Sea Floor Spreading: Definition, Theory & Facts

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Optical Properties of Minerals: Luster, Light Transmission, Color & Streak

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

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:03 What Is Sea Floor Spreading?
  • 0:42 Spreading: How and Where?
  • 2:01 How Did People Learn This?
  • 2:58 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

Speed Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Terry Dunn

Terry has a master's degree in environmental communications and has taught in a variety of settings.

The continents are on the move and sea floor spreading helps to explain how. Here you will learn what sea floor spreading is, how it works, where it is happening, and what led to its discovery.

What Is Sea Floor Spreading?

Have you ever watched a cake baking in the oven? You know that moment when the top starts to cook and split when you can see that that gooey batter in the crack? It eventually cooks, too. Well, it turns out that the surface of the earth is also a little like that. The crusty surface of the cake is similar to the earth's tectonic plates, which are gigantic, slowly-moving pieces of the earth's crust. The uncooked 'batter' between the plates would be the magma. When the magma cools, it becomes part of the earth's crust. Where the plates are moving away from each other, they are called divergent plates. The shifting divergent plates under the ocean are the reason for sea floor spreading.

Spreading: How and Where?

Just like the cracks on a baking cake, long ridges called mid-ocean ridges form at the point of sea floor spreading. Think of them as underwater mountain chains. One of the more well-known mid-ocean ridges is the Mid-Atlantic Ridge. It splits the North American and Eurasian plates apart in the North, and the South American and African plates in the South. But there is a global mid-ocean ridge system which looks like a series of global zippers that the Mid-Atlantic Ridge is part of.

Wherever the sea floor is spreading, the edges move apart while the magma in the middle hardens. That means the rock in the center is the youngest. As the continents move apart, whole new oceans can form. Scientists believe that's how the Red Sea came into existence. 

So you may be wondering: if the sea floor is spreading is some places, wouldn't the planet be getting bigger? It seems logical, but the answer is that other parts the planet are shrinking at the same time! There are also convergent plates, where one plate moves underneath another plate. At those points in the ocean, called oceanic trenches, the earth is literally losing ground. Oceanic trenches tend to be along the margins of the continents, and most are on the margins of the Pacific Ocean. It's these areas that are most prone to earthquakes.

To unlock this lesson you must be a 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

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
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? 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