Radiometric dating definition geology
Radiometric dating definition geology - brian hwanhee dating
We define the rate of this radioactive decay in half-lives.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.
For geological purposes, this is taken as one year.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.Carbon-14, the radioactive isotope of carbon used in carbon dating has a half-life of 5730 years, so it decays too fast.It can only be used to date fossils younger than about 75,000 years.The same rock formation also contains a type of trilobite that was known to live 415 to 425 million years ago.
Since the rock formation contains both types of fossils the ago of the rock formation must be in the overlapping date range of 415 to 420 million years.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. There are two main methods determining a fossils age, relative dating and absolute dating.Relative dating is used to determine a fossils approximate age by comparing it to similar rocks and fossils of known ages.Scientists can use certain types of fossils referred to as index fossils to assist in relative dating via correlation.