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Why are all of the Earth's layers circular?
Question Date: 2015-02-23
Answer 1:

The Earth's layers are more like spheres (or balls) than circles. Imagine each layer like a thick coat of paint around a ball. They can look like circles if you draw a side-view (called a "cross-section") of the inside of the Earth.

The primary reason for this shape is gravity. Gravity pulls objects toward the center of the Earth from every direction around it. Because of this, a perfectly symmetric pile of rocks can form around the center of the Earth in the shape of a ball (a sphere).

Some of the Earth's layers are solid (like rocks), while other layers are softer, like toothpaste. The material inside the Earth can form into nice layers really easy if they can move around like toothpaste. Gravity will make the layers even because it pulls evenly from all directions. It's like spreading peanut butter on your bread: gravity wants to make a symmetric layer, therefore the layers will be evenly spread around the center of the Earth. The only shape that is evenly spread (perfectly symmetric) in every direction around the center of the Earth is a sphere. That is why all the layers in the Earth are spherical (or circluar in a side-veiw).

Answer 2:

Great question! It's one of those things we seem to take for granted. Well, circles (if we're talking 2D) and spheres (if we're talking 3D, or an object) happen to be the easiest shapes to form in nature. Forming a circle or a sphere takes the least energy, which nature tries to do for the most part. When Earth was first coming together and getting bigger, gravity pulled everything together and a sphere is what was created. I hope I gave you a satisfying answer. Good luck with your studies!

Answer 3:

Hi. This is a really good question and it comes back to the question why the Earth is (nearly) a ball, why is the Earth spherical? (A “sphere” is a fancy word for “ball”). Why is the sun spherical And all of the planets? The answer to these questions lies in the force called “gravity”. Gravity is the force that makes apples fall to the ground, that makes you stay on the Earth surface and not fly away and that makes the Earth rotate around the sun. Anything in the universe (you, me, the tree in the garden, your house etc.) attracts other material because of gravity. Yes, you understood correctly, you attract the tree in the garden and the tree in the garden attracts you. However, the force between you and the tree is so small that you cannot feel it. The strength of the force of gravity depends on the size of the object. You and the tree are relatively small objects. However, the Earth is a massive object and therefore it has a very large force and attracts you and attracts the apple on the tree, etc. This gravity force also caused the Earth to be formed in the first place as it attracted more and more material from the dust that the solar system, was formed from. As more and more dust came together and the Earth got larger and larger, the gravity force got stronger and attracted even more dust so the Earth got larger and so on. This is the first part of the puzzle and this force explains why the Earth is a sphere (or a ball).

Everything is attracted to the center of the Earth and moves as close as it can. The only way to arrange material as close as possible to the center of an objects is to form a sphere around the center. Try to tear out a small piece of paper and mark in in red. Put this in the middle of the table. Now add more and more small pieces of paper around this center piece and put them as close to the center piece as possible without touching another piece of paper. If any piece of paper can be closer to the center without touching another piece, you have to move it. As you add more and more pieces of paper, you will see that you have to arrange them in a circle around the center and just the same way, the “pieces” of the Earth are arranged in circles around the center (and in three dimensions, circles become a sphere). Does that make sense?

If you understood this, then the next step is simple. The layers of the Earth are there because there is heavier material in the core of the Earth (mostly Iron and Nickel) and lighter material on the outside of the Earth. The heavy iron and nickel sank to the core when the Earth was very hot. Because of gravity, all the Iron needs to be as close as possible to the center of the Earth and arranged in a spherical shape. Similarly, the other layers of the earth formed “circles” around the center.

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