Question

if an element has a half-life of 30 million years and there is 12.5% of it remaining in a rock, how old is that rock

Answer 1

The half-life of a substance is the amount of time it takes for half of that substance to decay. However, after two half-lives, half of the half remaining will decay, leaving you with one quarter of the original substance.

So, after 1 million years you will have 50% of the original substance remaining.

And, after 2 million years you will have 25% of the original substance remaining.

After 3 million years you will have 12.5% of the original substance remaining.

And after 4 million years you will have 6.25% of the original substance remaining.

Step-by-step explanation:

Hope it helps:)