Earth is the standard by which all Fantasy worlds are measured. 'Earth normal' gravity, 'Earth type' atmosphere, and more. While home to the human species since its creation, it is a world at once intimately familiar to humans – and so very alien to them. This one world has extremes that have spawned concepts for whole other worlds – and by the same token, is assumed to be habitable the world over when it is not.

http://en.wikipedia.org/wiki/Earth

For more information regarding the SisterWorlds in comparison, redirect to Earth

Geohammers for a list of geomallic events.