What divide the earth from eastern and western hemisphere?

The Prime Meridian, an imaginary line running between the North and South poles of Earth, and the International Date Line, its counterpart on the opposite side of the world, both divide the Earth into its 2 halves, the Eastern and Western hemispheres.

Note: The Equator divides the Earth into its other 2 hemispheric dinstinctions: the North and South hemispheres.