Actually, it’s not perfectly round. It’s an “oblate spheroid,’’ a sphere that’s slightly wider at the Equator than at the Poles. Gravity squashed Earth and the solar system’s other planets into spherical shapes back when they formed from clouds of dust and gas. Earth’s rotation is what causes its slight bulge around the middle.
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.
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.
Picture Credit : Google