This uses radioactive minerals that occur in rocks and fossils almost like a geological clock.
It’s often much easier to date volcanic rocks than the fossils themselves or the sedimentary rocks they are found in.
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.
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.
Scientists can use certain types of fossils referred to as index fossils to assist in relative dating via correlation.
If the fossil you are trying to date occurs alongside one of these index fossils, then the fossil you are dating must fall into the age range of the index fossil. In a hypothetical example, a rock formation contains fossils of a type of brachiopod known to occur between 410 and 420 million years.The Wheeler Formation has been previously dated to approximately 507 million year old, so we know the trilobite is also about 507 million years old.But, how can we determine how old a rock formation is, if it hasn’t previously been dated?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.
Studying the layers of rock or strata can also be useful. If a layer of rock containing the fossil is higher up in the sequence that another layer, you know that layer must be younger in age. This can often be complicated by the fact that geological forces can cause faulting and tilting of rocks.