Question

Uranium-238 has a half-life of 4.5 billion years. Given that scientists estimate Earth's age to be 4.6 billion years, what is the most likely percentage of parent to daughter isotopes of this element currently existing on Earth? 10 percent 25 percent 50 percent 75 percent

Answer 1

I haven't heard the parent-daughter isotope phrase used in this problem before, but after approximately one half-life has gone by.... approximately 50% of the radioactive element is left. This comes from the definition of half-life as: the amount of time that it takes for half of the original amount of radioactive material to decay.