Earth (also referred to by humans as "The World") is a celestial body which is the third planet from a star in a planetary system and is, currently, the only known point of origin for Humans and Machines in the universe.
Once a thriving home to billions of lifeforms, Earth has become a barren wasteland which lacks vegetation. It has become inhospitable for human habitation after decades of ongoing warfare around the early 22nd century.
Earth formed by accretion, when excess matter from its parent stars' genesis began clumping together into planets and moons. Its basalt crust cooled soon after its formation and collision with the protoplanet Theia. Its gasses appeared via outgassing, where volcanoes produce volatile gasses such as oxygen and nitrogen.
Its extensive bodies of water were produced from comets and other water-rich bodies crashing down on its surface. Life first appeared by abiogenesis, when the chemicals necessary for life began to fuse together and under the right conditions it turned into the first self-replicating molecule.
Life has proliferated over billions of years, until the sky darkening operation in attempt to block the energy source of the Machines. Eventually almost all life became extinct, resulting in a mass extinction bigger than the one that occurred during the Permian.
Earth's skies are filled with dark, rainless clouds that eternally blot out the sun. These clouds were created by humanity, who attempted to block the Machine's primary energy source through the use of rapidly multiplying nanomachines sprayed into the upper atmosphere. With the lack of sunlight, almost all life died and the world withered away, leaving a dark, cold desert of steel, dirt and debris.
Though it seems some plants and animals survived, as plants like trees, grass and shrubs are shown growing on the surface in The Miller's Tale, despite the scorched sky. Perhaps the clouds thickness isn't uniform and in some regions, the shroud is thin enough to allow photosynthesis to take place. Alternately these plants could have evolved to conduct photosynthesis at very low light levels or photosynthesize with different wavelengths of light that humans can't see.
It is presumed that every major city on Earth was destroyed by conventional or nuclear bombardment, or otherwise rendered virtually uninhabitable over the course of the Machine War. The only place where humans can live for more than a few generations is Zion, located close to the core which provides warmth and power
Zion is secreted away from 01, the machine city, whose inhabitants are unaffected by the lack of warmth or sunlight, as they derive their needed energies in part from many skyscraper-like cylindrical towers holding billions of synthetically-grown humans used for bioelectrical generation. The minds of the humans within the power plant are all but convinced that they conduct a normal life sometime at the end of the 20th century of the past, in a neural-interactive virtual world known as the Matrix.
During the domination of the machines, the Earth was attacked by Aliens, but the machines developed a plan to stop the attack.
After the Machine War and creation of the Matrix:
- The Machine City/Zero One
- Power plants
- Fetus fields
- Derelict ruins of numerous megacities, as well as miles of underground maintenance and access tunnels (sewers).
After the Truce: