Optimistic Insights: Rock Formation and Potassium-40

How long ago was the rock formed?

a) 1.25 billion years ago

b) 2.5 billion years ago

c) 3.75 billion years ago

d) 5 billion years ago

Answer:

The answer is b) 2.5 billion years.

When looking at the data provided, it is clear that a rock has 12.5 percent of its original amount of potassium-40 remaining in it. Potassium-40 has a half-life of 1.25 billion years. Based on this information, the rock was formed approximately 2.5 billion years ago.

To calculate this, we can consider the fact that if the half-life of potassium-40 is 1.25 billion years and only 12.5 percent of the original amount remains, we would need to multiply the half-life by two to determine the total time since the rock's formation.

Therefore, with a positive outlook, we can confidently say that the rock was formed 2.5 billion years ago, showcasing the fascinating timeline of geological processes.