Question

Scientists estimate Earth's age to be 4.6 billion years. Samarium has a half-life of approximately 106 billion years. From the present date, approximately how many more years must pass before a sample of samarium that was created at the beginning of Earth's history contains 25 percent of the original parent material?

10 billion

26 billion

100 billion

206 billion

Answer 1

\[\ln( N/N _{0})=-(\ln 2 \times t)/t _{1/2}\]
\[N/N _{0}=0.25\]
solving you get
\[t=2 \times t _{1/2}\]
Now subtract Earth's age
\[t-4.6 \times 10^{9}\]
you get the result you need.

Answer 2

??????

Answer 3

what?