Radiometric dating rock strata
Each original isotope, called the parent, gradually decays to form a new isotope, called the daughter.
Each isotope is identified with what is called a ‘mass number’.
Unlike people, you can’t really guess the age of a rock from looking at it.
Yet, you’ve heard the news: Earth is 4.6 billion years old. That corn cob found in an ancient Native American fire pit is 1,000 years old. Geologic age dating—assigning an age to materials—is an entire discipline of its own.
Relative age dating also means paying attention to crosscutting relationships.
Say for example that a volcanic dike, or a fault, cuts across several sedimentary layers, or maybe through another volcanic rock type.
The atoms of some chemical elements have different forms, called isotopes.
These break down over time in a process scientists call radioactive decay.
Isotopes are important to geologists because each radioactive element decays at a constant rate, which is unique to that element.This is different to relative dating, which only puts geological events in time Most absolute dates for rocks are obtained with radiometric methods.These use radioactive minerals in rocks as geological clocks.Using relative dating the fossil is compared to something for which an age is already known.For example if you have a fossil trilobite and it was found in the Wheeler Formation.