Earth is a planet in the The Secondary Realms. It is the planet where humans evolved. According to the Architect, "Humans grew at a rate even I did not foresee". Most of the Denizens and technology within the House is based around the early 1900's Earth. It is the home of Arthur Penhaligon and his family and Leaf.
In Lady Friday 'some 1000 humans were taken from Earth.