Here is an easy-to understand analogy for your students: relative age dating is like saying that your grandfather is older than you. This technique is based on the principle that all objects absorb radiation from the environment. Heating an item to 500 degrees Celsius or higher releases the trappedproducing light.That’s because zircon is super tough – it resists weathering. Each radioactive isotope works best for particular applications.
Pretty obvious that the dike came after the rocks it cuts through, right.
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.
Pretty obvious that the dike came after the rocks it cuts through, right?
With absolute age dating, you get a real age in actual years.
Look for “absolute” ages such as cornerstones, dates carved into fresh concrete, or dates stamped on manhole covers.