. Or maybe positron emission turning protons into neutrons. And we've talked about moles and, you know, one gram of carbon-12-- I'm sorry, 12 grams-- 12 grams of carbon-12 has one mole of carbon-12 in it.

So you might get a question like, I start with, oh I don't know, let's say I start with 80 grams of something with, let's just call it x, and it has a half-life of two years.

Comparing that to the half-life of the nuclei tells when they started to decay and, therefore, how old the object is.

Perhaps the most widely used evidence for the Theory of Evolution through Natural Selection is the fossil record.The rate at which a radioactive isotope decays is measured in half-life.The term half-life is defined as the time it takes for one-half of the atoms of a radioactive material to disintegrate. So what we do is we come up with terms that help us get our head around this. So I wrote a decay reaction right here, where you have carbon-14. So now you have, after one half-life-- So let's ignore this. I don't know which half, but half of them will turn into it. And then let's say we go into a time machine and we look back at our sample, and let's say we only have 10 grams of our sample left. Now you could say, OK, what's the probability of any given molecule reacting in one second? But we're used to dealing with things on the macro level, on dealing with, you know, huge amounts of atoms. So I have a description, and we're going to hopefully get an intuition of what half-life means. And how does this half know that it must stay as carbon? So if you go back after a half-life, half of the atoms will now be nitrogen. Then all of a sudden you can use the law of large numbers and say, OK, on average, if each of those atoms must have had a 50% chance, and if I have gazillions of them, half of them will have turned into nitrogen. How much time, you know, x is decaying the whole time, how much time has passed? The fossil record may be incomplete and may never fully completed, but there are still many clues to evolution and how it happens within the fossil record.

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