Question

We will be exploring decay reactions used in radioactive dating of objects. This will be a short
lab to leave you time to prepare for the Unit 3 project.
1. Explore the PhET simulation Radioactive Dating Game . Try all the tabs to figure out why
there is more than one element used to estimate how old things might be.

2. What elements’ isotopes are used to estimate how old something is? Why do are more
than one type used?

3. Pretend you have a tool like the one on Dating Game tab:
a. How do you decide when to use Carbon-14 or Uranium-238?

b. How does the percentage help you estimate the age?

Answer 1

1.) More than one elements are used because different elements have different half-life. For example, half-life of C-14 is 5500 years while the half-life of Uranium is 4.5 billion years.

2.) Many elements are used for radioactive dating some of them are- Carbon-14, Thorium, Uranium, Polonium, Actinium etc. We use different elements depending on the nature of substance we are trying to date. For rocks we use Uranium-238 as its half life is quite large and for trees we can use Carbon-14.

3.

a)  When the estimated age is more(more than 1 million years e.g. rocks, asteroids) we use U-238 and when it is less(upto 100K years e.g. trees ,ruin of a monument) we use C-14

b.) We can use the percentage to estimate the age if we know the half life of the radioactive substance we are using by the formula

where P- percentage, t- estimated age and T - half-life of the element we have used.