Why is the Earth round?

The earth is round due to the operation of gravity radiating out from its substance equally in all directions. All matter exerts gravitational force; the bigger the mass, the greater the force that is exerted.

When the earth was forming, the force of gravity exerted from the aggregated matter that was to become the earth, pulled more and more matter towards itself forming the shape of a spheroid. Since gravity exerts itself equally from its source, the resulting shape is spherical, since the distance from the surface to the centre of a sphere is equal throughout. The earth is really an oblate spheroid rather than a perfect sphere largely due to its rotation.