Why is the earth round?

When you see a picture of our earth from space, it looks exactly like a round blue and white marble. When seen from further out in space (at the end of our Milky Way galaxy), a famous astronomer, Dr. Carl Sagan, called it ‘A Pale Blue Dot’. But looks can be deceiving. Our earth is not really ‘round’, it is a shape called an ‘ellipsoid’ which is kind of squatty and fat. While you don’t notice it, the earth is also constantly changing its shape.


It is a fact that we have a ‘pudgy’ planet. The earth is fatter in the middle than at both of the polar ends. The center or ‘equator’ is the fattest part of all. You might not be able to tell that in any of the pictures, but it’s true. The reason for the chunkier look to the planet is because earth is constantly turning and something called ‘centrifugal force’ pushes everything to the center of the planet and out.

It is believed that the earth, like all of the planets in our solar system, formed 4.6 billion years ago, when asteroids began crashing into each other and then stuck together. When they slammed into each other they made everything spin. The more it was spinning, the more closely packed everything became, until it started looking like a round ball. The bigger it got, the stronger the ‘gravity’ and that made it push and hold together even more.

Shape of Earth

We might think the ground we are standing on is firm, but thousands of feet underneath are ‘tectonic plates’ that are constantly on the move. This movement is slow and steady and it takes millions of years to make any changes. When there is a sudden shift in these plates, it is an earthquake. Other movements on the surface of the earth are the massive ocean tides. The tides shift every day when the gravity of our moon ‘pulls’ them closer. Both of these kinds of movements have a drastic effect on the shape of the earth. They push and pull so that the earth bulges.

There are other things that happen on the earth that can make its shape change. Volcanic eruptions under the ocean as well as on land, can be quite violent. It causes the earth to shake and shift, bringing the hot magma from under the surface and creating new land. Deep beneath the earth there is a lot of pressure pushing to the top. This pressure can push up and create new mountains. All of these can cause the earth to alter its shape.

There are scientists in many countries that take notes and follow all of the changes in the earth.. They know this process has been going on for billions of years and it is part of the natural order. The information that they gather is kept in records, with the hope that it can help to figure out when a volcano might erupt or even if there will be an earthquake.

Just because we can’t see that the earth is not perfectly round, doesn’t mean we can’t still call it round. To all of us, it is still the blue and white marble in our solar system. The place that we call home.

National Ocean Service

BBC – The Earth Forms