Question

Earth science help with all questions

1. We start with 400 atoms of uranium-238. How many remain after 4.5 billion years?
After 9 billion years
After 13.5 billion years

Answer 1

to answer this question, we just need to count the half-live

The half-live of uranium-238 is around 4.5 billion year, so

after 4.5 billion years = 400/2 = 200 atoms
after 9 billion years = 200/2 = 100 atoms
after 13.5 billion years = 100/2 = 50 atoms