Dating rocks and fossils and geologic events
It can only be used to date fossils younger than about 75,000 years.Potassium-40 on the other hand has a half like of 1.25 billion years and is common in rocks and minerals.
Then after another 5,000 years half of the remaining parent isotope will have decayed.
Index fossils are fossils that are known to only occur within a very specific age range.
Typically commonly occurring fossils that had a widespread geographic distribution such as brachiopods, trilobites, and ammonites work best as index fossils.
While people are most familiar with carbon dating, carbon dating is rarely applicable to fossils.
Carbon-14, the radioactive isotope of carbon used in carbon dating has a half-life of 5730 years, so it decays too fast.
It’s often much easier to date volcanic rocks than the fossils themselves or the sedimentary rocks they are found in.