Question

The following table shows the currently accepted half-life values for six parent isotopes.

Uranium-238 4.5 billion years
Uranium-235 704 million years
Thorium-232 14.0 billion years
Rubidium-87 48.8 billion years
Potassium-40 1.25 billion years
Samarium-147 106 billion years

Earth is approximately 4.5 billion years old. Given this information and the data in the table, which of the following isotopes could today contain less than 50 percent of its parent isotope?

Answer 1

The multiple choices are
A. Potassium-40
B. Rubidium-87
C. Samarium-147
D. Uranium-238

Answer 2

Try make a guess and explain why this time. Use the same argument I used in the last one.

Answer 3

Can help make some rules that are easy to remember:
Half life = Time (Earth's life team) -> Percentage = 50%
Half life < Time (Earth's life team) -> Percentage < 50%
Half life > Time (Earth's life team) -> Percentage > 50%

Answer 4

It would be Potassium-40 due to its half-life value being less than the Earth's age.

Answer 5

Am I correct?

Answer 6

Are you still there?
I am confused no what to do or how to start this.

Answer 7

*on
I apologize for my misspelling.

Answer 8

Never mind, it seems Potassium-40 was indeed the answer.
Thank you again for all your help!

Answer 9

Sorry I fell asleep.
But it looks like you can do it :) You are not totally lost.