The potassium 40 to calcium or argon 40 half-life is 1.25 billion years so if this half-life is displayed then the age of 1.25 billion years would be valid. Half life is the time it takes for an isotope to decay into half its' amount and which in the process is losing its radioactivity.
Can you specify what the geophysicists are looking for?
Answer:
Carbon
Explanation:
Carbon is the most essential element to make organic compounds found in all organisms.
That's why carbon dating technique is used to know the age of fossils of any organisms.