What are tectonic plates?

When you picture the world, what do you see? Probably something like a map, or maybe a globe. A static picture of the planet we live and breathe on. You might imagine the continents, oceans, mountains, rivers, and more. But then you dig a little deeper.

Where did those mountains come from? Was there always an ocean there? Why do South America and Africa almost look like they fit together? The answer to those questions is that the Earth is not as static as it may look. In fact, the ground beneath our feet is constantly moving in slow motion. The world we see today is the product of billions of years of shifting and moving, inch by inch, year by year. This movement is known as Plate Tectonics.

How many tectonic plates are there?

Plates divide the entire surface of the Earth, also known as the Crust. There are around 16 widely recognized plates, 7 major plates and 9 minor plates. Think of the plates as pieces and the world as the puzzle.

What are tectonics plates?

What are Earth’s plates and how do they move? There are two main kinds of crust found on Earth, Oceanic crust and Continental crust. Oceanic crust is thin, dense, and is found at the bottom of every ocean. Its continental cousin is less dense but thicker, making up every continent. These crusts are divided into plates that all float on the second layer of the Earth, called the Aesthenosphere. The Aesthenosphere is the top part of the Mantle, a massive layer of churning rock under the crust.

When the Mantle moves and shifts, it moves the crust above it. This makes each plate independent, moving in its own direction. The places where plates meet is where the real magic happens. These are called plate boundaries. Plate boundaries are where plates literally rub shoulders with each other.

Let's talk plate boundaries

There are 3 main types of plate boundaries, each with their own sub-types. Together they are responsible for shaping the world as we know it. They are also a major part of the theory of Plate Tectonics. Let's take a closer look at these boundary types:

Spreading ridge: Spreading ridges form where the crust travels in opposite directions. As the plates separate, it causes molten rock from the mantle to rise through the crust and eventually reach the surface. As the rock cools, a new crust is created. The most famous of these is the Mid Atlantic Spreading Ridge. The ridge cuts across the entire Atlantic Ocean, slowly pushing the Americas away from Africa and Europe. This same ridge also cuts through Iceland, slowly pulling the island apart.

Collisions: On the more catastrophic side, plates can collide with each other. These are the plate boundaries that most people picture. Where plates collide, you often find extreme and striking landscapes. The Himalayas, the largest mountain range in the world, are a great example. They were formed from two continental plates that smashed into each other. The other collisions are known for creating another type of mountain: Volcanoes. The boundaries where you find volcanoes are Subduction zones. Subduction zones only form when oceanic crust travels beneath another type of crust. As it travels below the top plate and enters the mantle, it starts to melt. This melted crust rises up to the surface and over time a volcano forms. Places like Japan, Western South America, and Greece all sit on these collision zones.

Transform boundary: Finally, some plates just slide past each other. These are transform, or strike slip, boundaries. As the two plates slide past each other, they get stuck and build tension. Once that tension becomes too much, they snap past each other. This release of energy is called an earthquake. The San Andreas Fault system in California is a great example.

How fast do tectonic plates move?

Even after learning this, it can still be hard to really understand the scale of Earth’s plates. We might not be able to see the movement and changes in real time, but they are still happening. The world isn't fast but it is always changing. It was changing as you read this article, and will keep moving after you’ve finished it. One year from the time you read this sentence, North and South America will have moved an inch to the west. The Himalayas will grow by a centimeter as India continues to collide with Asia. Africa and Europe will inch closer and closer together. But the plates aren't the only things changing. Our understanding of the world moves with them.The theory of plate tectonics didn't just happen all at once, it took centuries of research. Great minds collided, thoughts formed, and over time the theory took shape into what it is now.

Thumbnail menu image of tectonic plates by Amitchell125 via Wikimedia Commons.