Question

Carbon-14 has a half-life of 5,730 years. If the age of an object older than 50,000 years cannot be determined by radiocarbon dating, then

* carbon-14 levels in a sample are undetectable after approximately ten half-lives.
* carbon-14 levels in a sample are undetectable after approximately nine half-lives.
* the half-life of carbon-14 is too long to accurately date the object.
* a radioisotope with a shorter half-life should be used to date the object.

Answer 1

A half life is the amount of time it takes for the total amount to decay by half.

So if you have 16 grams of something, after one half life you have 8 grams left. Another half life and you have 4 grams left, yet another and you will have 2, again 1, again 1/2, again 1/4, etc...

You really don't need to know how this works, since this is simply a division problem. How many half lives can you go through in 50,000 years? Well, divide the amount of time it takes for one half life to find out the total number of half lives.

You could set it up as:

\[50,000 years * \frac{ 1 half life }{ 5,370 years }=half lives\]

Answer 2

THANK you!!!! does that mean that the answer is D (from what i understand)?

Answer 3

Thanks!! :D

Answer 4

Well considering that 50,000/5730 is about 8.7 I would say B is the correct answer. Let's think about it, why would it not be D?

Well D would mean that you would be using a shorter half life, and then you would actually have more of the radioactive sample decay before you test it. If anything, you want longer half lives, because that means it takes longer for half of it to decompose!