Question

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

Parent Isotope Currently Accepted Half-Life Values
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?
Potassium-40
Rubidium-87
Samarium-147
Uranium-238

Answer 1

Potassium-40

Step-by-step explanation:

Got it right on the quiz.

Answer 2

The answer to your question is Potassium-40

Step-by-step explanation:

We know that the earth is approximately 4.5 billion years old, so to answer this question we must look for an isotope whose half-life is lower than 4.5 billion years.

Potassium-40 has a half-life of 1.25 billion years, this the isotope we are looking for.

Rubidium-87 has a half-life many times higher than 4.5 billion years, so this is not the answer.

Samarium-147 also has a half-life many times higher than 4.5 billion years, so this is not the correct answer.

Uranium-238 has a half-life equal to the age of the earth, so this is not the correct answer.