Today,the uranium found on Earth contains 0.720% ²³⁵U (with a half-life of 0.700 billion years)and 99.28% ²³⁸U (with a half-life of 4.50 billion years).At a time 2.20 billion years ago,what percent of the uranium on Earth was ²³⁸U (assuming that no other uranium isotopes were present)?

Question

Quizplus · Accepted Answer

To find the percentage of U-238 2.20 billion years ago, we use the decay formula for each isotope and the given current percentages. U-235 decays faster than U-238 due to its shorter half-life. Given the current percentages and the half-lives, we can calculate the original percentages 2.20 billion years ago, which shows that U-238 would have been a higher percentage of the total uranium due to its slower decay rate, leading to the correct answer.

Today,the Uranium Found on Earth Contains 0