Dating Rocks: Radiometric Methods
Dating Rocks: Radiometric Methods
Lesson duration is: 45 minItems in this lesson
Dating Rocks: Radiometric Methods
What do you already know about dating rocks using radioactive elements?
Learning Objective
At the end of the lesson you will understand how radiometric dating is used to determine the absolute age of rocks and the principle of half-life in radioactive decay.
Why Date Rocks?
Understanding the age of rocks helps scientists to study Earth's history, evolution, and major events such as the formation of mountains and extinction of species.
Relative vs Absolute Dating
Relative dating places rocks and events in order, but does not give exact ages. Absolute dating gives a precise age in years using scientific methods.
What Is Radiometric Dating?
Radiometric dating is a method that uses the decay of radioactive elements to calculate the exact age of rocks.
Radioactive Decay
Atoms of some elements are unstable. They change or decay over time, releasing energy. This process is called radioactive decay.
Parent & Daughter Isotopes
The original radioactive atom is called the parent isotope. The stable product formed is called the daughter isotope.
What Is a Half-Life?
Half-life is the time it takes for half of the parent isotopes in a sample to change into daughter isotopes.
Half-Life in Action
After one half-life, half the parent remains. After two, a quarter remains. This pattern continues and helps us measure the passage of time.
How Is Rock Age Measured?
Scientists measure amounts of parent and daughter isotopes in rocks using special instruments to calculate the age.
Common Radiometric Methods
Used for very old rocks. Uranium changes to lead over millions of years.
Carbon-14 Dating
Useful for dating once-living things up to 50,000 years old.
Uranium-Lead Dating
Practical Example
A rock sample contains 25% parent and 75% daughter isotopes. If the half-life is 1 million years, how old is the rock?
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Key Points Recap
Radiometric dating uses radioactive decay and half-life to find a rock's absolute age. These methods help us unlock Earth's history.
Write down 3 things you learned in this lesson.
Write down 2 things you want to know more about.
Ask 1 question about something you haven't quite understood yet.
