Copyright

Using Geological Layers & Radioactive Dating to Determine the Earth's Age

Using Geological Layers & Radioactive Dating to Determine the Earth's Age
Coming up next: Developments & Extinctions of Life on the Geological Time Scale

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
 Replay
Your next lesson will play in 10 seconds
  • 0:02 How Old is the Earth?
  • 0:46 Geologic Layers
  • 2:04 Radioactive Dating
  • 3:00 Bringing It All Together
  • 4:16 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Timeline
Autoplay
Autoplay
Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Kevin Newton

Kevin has edited encyclopedias, taught middle and high school history, and has a master's degree in Islamic law.

If you want to know how old a person is, you ask them. If you want to get an idea about a tree's age, you count its rings. But what if you want to know the age of the Earth? In this lesson, we'll get an idea of how scientists date our planet.

How Old Is the Earth?

One of the most basic questions in geology centers on how old the Earth is. For centuries, people were happy to simply accept the teachings of mythology or religion. These datings put the age of the Earth anywhere from around 7,000 to trillions of years old. However, in the past few hundred years many people have been more inclined to use the scientific method to date the Earth. That doesn't make the rest of those belief systems any less valid, if they are what you believe, but we are looking for facts in science, the 'how' of Earth's existence, not the 'why.' To that end, scientists have a number of ways to try to figure out just how old the world is. In this lesson, we will look at two of those methods in particular - radioactive dating and the use of geological layers.

Geological Layers

Imagine you were making a cake with layers of fruit filling in between. I know, with that kind of talk it may be hard to focus on science, but I'm going to ask you to focus anyway. So imagine you were building this cake - where would you start? Chances are unless you are a magician and can make things float in mid-air, you'd start at the bottom. By the time you finished the cake, the deeper you went into the cake from the top, the longer it has been since that part of the cake has been on the surface. In fact, if you were to assemble a layer of cake a day, the lowermost layers would be older. They'd probably be stale, which changes the taste and texture of the cake.

Okay, enough of the cake analogy; however, it holds pretty well. The deeper we go into the Earth, more and more towards the core, the older the rock gets. This is the basic principle of geological layers. In fact, as we go deeper, the qualities of the rock change to reflect this age. Sedimentary rock, rock formed by layers of sediment being squeezed together, becomes more and more compact. Metamorphic rock, rock changed by immense pressure and heat, becomes even more common. In fact, we can use the occurrence of certain rocks to help figure out just how old a layer of rock is.

Radioactive Dating

Still, those rocks are only useful if we have something to compare them to. Wouldn't it be nice to just ask a rock when it was created? Well, luckily we can. Through the process of radioactive dating, we can figure out just how old a particular rock is based off the relative intensity of some substances within it. Think about it like this. Imagine each rock has a lantern that loses half of its brightness every so many years. This brightness is radioactive isotopes, or substances, which we can detect with the right equipment. The amount of time it takes for the rock to lose half of its radioactivity from a given isotope is called its half-life. The half-lives for different isotopes is pretty well known, as is the amount of a given isotope that is present in a given rock. Therefore, we can tell within a range how many half-life cycles that a rock has been through and adjust its age accordingly.

To unlock this lesson you must be a Study.com Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account
Support