Answer:
180 million years
Explanation:
Data provided in the question:
Rock sample has 2 pg/kg of a radioactive isotope
Isotope of the modern rock formed = 64 pg/kg
Half life of the isotope = 30 million years
Now,
From 128ug/kg to 2 ug/kg,
Number of half-lives elapsed = 6
Therefore,
The Age of the rock sample
= Half life of the isotope × Number of half-lives elapsed
= 30 million years × 6
= 180 million years
