Absolute dating principles
The narrower a range of time that an animal lived, the better it is as an index of a specific time.No bones about it, fossils are important age markers.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.In a way this field, called geochronology, is some of the purest detective work earth scientists do.There are two basic approaches: relative age dating, and absolute age dating.
Absolute age dating is like saying you are 15 years old and your grandfather is 77 years old.
I also like this simple exercise, a spin-off from an activity described on the USGS site above.
Take students on a neighborhood walk and see what you can observe about age dates around you.
On the other hand, the half-life of the isotope potassium 40 as it decays to argon is 1.26 billion years.
So carbon 14 is used to date materials that aren’t that old geologically, say in the tens of thousands of years, while potassium-argon dating can be used to determine the ages of much older materials, in the millions and billions year range.