Difference between relative absolute dating
These isotopes break down at a constant rate over time through radioactive decay.
By measuring the ratio of the amount of the original (parent) isotope to the amount of the (daughter) isotopes that it breaks down into an age can be determined.
So, often layers of volcanic rocks above and below the layers containing fossils can be dated to provide a date range for the fossil containing rocks.
The atoms in some chemical elements have different forms, called isotopes.
Potassium-40 on the other hand has a half like of 1.25 billion years and is common in rocks and minerals.
This makes it ideal for dating much older rocks and fossils.
If a radioactive isotope is said to have a half-life of 5,000 years that means after 5,000 years exactly half of it will have decayed from the parent isotope into the daughter isotopes.
Then after another 5,000 years half of the remaining parent isotope will have decayed.
While people are most familiar with carbon dating, carbon dating is rarely applicable to fossils.
The age of the fossil must be determined so it can be compared to other fossil species from the same time period.
Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms.Scientists can use certain types of fossils referred to as index fossils to assist in relative dating via correlation.