The Earth's rocky outer crust solidified billions of years ago.
The theory of plate tectonics is a part of geology, or the study of the earth and how it changes. Developed in the 1960s and 1970s, this theory states that the earth's outer crust is made up of plates of rock that shift all over the globe. Tectonics is the branch of geology that studies these rock formations and how they change and affect the planet.
Who Discovered Plates?
In 1915, a German geologist named Alfred Wegener first proposed the theory that the earth's crust was not one solid piece of rock. Instead, he thought there were many large pieces that could drift around and bump into each other. His original theory was called "continental drift." He believed that all the continents on the planet look like they could have fit together like a puzzle, and that they used to be one big land mass that got broken up into smaller pieces and drifted apart. He really didn't have any explanation for why the continents split apart, so many other scientists didn't believe him. Even though he couldn't prove his theory, it gave scientists the foundation for the plate tectonics theory.
What Exactly Are Plates?
Plates are large pieces of rock in the earth's outer shell. The earth is made of the inner core, the outer core, the mantle and the crust. The crust has large plates that also fit together like loose pieces of a jig saw puzzle around the planet. Think of a hard-boiled egg. Ever seen one with lots of cracks in it? Think of this as the earth, and the cracks are where all the plates meet. The area where two plates meet is called a plate boundary. The shell pieces can shift around a little on top of the egg underneath. Think of the egg underneath the shell as the mantle of the earth. These plates can slip around on top of the earth's mantle just like the cracked egg shell does on the egg.
How Many Plates Are There?
The earth's outer layer is broken into seven large pieces, or plates. They are called the African, North American, South American, Eurasian, Australian, Antarctic and Pacific plates. All of these plates move in different directions, and at different speeds. They usually move between 2 cm to 10 cm per year. That's about the same speed that your fingernails grow.
What Happens if the Plates Shift too Much?
On the egg, if the shell slips too much, the edges might overlap. Sometimes you can even see pieces of the egg underneath pushing through. The same thing happens with the earth. If the plates shift against each other too much, the force can cause vibrations that shake and rumble. This is what causes earthquakes. Sometimes the shifting of the plates can even cause the rock formation to push straight up into the sky, causing mountains.
Tags: earth outer, large pieces, broken into, each other, outer crust
