Final answer:
The prime meridian, at 0 degrees longitude, divides the world into the Eastern and Western Hemispheres, with Europe, Asia, and Australia in the east, and the Americas in the west.
Step-by-step explanation:
The important line that breaks the World up into the Eastern and Western Hemispheres is the prime meridian. The prime meridian is defined as an imaginary line that runs through the Royal Observatory in Greenwich, England.
This meridian is set at 0 degrees longitude and is the reference point for all other lines of longitude, which are measured in degrees east or west from this line.
The continents of Europe, Asia, and Australia are located in the Eastern Hemisphere, while North and South America are in the Western Hemisphere. When standing on the prime meridian, one can have a foot in each hemisphere.